diff --git a/.codecov.yml b/.codecov.yml
index cd52e2604d4..4268758e442 100644
--- a/.codecov.yml
+++ b/.codecov.yml
@@ -1,10 +1,32 @@
 codecov:
   require_ci_to_pass: true
+  # The C++ and Rust uploads land minutes apart; without this gate Codecov
+  # publishes a near-zero total from whichever one arrives first.
+  notify:
+    after_n_builds: 2
+    wait_for_ci: true
 
 comment:
   behavior: default
   layout: reach,diff,flags,tree,reach
-  show_carryforward_flags: false
+  show_carryforward_flags: true
+  after_n_builds: 2
+
+# C++ and Rust coverage upload from independent workflows under the `cpp` and
+# `rust` flags; carryforward keeps one language's total when only the other reran.
+flag_management:
+  default_rules:
+    carryforward: true
+  individual_flags:
+    - name: cpp
+      carryforward: true
+      paths:
+        - include/
+        - src/
+    - name: rust
+      carryforward: true
+      paths:
+        - crates/
 
 coverage:
   range: "70..85"
diff --git a/.cspell.config.yaml b/.cspell.config.yaml
index b014b08eb2d..95b457272c0 100644
--- a/.cspell.config.yaml
+++ b/.cspell.config.yaml
@@ -7,7 +7,6 @@ ignorePaths:
   - cmake/**
   - LICENSE.md
   - .clang-tidy
-  - src/test/app/wasm_fixtures/*.c
 language: en
 allowCompoundWords: true # TODO (#6334)
 ignoreRandomStrings: true
@@ -105,6 +104,7 @@ words:
   - deleteme
   - demultiplexer
   - deserializaton
+  - desugars
   - desync
   - desynced
   - determ
@@ -130,6 +130,7 @@ words:
   - gcov
   - gcovr
   - ghead
+  - gmock
   - Gnutella
   - godexsoft
   - gpgcheck
@@ -139,7 +140,9 @@ words:
   - hwaddress
   - hwrap
   - ifndef
+  - impls
   - inequation
+  - initialiser
   - insuf
   - insuff
   - invasively
@@ -247,6 +250,7 @@ words:
   - pyparsing
   - qalloc
   - qbsprofile
+  - qself
   - queuable
   - Raphson
   - rcflags
@@ -311,6 +315,7 @@ words:
   - summands
   - superpeer
   - superpeers
+  - Swatinem
   - takergets
   - takerpays
   - ters
@@ -339,6 +344,7 @@ words:
   - unflatten
   - unfund
   - unimpair
+  - unmetered
   - unroutable
   - unscalable
   - unserviced
@@ -359,6 +365,7 @@ words:
   - vfalco
   - vinnie
   - wasmi
+  - Werror
   - wextra
   - wptr
   - writeme
diff --git a/.github/dependabot.yml b/.github/dependabot.yml
index fcac44c44c5..1ece5793286 100644
--- a/.github/dependabot.yml
+++ b/.github/dependabot.yml
@@ -19,3 +19,20 @@ updates:
       github-actions:
         patterns:
           - "*"
+
+  - package-ecosystem: cargo
+    directory: /crates
+    schedule:
+      interval: weekly
+      day: monday
+      time: "04:00"
+      timezone: Etc/GMT
+    commit-message:
+      prefix: "ci: [DEPENDABOT] "
+    target-branch: develop
+    open-pull-requests-limit: 10
+    # Bundle all Rust dependency bumps into a single PR per run to reduce noise.
+    groups:
+      rust-dependencies:
+        patterns:
+          - "*"
diff --git a/.github/workflows/cargo-audit.yml b/.github/workflows/cargo-audit.yml
new file mode 100644
index 00000000000..2205018214b
--- /dev/null
+++ b/.github/workflows/cargo-audit.yml
@@ -0,0 +1,84 @@
+# This workflow audits the Rust dependencies in crates/ for known security
+# advisories using cargo-audit. It runs on a weekly schedule, whenever the
+# dependency graph changes (Cargo.lock / Cargo.toml), and on demand. On a
+# scheduled run, a failure opens a tracking issue (matching the clang-tidy
+# workflow's behavior); on push/PR it simply fails the check.
+name: Cargo audit
+
+on:
+  schedule:
+    # 06:32 UTC every Monday.
+    - cron: "32 6 * * 1"
+  push:
+    branches:
+      - "develop"
+      - "release*"
+    paths:
+      - "crates/**/Cargo.toml"
+      - "crates/Cargo.lock"
+      - ".github/workflows/cargo-audit.yml"
+  pull_request:
+    paths:
+      - "crates/**/Cargo.toml"
+      - "crates/Cargo.lock"
+      - ".github/workflows/cargo-audit.yml"
+  workflow_dispatch:
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+defaults:
+  run:
+    shell: bash
+    working-directory: crates
+
+permissions:
+  contents: read
+
+jobs:
+  audit:
+    runs-on: ubuntu-latest
+    container: ghcr.io/xrplf/xrpld/nix-debian:sha-2e25435
+    permissions:
+      contents: read
+      # Needed to open an issue on scheduled failures.
+      issues: write
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
+
+      - name: Run cargo audit
+        id: audit
+        continue-on-error: true
+        run: |
+          set -o pipefail
+          cargo audit | tee /tmp/cargo-audit.txt
+
+      - name: Prepare issue body
+        if: ${{ steps.audit.outcome != 'success' && github.event_name == 'schedule' }}
+        run: |
+          {
+              echo "## \`cargo audit\` found advisories"
+              echo
+              echo '```'
+              cat /tmp/cargo-audit.txt
+              echo '```'
+              echo
+              echo "---"
+              echo "*This issue was automatically created by the cargo-audit workflow.*"
+          } >/tmp/cargo-audit-issue.md
+
+      - name: Create issue
+        if: ${{ steps.audit.outcome != 'success' && github.event_name == 'schedule' }}
+        uses: XRPLF/actions/create-issue@2b8bc36af85b88bca0dd7bfac2e2dc05f94ad712
+        with:
+          title: "cargo audit found vulnerabilities"
+          body_file: /tmp/cargo-audit-issue.md
+          labels: "Bug,Security"
+
+      - name: Fail if advisories were found
+        if: ${{ steps.audit.outcome != 'success' }}
+        run: |
+          echo "cargo audit found advisories!"
+          exit 1
diff --git a/.github/workflows/on-pr.yml b/.github/workflows/on-pr.yml
index 0a4e4b1f49c..b3ac3a28065 100644
--- a/.github/workflows/on-pr.yml
+++ b/.github/workflows/on-pr.yml
@@ -85,6 +85,7 @@ jobs:
             .github/workflows/reusable-check-autogen.yml
             .github/workflows/reusable-clang-tidy.yml
             .github/workflows/reusable-package.yml
+            .github/workflows/reusable-rust.yml
             .github/workflows/reusable-strategy-matrix.yml
             .github/workflows/reusable-test.yml
             .github/workflows/reusable-upload-recipe.yml
@@ -95,6 +96,7 @@ jobs:
             cfg/**
             cmake/**
             conan/**
+            crates/**
             external/**
             include/**
             src/**
@@ -168,6 +170,13 @@ jobs:
     secrets:
       CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
 
+  rust:
+    needs: should-run
+    if: ${{ needs.should-run.outputs.go == 'true' }}
+    uses: ./.github/workflows/reusable-rust.yml
+    secrets:
+      CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
+
   package:
     needs: [should-run, build-test]
     # Packaging consumes the debian/rhel release binaries, which are only built
@@ -211,6 +220,7 @@ jobs:
       - check-rename
       - clang-tidy
       - build-test
+      - rust
       - package
       - upload-recipe
       - notify-clio
diff --git a/.github/workflows/on-trigger.yml b/.github/workflows/on-trigger.yml
index 73f918d5287..7a1a359cdcf 100644
--- a/.github/workflows/on-trigger.yml
+++ b/.github/workflows/on-trigger.yml
@@ -23,6 +23,7 @@ on:
       - ".github/workflows/reusable-check-autogen.yml"
       - ".github/workflows/reusable-clang-tidy.yml"
       - ".github/workflows/reusable-package.yml"
+      - ".github/workflows/reusable-rust.yml"
       - ".github/workflows/reusable-strategy-matrix.yml"
       - ".github/workflows/reusable-test.yml"
       - ".github/workflows/reusable-upload-recipe.yml"
@@ -33,6 +34,7 @@ on:
       - "cfg/**"
       - "cmake/**"
       - "conan/**"
+      - "crates/**"
       - "external/**"
       - "include/**"
       - "src/**"
@@ -96,6 +98,11 @@ jobs:
     secrets:
       CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
 
+  rust:
+    uses: ./.github/workflows/reusable-rust.yml
+    secrets:
+      CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
+
   upload-recipe:
     needs: build-test
     # Only run when pushing to the develop branch.
diff --git a/.github/workflows/reusable-build-test-config.yml b/.github/workflows/reusable-build-test-config.yml
index d8550efc4ce..ecdbbbbe86c 100644
--- a/.github/workflows/reusable-build-test-config.yml
+++ b/.github/workflows/reusable-build-test-config.yml
@@ -276,7 +276,7 @@ jobs:
         working-directory: ${{ env.BUILD_DIR }}
         run: |
           ldd ./xrpld
-          if [ "$(ldd ./xrpld | grep -E '(libstdc\+\+|libgcc)' | wc -l)" -eq 0 ]; then
+          if [ "$(ldd ./xrpld | grep -E '(libstdc\+\+)' | wc -l)" -eq 0 ]; then
               echo 'The binary is statically linked.'
           else
               echo 'The binary is dynamically linked.'
@@ -289,6 +289,14 @@ jobs:
         run: |
           ./xrpld --version | grep libvoidstar
 
+      - name: Run Rust tests
+        if: ${{ !inputs.build_only }}
+        working-directory: crates
+        # `xrpl-wasm-vm-ffi` is left out on Windows: its tests link as an executable, and
+        # MSVC - unlike the Unix linkers - will not dead-strip the never-called cxx wrappers
+        # whose C++ shims only the CMake build defines. The other runners cover these tests.
+        run: cargo nextest run --workspace --all-features --locked --no-tests=warn ${{ runner.os == 'Windows' && '--exclude xrpl-wasm-vm-ffi' || '' }}
+
       - name: Run the separate tests
         if: ${{ !inputs.build_only }}
         working-directory: ${{ runner.os == 'Windows' && format('{0}/{1}', env.BUILD_DIR, inputs.build_type) || env.BUILD_DIR }}
@@ -394,6 +402,7 @@ jobs:
           disable_telem: true
           fail_ci_if_error: true
           files: ${{ env.BUILD_DIR }}/coverage.xml
+          flags: cpp
           plugins: noop
           token: ${{ secrets.CODECOV_TOKEN }}
           verbose: true
diff --git a/.github/workflows/reusable-clang-tidy.yml b/.github/workflows/reusable-clang-tidy.yml
index f1fdc0569ad..983972e8c15 100644
--- a/.github/workflows/reusable-clang-tidy.yml
+++ b/.github/workflows/reusable-clang-tidy.yml
@@ -88,6 +88,12 @@ jobs:
         run: |
           ninja -j ${{ steps.nproc.outputs.nproc }} xrpl.libpb
 
+      # clang-tidy needs cxxbridge headers generated from Rust crates
+      - name: Build xrpl_crates
+        working-directory: ${{ env.BUILD_DIR }}
+        run: |
+          ninja -j ${{ steps.nproc.outputs.nproc }} xrpl_crates
+
       - name: Run clang tidy
         id: run_clang_tidy
         continue-on-error: true
diff --git a/.github/workflows/reusable-rust.yml b/.github/workflows/reusable-rust.yml
new file mode 100644
index 00000000000..33726b2425a
--- /dev/null
+++ b/.github/workflows/reusable-rust.yml
@@ -0,0 +1,86 @@
+# Clippy, coverage and documentation for the Rust crates in crates/. Each runs
+# as an independent job on a GitHub-hosted runner, but inside the same container
+# image used to build the crates in the C++/Corrosion path, so the toolchain
+# (and therefore the lints, coverage instrumentation and the cargo cache) matches
+# what production builds use.
+#
+# Rust unit tests are deliberately NOT run here. They run as part of the C++
+# build (reusable-build-test-config.yml), which already compiles the crates on a
+# self-hosted runner, so there is no need to provision a toolchain again.
+name: Rust
+
+on:
+  workflow_call:
+    secrets:
+      CODECOV_TOKEN:
+        description: "The Codecov token to use for uploading coverage reports."
+        required: false
+
+defaults:
+  run:
+    shell: bash
+    working-directory: crates
+
+permissions:
+  contents: read
+
+jobs:
+  clippy:
+    runs-on: ubuntu-latest
+    container: ghcr.io/xrplf/xrpld/nix-ubuntu:sha-fecfc0c
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
+
+      - name: Cache cargo artifacts
+        uses: Swatinem/rust-cache@c19371144df3bb44fab255c43d04cbc2ab54d1c4 # v2.9.1
+        with:
+          workspaces: crates
+
+      - name: Run clippy
+        run: cargo clippy --workspace --all-targets --all-features --locked -- -D warnings
+
+  coverage:
+    runs-on: ubuntu-latest
+    container: ghcr.io/xrplf/xrpld/nix-ubuntu:sha-fecfc0c
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
+
+      - name: Cache cargo artifacts
+        uses: Swatinem/rust-cache@c19371144df3bb44fab255c43d04cbc2ab54d1c4 # v2.9.1
+        with:
+          workspaces: crates
+
+      - name: Generate coverage report
+        run: cargo llvm-cov nextest --workspace --all-features --locked --no-tests=warn --lcov --output-path lcov.info
+
+      - name: Upload coverage report
+        if: ${{ github.repository == 'XRPLF/rippled' }}
+        uses: codecov/codecov-action@fb8b3582c8e4def4969c97caa2f19720cb33a72f # v7.0.0
+        with:
+          disable_search: true
+          disable_telem: true
+          fail_ci_if_error: true
+          files: crates/lcov.info
+          flags: rust
+          plugins: noop
+          token: ${{ secrets.CODECOV_TOKEN }}
+          verbose: true
+
+  doc:
+    runs-on: ubuntu-latest
+    container: ghcr.io/xrplf/xrpld/nix-ubuntu:sha-fecfc0c
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
+
+      - name: Cache cargo artifacts
+        uses: Swatinem/rust-cache@c19371144df3bb44fab255c43d04cbc2ab54d1c4 # v2.9.1
+        with:
+          workspaces: crates
+
+      - name: Build documentation
+        env:
+          RUSTDOCFLAGS: "-D warnings"
+        run: cargo doc --workspace --no-deps --all-features --locked
diff --git a/.gitignore b/.gitignore
index 13b59a7e2ce..c5af8eb7b4a 100644
--- a/.gitignore
+++ b/.gitignore
@@ -89,3 +89,6 @@ target/
 
 # clangd cache
 /.cache
+
+# Rust build directory
+crates/target
diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index d339cb29ed5..e5e69759fd9 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -62,6 +62,15 @@ repos:
         types_or: [c++, c, proto]
         exclude: ^include/xrpl/protocol_autogen/(transactions|ledger_entries)/
 
+  - repo: local
+    hooks:
+      - id: cargo-fmt
+        name: cargo fmt
+        entry: cargo fmt --manifest-path crates/Cargo.toml --all
+        language: system
+        types: [rust]
+        pass_filenames: false # rustfmt formats the whole workspace
+
   - repo: https://github.com/BlankSpruce/gersemi-pre-commit
     rev: e98930bdc210d3387007f9252d8c1694ea7e410f # frozen: 0.27.7
     hooks:
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 4765a5a7081..e7cb13e96af 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -114,7 +114,6 @@ find_package(OpenSSL REQUIRED)
 find_package(secp256k1 REQUIRED)
 find_package(SOCI REQUIRED)
 find_package(SQLite3 REQUIRED)
-find_package(wasmi REQUIRED)
 find_package(xxHash REQUIRED)
 
 target_link_libraries(
@@ -159,6 +158,7 @@ if(coverage)
     include(XrplCov)
 endif()
 
+add_subdirectory(crates)
 include(XrplCore)
 include(XrplProtocolAutogen)
 include(XrplInstall)
diff --git a/cmake/XrplCore.cmake b/cmake/XrplCore.cmake
index 7c1eb5688a1..feea6f2a542 100644
--- a/cmake/XrplCore.cmake
+++ b/cmake/XrplCore.cmake
@@ -67,7 +67,6 @@ target_link_libraries(
         Xrpl::opts
         Xrpl::syslibs
         secp256k1::secp256k1
-        wasmi::wasmi
         xrpl.libpb
         xxHash::xxhash
         $<$<BOOL:${voidstar}>:antithesis-sdk-cpp>
@@ -206,7 +205,17 @@ target_link_libraries(
 )
 
 add_module(xrpl tx)
-target_link_libraries(xrpl.libxrpl.tx PUBLIC xrpl.libxrpl.ledger)
+# The wasm engine is a Rust crate reached over cxx: the bridge target supplies the
+# generated `lib.h` and `rust/cxx.h` that `tx/wasm` compiles against, and the Rust
+# static library everything downstream links. PUBLIC because the include path travels
+# with the module's own public headers.
+target_link_libraries(
+    xrpl.libxrpl.tx
+    PUBLIC xrpl.libxrpl.ledger xrpl_wasm_vm_ffi_cxxbridge
+)
+# Those headers do not exist at configure time, and the header-verification target
+# compiles this module's headers on their own, so both need the crates built first.
+add_dependencies(xrpl.libxrpl.tx xrpl_crates)
 
 add_module(xrpl consensus)
 target_link_libraries(
diff --git a/conan.lock b/conan.lock
index 9bedf3ac646..5b01ffbf763 100644
--- a/conan.lock
+++ b/conan.lock
@@ -3,7 +3,6 @@
     "requires": [
         "zlib/1.3.2#1cb806da49011867778ffb6ac7190fcb%1782392402.122708",
         "xxhash/0.8.3#681d36a0a6111fc56e5e45ea182c19cc%1782392402.420688",
-        "wasmi/1.0.9#1fecdab9b90c96698eb35ea99ca4f5cb%1782307153.343419",
         "sqlite3/3.53.0#324ada52333108388a9a6108bfa96734%1782392403.185447",
         "soci/4.0.3#e726491a03468795453f7c83fc924a96%1782392402.679521",
         "snappy/1.1.10#968fef506ff261592ec30c574d4a7809%1782307151.633168",
diff --git a/conanfile.py b/conanfile.py
index 77be8a24c57..2742405b6cd 100644
--- a/conanfile.py
+++ b/conanfile.py
@@ -35,7 +35,6 @@ class Xrpl(ConanFile):
         "nudb/2.0.9",
         "openssl/3.6.3",
         "soci/4.0.3",
-        "wasmi/1.0.9",
         "zlib/1.3.2",
     ]
 
@@ -224,7 +223,6 @@ def package_info(self):
             "soci::soci",
             "secp256k1::secp256k1",
             "sqlite3::sqlite",
-            "wasmi::wasmi",
             "xxhash::xxhash",
             "zlib::zlib",
         ]
diff --git a/crates/.cargo/config.toml b/crates/.cargo/config.toml
new file mode 100644
index 00000000000..57da03580bf
--- /dev/null
+++ b/crates/.cargo/config.toml
@@ -0,0 +1,5 @@
+[target.x86_64-unknown-linux-gnu]
+rustflags = ["-C", "link-args=-static-libgcc"]
+
+[target.x86_64-pc-windows-msvc]
+rustflags = ["-C", "target-feature=+crt-static"]
diff --git a/crates/CMakeLists.txt b/crates/CMakeLists.txt
new file mode 100644
index 00000000000..5ba2714a4e1
--- /dev/null
+++ b/crates/CMakeLists.txt
@@ -0,0 +1,59 @@
+set(CORROSION_VERSION 0.6.1)
+
+find_package(Corrosion ${CORROSION_VERSION} QUIET)
+if(NOT Corrosion_FOUND)
+    include(FetchContent)
+    FetchContent_Declare(
+        Corrosion
+        GIT_REPOSITORY https://github.com/corrosion-rs/corrosion.git
+        GIT_TAG v${CORROSION_VERSION}
+    )
+    FetchContent_MakeAvailable(Corrosion)
+endif()
+
+corrosion_import_crate(MANIFEST_PATH ${CMAKE_CURRENT_SOURCE_DIR}/Cargo.toml)
+
+file(
+    WRITE "${CMAKE_CURRENT_BINARY_DIR}/.clang-tidy"
+    "# Auto-generated by crates/CMakeLists.txt. Do not edit.\n"
+    "# Neutralizes clang-tidy for corrosion/cxxbridge-generated C++.\n"
+    "# One check kept enabled to avoid clang-tidy's \"no checks enabled\" error.\n"
+    "Checks: '-*,google-readability-todo'\n"
+    "WarningsAsErrors: ''\n"
+    "HeaderFilterRegex: ''\n"
+    "InheritParentConfig: false\n"
+)
+
+# Umbrella target that aggregates all crate-generated code (cxxbridge headers,
+# etc.). Build this before running clang-tidy so generated headers are present.
+add_custom_target(xrpl_crates)
+
+# add_xrpl_crate(<name> CRATE <crate> FILES <file>...) Creates a cxxbridge
+# target <name>_cxxbridge and registers it with xrpl_crates.
+function(add_xrpl_crate name)
+    cmake_parse_arguments(ARG "" "CRATE" "FILES" ${ARGN})
+    corrosion_add_cxxbridge(${name}_cxxbridge CRATE ${ARG_CRATE} FILES
+                            ${ARG_FILES}
+    )
+    # Generated cxxbridge headers don't exist at configure time; CMake 3.28+
+    # validates INTERFACE_SOURCES on consuming targets. Clear it to skip the
+    # existence check — build-time ordering is enforced by the custom commands.
+    set_target_properties(${name}_cxxbridge PROPERTIES INTERFACE_SOURCES "")
+    add_dependencies(xrpl_crates ${name}_cxxbridge)
+endfunction()
+
+add_xrpl_crate(xrpl_wasm_vm_ffi CRATE xrpl_wasm_vm_ffi FILES lib.rs)
+
+# Test-only, and deliberately not part of xrpl_wasm_vm_ffi: it carries the `wat` assembler,
+# which the engine's `wasmi default-features = false` exists to keep out of the consensus
+# path. Linked from src/tests/libxrpl only, so the shipped node cannot contain it.
+add_xrpl_crate(xrpl_wasm_testkit CRATE xrpl_wasm_testkit FILES lib.rs)
+
+# The wasm bridge `include!`s a project header, so its generated translation unit needs
+# the project's include root. Deliberately only that: a header reached from here must
+# stay light enough to compile without the Boost paths this target does not get, which
+# is why `HostContext.h` forward-declares `xrpl::HostFunctions` instead of including it.
+target_include_directories(
+    xrpl_wasm_vm_ffi_cxxbridge
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diff --git a/crates/Cargo.toml b/crates/Cargo.toml
new file mode 100644
index 00000000000..840d9a1149d
--- /dev/null
+++ b/crates/Cargo.toml
@@ -0,0 +1,15 @@
+[workspace]
+members = ["xrpl-wasm-vm-ffi", "xrpl-wasm-vm", "xrpl-wasm-testkit", "xrpl-host-functions", "xrpl-host-functions-macros"]
+resolver = "3"
+
+[workspace.dependencies]
+cxx = { version = "1.0.198", features = ["c++20"] }
+
+[workspace.package]
+edition = "2024"
+
+[profile.release]
+opt-level = 3
+overflow-checks = true
+lto = true
+debug = true
diff --git a/crates/xrpl-host-functions-macros/Cargo.toml b/crates/xrpl-host-functions-macros/Cargo.toml
new file mode 100644
index 00000000000..5b5548bec73
--- /dev/null
+++ b/crates/xrpl-host-functions-macros/Cargo.toml
@@ -0,0 +1,18 @@
+[package]
+name = "xrpl-host-functions-macros"
+version = "0.1.0"
+edition.workspace = true
+
+[lib]
+proc-macro = true
+
+[dependencies]
+syn = { version = "3", features = ["full"] }
+quote = "1"
+proc-macro2 = "1"
+
+# The expansion names `::xrpl_host_functions::HostFnSpec`, so the doctest needs the
+# facade crate. Cargo allows this cycle because dev-dependencies are outside the
+# library build graph.
+[dev-dependencies]
+xrpl-host-functions.path = "../xrpl-host-functions"
diff --git a/crates/xrpl-host-functions-macros/src/errors.rs b/crates/xrpl-host-functions-macros/src/errors.rs
new file mode 100644
index 00000000000..82d80eb56c0
--- /dev/null
+++ b/crates/xrpl-host-functions-macros/src/errors.rs
@@ -0,0 +1,12 @@
+/// Folds accumulated diagnostics into the single error a macro can return.
+///
+/// `syn::Error` is itself a collection: `combine` appends, and
+/// `into_compile_error` emits one `compile_error!` per recorded span. Folding
+/// instead of returning the first error means every mistake in a
+/// `host_functions!` block surfaces in one build rather than one per rebuild.
+pub(crate) fn combine(errors: Vec<syn::Error>) -> Option<syn::Error> {
+    errors.into_iter().reduce(|mut first, next| {
+        first.combine(next);
+        first
+    })
+}
diff --git a/crates/xrpl-host-functions-macros/src/lib.rs b/crates/xrpl-host-functions-macros/src/lib.rs
new file mode 100644
index 00000000000..80761f9420b
--- /dev/null
+++ b/crates/xrpl-host-functions-macros/src/lib.rs
@@ -0,0 +1,384 @@
+mod errors;
+mod parsed_host_function;
+
+use std::collections::HashSet;
+
+use proc_macro2::TokenStream;
+use quote::quote;
+use syn::{
+    TraitItemFn,
+    parse::{Parse, ParseStream},
+    parse2,
+};
+
+use parsed_host_function::ParsedHostFunction;
+
+/// Declares the wasm host ABI once, and generates everything that follows from it.
+///
+/// The input is a block of `fn` declarations, each carrying the gas cost the host
+/// charges before the call and the name the guest imports it under. Doc comments
+/// are kept and appear on the generated items.
+///
+/// This crate is an implementation detail of `xrpl-host-functions`, which
+/// hand-writes the types the expansion refers to and holds the one declaration
+/// block. The expansion names those types by absolute path, so a call site needs
+/// `xrpl-host-functions` as a dependency but no imports from it.
+///
+/// ```
+/// use xrpl_host_functions::HostResult;
+/// use xrpl_host_functions_macros::host_functions;
+///
+/// host_functions! {
+///     /// The sequence number of the ledger being built, as 4 little-endian bytes.
+///     #[gas = 60]
+///     #[wasm_name = "ldgr_index"]
+///     fn get_ledger_sqn(&self, out: &mut [u8]) -> HostResult<usize>;
+///
+///     /// Writes `msg` to the trace log.
+///     #[gas = 500]
+///     #[wasm_name = "trace_num"]
+///     fn trace_num(&self, msg: &str, number: i64) -> HostResult<()>;
+/// }
+///
+/// // A `HostFunctions` trait, holding the declarations verbatim:
+/// struct Host;
+/// impl HostFunctions for Host {
+///     fn get_ledger_sqn(&self, out: &mut [u8]) -> HostResult<usize> {
+///         out[..4].copy_from_slice(&7u32.to_le_bytes());
+///         Ok(4)
+///     }
+///     fn trace_num(&self, _msg: &str, _number: i64) -> HostResult<()> { Ok(()) }
+/// }
+///
+/// // A `HostFunctionSpec` enum carrying the ABI metadata as a `const` table:
+/// assert_eq!(HostFunctionSpec::GetLedgerSqn.gas(), 60);
+/// assert_eq!(HostFunctionSpec::TraceNum.wasm_name(), "trace_num");
+/// assert_eq!(HostFunctionSpec::ALL.len(), 2);
+/// ```
+///
+/// A declaration must be a plain `fn` taking `&self` and returning
+/// `HostResult<T>`, with no body and no generics: it maps to exactly one wasm
+/// import signature. Two declarations may not share a `wasm_name`, nor collapse to
+/// the same PascalCase variant.
+#[proc_macro]
+pub fn host_functions(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
+    expand(input.into())
+        .unwrap_or_else(syn::Error::into_compile_error)
+        .into()
+}
+
+fn expand(input: TokenStream) -> syn::Result<TokenStream> {
+    let HostFunctionsInput { functions } = parse2(input)?;
+
+    let mut parsed = Vec::with_capacity(functions.len());
+    let mut errors = Vec::new();
+    for function in functions {
+        match ParsedHostFunction::parse(function) {
+            Ok(function) => parsed.push(function),
+            Err(error) => errors.push(error),
+        }
+    }
+    if let Some(error) = errors::combine(errors) {
+        return Err(error);
+    }
+    if let Some(error) = errors::combine(collisions(&parsed)) {
+        return Err(error);
+    }
+
+    Ok(generate(&parsed))
+}
+
+/// Names two declarations may not share, because the generated code would then
+/// fail to compile at a span the caller cannot see.
+fn collisions(functions: &[ParsedHostFunction]) -> Vec<syn::Error> {
+    let mut errors = Vec::new();
+    let mut variants = HashSet::new();
+    let mut wasm_names = HashSet::new();
+
+    for function in functions {
+        if !variants.insert(function.variant.to_string()) {
+            errors.push(syn::Error::new_spanned(
+                &function.variant,
+                format!(
+                    "another host function already becomes the `{}` variant",
+                    function.variant
+                ),
+            ));
+        }
+        if !wasm_names.insert(function.wasm_name.value()) {
+            errors.push(syn::Error::new_spanned(
+                &function.wasm_name,
+                format!(
+                    "another host function is already imported as `{}`",
+                    function.wasm_name.value()
+                ),
+            ));
+        }
+    }
+
+    errors
+}
+
+fn generate(functions: &[ParsedHostFunction]) -> TokenStream {
+    let trait_methods = functions.iter().map(ParsedHostFunction::trait_method);
+    let variants = functions
+        .iter()
+        .map(ParsedHostFunction::variant_declaration);
+    let spec_arms = functions.iter().map(ParsedHostFunction::spec_arm);
+    let all = functions.iter().map(|function| &function.variant);
+
+    quote! {
+        /// The host side of the wasm ABI: one method per function a guest may
+        /// import.
+        ///
+        /// Implement it once per execution environment — the ledger host, a test
+        /// double, a benchmark fake — and a guest module cannot tell them apart.
+        /// Each method is one declaration from the `host_functions!` block, as
+        /// written; its `&self` receiver is not part of the ABI the guest sees,
+        /// so a host that must mutate does so behind interior mutability.
+        ///
+        /// # The output contract
+        ///
+        /// A method handed an `out` buffer **writes into it only when the whole
+        /// value fits, and returns the value's true length whether it fitted or
+        /// not.**
+        ///
+        /// The length is the value's, not the number of bytes written, because it
+        /// is how a guest that asked with too small a buffer learns the size to
+        /// ask for next time. The engine turns a length past the buffer into
+        /// `BufferTooSmall`, and one past the field cap into `DataFieldTooLarge`,
+        /// so a host needs to know neither.
+        ///
+        /// Writing nothing unless the value fits is the half only a host can hold
+        /// up. An engine can bound how many bytes are *writable* — and does, by
+        /// handing over a region clamped to the field cap — but it cannot take
+        /// back what a method already put there. A host that wrote a truncated
+        /// prefix and then reported the larger length would leave those bytes in
+        /// guest memory behind a refusal the guest is told to ignore. C++'s
+        /// `setData` is the reference point: it wrote only on a value that fit.
+        pub trait HostFunctions {
+            #(#trait_methods)*
+        }
+
+        /// One row of the ABI table: what [`HostFunctionSpec::wasm_name`] and
+        /// [`HostFunctionSpec::gas`] read from.
+        ///
+        /// Private, and the only reason it exists is to keep both of them fed
+        /// from a single `match` over the declarations.
+        struct HostFnSpec {
+            name: &'static str,
+            gas: u64,
+        }
+
+        /// Identifies one host function, and is the compile-time source of its
+        /// ABI metadata.
+        ///
+        /// One variant per `host_functions!` declaration, named by converting the
+        /// function name to PascalCase. [`Self::ALL`] is the whole ABI, which is
+        /// what a wasm engine iterates to build its import table.
+        #[derive(Debug, Clone, Copy, PartialEq, Eq)]
+        pub enum HostFunctionSpec {
+            #(#variants,)*
+        }
+
+        impl HostFunctionSpec {
+            /// Every host function, in the order declared.
+            ///
+            /// This is the complete import surface a guest may link against: a
+            /// function absent here cannot be called, and one present here must
+            /// be registered for a module that imports it to instantiate.
+            pub const ALL: &'static [Self] = &[#(Self::#all,)*];
+
+            /// This function's row of the ABI table.
+            const fn spec(self) -> HostFnSpec {
+                match self {
+                    #(#spec_arms,)*
+                }
+            }
+
+            /// The name a guest imports this function under.
+            ///
+            /// A guest's import name must match this exactly, or the module
+            /// fails to instantiate. Usable in `const` context, so import lists
+            /// can be built at compile time.
+            pub const fn wasm_name(self) -> &'static str {
+                self.spec().name
+            }
+
+            /// Gas charged before the call runs, independent of its arguments.
+            ///
+            /// Consensus-relevant: two nodes that disagree on this value
+            /// disagree on transaction outcomes. Usable in `const` context, so
+            /// gas tables can be built at compile time.
+            pub const fn gas(self) -> u64 {
+                self.spec().gas
+            }
+        }
+    }
+}
+
+struct HostFunctionsInput {
+    functions: Vec<TraitItemFn>,
+}
+
+impl Parse for HostFunctionsInput {
+    fn parse(input: ParseStream) -> syn::Result<Self> {
+        let mut functions = Vec::new();
+        while !input.is_empty() {
+            functions.push(input.parse()?);
+        }
+        Ok(HostFunctionsInput { functions })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn accepts_an_empty_block() {
+        expand(quote! {}).unwrap();
+    }
+
+    #[test]
+    fn reports_mistakes_from_every_function() {
+        let error = expand(quote! {
+            #[wasm_name = "ldgr_index"]
+            fn get_ledger_sqn(&self) -> HostResult<[u8; 4]>;
+
+            #[gas = 2000]
+            fn sha512_half(&self, data: &[u8]) -> HostResult<[u8; 32]>;
+        })
+        .expect_err("expected parsing to fail");
+
+        let messages: Vec<_> = error.into_iter().map(|error| error.to_string()).collect();
+        assert_eq!(messages.len(), 2, "{messages:?}");
+        assert!(messages[0].contains("missing `#[gas"), "{messages:?}");
+        assert!(messages[1].contains("missing `#[wasm_name"), "{messages:?}");
+    }
+
+    #[test]
+    fn propagates_syntax_errors() {
+        let error = expand(quote! { fn missing_semicolon() }).expect_err("expected a syntax error");
+        assert!(!error.to_string().is_empty());
+    }
+
+    /// The messages of every diagnostic recorded by one failed `expand`.
+    fn messages(input: TokenStream) -> Vec<String> {
+        let Err(error) = expand(input) else {
+            panic!("expected expansion to fail");
+        };
+        error.into_iter().map(|error| error.to_string()).collect()
+    }
+
+    #[test]
+    fn generates_the_trait_the_enum_and_the_table() {
+        let generated = expand(quote! {
+            #[gas = 60]
+            #[wasm_name = "ldgr_index"]
+            fn get_ledger_sqn(&self) -> HostResult<[u8; 4]>;
+
+            #[gas = 500]
+            #[wasm_name = "trace_num"]
+            fn trace_num(&self, msg: &str, number: i64) -> HostResult<()>;
+        })
+        .unwrap()
+        .to_string();
+
+        for expected in [
+            "pub trait HostFunctions",
+            "fn get_ledger_sqn (& self) -> HostResult < [u8 ; 4] > ;",
+            "fn trace_num (& self , msg : & str , number : i64) -> HostResult < () > ;",
+            "pub enum HostFunctionSpec { GetLedgerSqn , TraceNum , }",
+            "pub const ALL : & 'static [Self] = & [Self :: GetLedgerSqn , Self :: TraceNum ,]",
+            // The table's row type is generated too, and stays private.
+            "struct HostFnSpec { name : & 'static str , gas : u64 , }",
+            "const fn spec (self) -> HostFnSpec",
+            "Self :: GetLedgerSqn => HostFnSpec { name : \"ldgr_index\" , gas : 60u64 }",
+            "pub const fn wasm_name (self) -> & 'static str",
+            "pub const fn gas (self) -> u64",
+        ] {
+            assert!(generated.contains(expected), "missing {expected:?}");
+        }
+    }
+
+    /// The expansion stands alone: every name in it is either generated here or
+    /// written in the declarations, so it cannot depend on the crate it lands in.
+    #[test]
+    fn names_no_crate_of_its_own() {
+        let generated = expand(quote! {
+            #[gas = 60]
+            #[wasm_name = "ldgr_index"]
+            fn get_ledger_sqn(&self) -> HostResult<[u8; 4]>;
+        })
+        .unwrap()
+        .to_string();
+
+        assert!(!generated.contains("xrpl_host_functions"), "{generated}");
+
+        // `Self::Variant` is the only path the expansion may build: anything else
+        // would reach out of the generated code. Doc comments spell paths without
+        // spaces (`Self::ALL`), so they do not match.
+        for (index, _) in generated.match_indices(" :: ") {
+            assert!(
+                generated[..index].ends_with("Self"),
+                "path out of the expansion at {index}: {generated}"
+            );
+        }
+    }
+
+    /// `spec` is an implementation detail of the two accessors, so it must not
+    /// become part of the ABI crate's public surface.
+    #[test]
+    fn keeps_the_table_row_private() {
+        let generated = expand(quote! {
+            #[gas = 60]
+            #[wasm_name = "ldgr_index"]
+            fn get_ledger_sqn(&self) -> HostResult<[u8; 4]>;
+        })
+        .unwrap()
+        .to_string();
+
+        assert!(!generated.contains("pub struct HostFnSpec"), "{generated}");
+        assert!(!generated.contains("pub const fn spec"), "{generated}");
+    }
+
+    #[test]
+    fn rejects_two_functions_that_share_a_wasm_name() {
+        let messages = messages(quote! {
+            #[gas = 60]
+            #[wasm_name = "trace"]
+            fn trace(&self, msg: &str) -> HostResult<()>;
+
+            #[gas = 70]
+            #[wasm_name = "trace"]
+            fn trace_num(&self, msg: &str, number: i64) -> HostResult<()>;
+        });
+
+        assert_eq!(messages.len(), 1, "{messages:?}");
+        assert!(
+            messages[0].contains("already imported as `trace`"),
+            "{messages:?}"
+        );
+    }
+
+    /// Names that differ only in underscores collapse to one enum variant.
+    #[test]
+    fn rejects_two_functions_that_share_a_variant() {
+        let messages = messages(quote! {
+            #[gas = 60]
+            #[wasm_name = "a"]
+            fn get_ledger_sqn(&self) -> HostResult<[u8; 4]>;
+
+            #[gas = 70]
+            #[wasm_name = "b"]
+            fn get_ledger__sqn(&self) -> HostResult<[u8; 4]>;
+        });
+
+        assert_eq!(messages.len(), 1, "{messages:?}");
+        assert!(
+            messages[0].contains("`GetLedgerSqn` variant"),
+            "{messages:?}"
+        );
+    }
+}
diff --git a/crates/xrpl-host-functions-macros/src/parsed_host_function.rs b/crates/xrpl-host-functions-macros/src/parsed_host_function.rs
new file mode 100644
index 00000000000..813dbc5efc3
--- /dev/null
+++ b/crates/xrpl-host-functions-macros/src/parsed_host_function.rs
@@ -0,0 +1,871 @@
+use proc_macro2::TokenStream;
+use quote::{format_ident, quote};
+use syn::{
+    Attribute, Expr, ExprLit, Ident, Lit, LitStr, PathArguments, ReceiverKind, ReturnType, Safety,
+    Signature, TraitItemFn, Type, TypePath,
+};
+
+use crate::errors;
+
+/// `#[gas = N]`: the base gas charged before the call runs.
+const GAS: &str = "gas";
+/// `#[wasm_name = "..."]`: the name the guest imports the function under.
+const WASM_NAME: &str = "wasm_name";
+/// `///` desugars to `#[doc = "..."]` before macro expansion.
+const DOC: &str = "doc";
+/// The alias every declaration returns its success type through.
+const HOST_RESULT: &str = "HostResult";
+
+/// One entry of a `host_functions!` block: its ABI metadata and its signature.
+pub(crate) struct ParsedHostFunction {
+    pub(crate) gas: u64,
+    /// Kept as the literal the user wrote, so diagnostics and the generated
+    /// string both carry that span.
+    pub(crate) wasm_name: LitStr,
+    /// Doc comments, in source order, to re-emit on the generated items.
+    pub(crate) docs: Vec<Attribute>,
+    /// The enum variant this declaration becomes, spanned at the function name.
+    pub(crate) variant: Ident,
+    pub(crate) signature: Signature,
+}
+
+impl ParsedHostFunction {
+    /// `#[doc …] fn get_ledger_sqn(&self) -> HostResult<[u8; 4]>;`
+    pub(crate) fn trait_method(&self) -> TokenStream {
+        let docs = &self.docs;
+        // The declaration is already a trait method: emitted verbatim, so what
+        // the block reads like is what the trait is.
+        let signature = &self.signature;
+
+        quote! {
+            #(#docs)*
+            #signature;
+        }
+    }
+
+    /// `#[doc …] GetLedgerSqn`
+    pub(crate) fn variant_declaration(&self) -> TokenStream {
+        let docs = &self.docs;
+        let variant = &self.variant;
+        quote! {
+            #(#docs)*
+            #variant
+        }
+    }
+
+    /// `Self::GetLedgerSqn => HostFnSpec { name: "ldgr_index", gas: 60u64 }`
+    pub(crate) fn spec_arm(&self) -> TokenStream {
+        let Self {
+            gas,
+            wasm_name,
+            variant,
+            ..
+        } = self;
+        quote! {
+            Self::#variant => HostFnSpec { name: #wasm_name, gas: #gas }
+        }
+    }
+
+    pub(crate) fn parse(function: TraitItemFn) -> syn::Result<Self> {
+        let mut gas = None;
+        let mut wasm_name = None;
+        let mut docs = Vec::new();
+        let mut errors = Vec::new();
+
+        // Tracked separately from `gas`/`wasm_name` so a malformed attribute is
+        // not also reported as a missing one.
+        let mut saw_gas = false;
+        let mut saw_wasm_name = false;
+
+        for attr in function.attrs {
+            if attr.path().is_ident(GAS) {
+                saw_gas = true;
+                if let Err(error) = int_value(&attr).and_then(|v| set_once(&mut gas, v, &attr)) {
+                    errors.push(error);
+                }
+            } else if attr.path().is_ident(WASM_NAME) {
+                saw_wasm_name = true;
+                if let Err(error) =
+                    string_value(&attr).and_then(|v| set_once(&mut wasm_name, v, &attr))
+                {
+                    errors.push(error);
+                }
+            } else if attr.path().is_ident(DOC) {
+                docs.push(attr);
+            } else {
+                errors.push(syn::Error::new_spanned(
+                    &attr,
+                    format!("unexpected attribute `{}`", path_name(&attr)),
+                ));
+            }
+        }
+
+        if !saw_gas {
+            errors.push(syn::Error::new_spanned(
+                &function.sig.ident,
+                format!("missing `#[{GAS} = ...]` attribute"),
+            ));
+        }
+        if !saw_wasm_name {
+            errors.push(syn::Error::new_spanned(
+                &function.sig.ident,
+                format!("missing `#[{WASM_NAME} = \"...\"]` attribute"),
+            ));
+        }
+        if let Some(body) = &function.default {
+            errors.push(syn::Error::new_spanned(
+                body,
+                "a host function is implemented by the host, so it must not have a body",
+            ));
+        }
+        if !function.sig.generics.params.is_empty() || function.sig.generics.where_clause.is_some()
+        {
+            errors.push(syn::Error::new_spanned(
+                &function.sig.ident,
+                "a host function must not be generic: it maps to one wasm import signature",
+            ));
+        }
+        errors.extend(check_receiver(&function.sig).err());
+        errors.extend(check_return_type(&function.sig).err());
+        if let Some(name) = &wasm_name {
+            errors.extend(check_wasm_name(name).err());
+        }
+        reject_modifiers(&function.sig, &mut errors);
+
+        // A name whose PascalCase form is not a legal variant is reported here
+        // rather than emitted, which would either panic or fail downstream.
+        let variant = match variant_ident(&function.sig.ident) {
+            Ok(variant) => Some(variant),
+            Err(error) => {
+                errors.push(error);
+                None
+            }
+        };
+
+        if let Some(error) = errors::combine(errors) {
+            return Err(error);
+        }
+
+        let (Some(gas), Some(wasm_name), Some(variant)) = (gas, wasm_name, variant) else {
+            unreachable!("every absent field is reported above");
+        };
+
+        Ok(Self {
+            gas,
+            wasm_name,
+            docs,
+            variant,
+            signature: function.sig,
+        })
+    }
+}
+
+/// Every declaration carries a receiver, and it is always `&self`.
+///
+/// `&self` is the only receiver that can work: the VM reaches the host through a
+/// shared `&dyn HostFunctions` stored in the wasmi `Store`, and a host that needs
+/// to mutate does so behind interior mutability. The receiver is not part of the
+/// wasm ABI — the guest passes no `self` — so it is uniform across the block.
+fn check_receiver(signature: &Signature) -> syn::Result<()> {
+    let Some(receiver) = signature.receiver() else {
+        return Err(syn::Error::new_spanned(
+            &signature.ident,
+            format!(
+                "a host function must declare its receiver: `fn {}(&self, ...)`",
+                signature.ident
+            ),
+        ));
+    };
+
+    // `&self` and nothing else: not `&mut self`, not `self`/`mut self`, not a
+    // typed `self: Box<Self>`, and not a spelled-out lifetime.
+    if !matches!(receiver.kind, ReceiverKind::Reference(_, None, None)) {
+        return Err(syn::Error::new_spanned(
+            receiver,
+            "a host function's receiver must be exactly `&self`: the VM calls the host \
+             through a shared `&dyn HostFunctions`",
+        ));
+    }
+    Ok(())
+}
+
+/// Every declaration returns `HostResult<T>`, including the ones that yield
+/// nothing (`HostResult<()>`).
+///
+/// One shape for every function is what lets a single dispatch adapter lower them
+/// all: lift the arguments out of guest memory, call the host, then turn `Ok(T)`
+/// into the wire's non-negative `i32` and `Err(e)` into a negative code or a trap.
+/// A function returning a bare `T` would need its own arm.
+fn check_return_type(signature: &Signature) -> syn::Result<()> {
+    const SHAPE: &str = "a host function must return `HostResult<T>` — \
+                         `HostResult<()>` if it yields nothing";
+
+    let ReturnType::Type(_, returned) = &signature.output else {
+        return Err(syn::Error::new_spanned(&signature.ident, SHAPE));
+    };
+
+    let Type::Path(TypePath {
+        qself: None, path, ..
+    }) = &**returned
+    else {
+        return Err(syn::Error::new_spanned(returned, SHAPE));
+    };
+    // The last segment only, so `HostResult<T>` may be written qualified.
+    let Some(last) = path.segments.last() else {
+        return Err(syn::Error::new_spanned(returned, SHAPE));
+    };
+    if last.ident != HOST_RESULT {
+        return Err(syn::Error::new_spanned(returned, SHAPE));
+    }
+
+    // `HostResult` without its success type is `HostResult` the alias, which names
+    // no type; rustc's own message for that is unhelpfully far from the cause.
+    let PathArguments::AngleBracketed(arguments) = &last.arguments else {
+        return Err(syn::Error::new_spanned(
+            returned,
+            format!("`{HOST_RESULT}` needs its success type: `{HOST_RESULT}<T>`"),
+        ));
+    };
+    if arguments.args.len() != 1 {
+        return Err(syn::Error::new_spanned(
+            arguments,
+            format!("`{HOST_RESULT}` takes exactly one type: `{HOST_RESULT}<T>`"),
+        ));
+    }
+    Ok(())
+}
+
+/// `const`, `async`, `unsafe`/`safe` and `extern "…"` have no meaning in the
+/// wasm ABI, and would otherwise pass silently into the generated trait.
+fn reject_modifiers(signature: &Signature, errors: &mut Vec<syn::Error>) {
+    const PLAIN: &str =
+        "a host function must be a plain `fn`: this modifier is not part of the wasm ABI";
+
+    if let Some(constness) = &signature.constness {
+        errors.push(syn::Error::new_spanned(constness, PLAIN));
+    }
+    if let Some(asyncness) = &signature.asyncness {
+        errors.push(syn::Error::new_spanned(asyncness, PLAIN));
+    }
+    match &signature.safety {
+        Safety::Default => {}
+        Safety::Safe(token) => errors.push(syn::Error::new_spanned(token, PLAIN)),
+        Safety::Unsafe(token) => errors.push(syn::Error::new_spanned(token, PLAIN)),
+    }
+    if let Some(abi) = &signature.abi {
+        errors.push(syn::Error::new_spanned(abi, PLAIN));
+    }
+}
+
+/// The wasm import name reaches the engine's import table verbatim, so it is
+/// held to what an import name can sanely be rather than to any string.
+fn check_wasm_name(name: &LitStr) -> syn::Result<()> {
+    let value = name.value();
+    if value.is_empty() {
+        return Err(syn::Error::new_spanned(
+            name,
+            "the wasm name must not be empty",
+        ));
+    }
+    if let Some(character) = value
+        .chars()
+        .find(|c| !c.is_ascii_alphanumeric() && *c != '_')
+    {
+        return Err(syn::Error::new_spanned(
+            name,
+            format!(
+                "a wasm name may only contain `A-Za-z0-9_`, but this one contains {character:?}"
+            ),
+        ));
+    }
+    Ok(())
+}
+
+/// The enum variant a declaration becomes: `get_ledger_sqn` -> `GetLedgerSqn`.
+///
+/// The result carries `ident`'s span, so anything the compiler says about the
+/// variant points at the declaration that produced it.
+fn variant_ident(ident: &Ident) -> syn::Result<Ident> {
+    // `to_string` spells raw identifiers `r#type`; the `r#` is not part of the name.
+    let name = ident.to_string();
+    let name = name.strip_prefix("r#").unwrap_or(&name);
+
+    let mut pascal = String::with_capacity(name.len());
+    let mut capitalize = true;
+    for character in name.chars() {
+        if character == '_' {
+            capitalize = true;
+        } else if capitalize {
+            pascal.extend(character.to_uppercase());
+            capitalize = false;
+        } else {
+            pascal.push(character);
+        }
+    }
+
+    // A name of nothing but underscores leaves `pascal` empty; the original is
+    // already a legal identifier, so keep it.
+    if pascal.is_empty() {
+        return Ok(ident.clone());
+    }
+
+    // `Ident::new` panics on a leading digit (`_2fa` -> `2fa`) and silently
+    // accepts keyword spellings (`self_` -> `Self`), which then fails to parse
+    // where the variant is emitted. Parsing rejects both, without panicking.
+    if let Err(error) = syn::parse_str::<Ident>(&pascal) {
+        return Err(syn::Error::new_spanned(
+            ident,
+            format!(
+                "this name becomes the enum variant `{pascal}`, which is not a valid \
+                 variant name ({error}); rename the host function"
+            ),
+        ));
+    }
+    Ok(format_ident!("{pascal}", span = ident.span()))
+}
+
+/// Records `value`, or reports that the attribute appeared more than once.
+fn set_once<T>(slot: &mut Option<T>, value: T, attr: &Attribute) -> syn::Result<()> {
+    if slot.replace(value).is_some() {
+        return Err(syn::Error::new_spanned(
+            attr,
+            format!("duplicate `{}` attribute", path_name(attr)),
+        ));
+    }
+    Ok(())
+}
+
+fn int_value(attr: &Attribute) -> syn::Result<u64> {
+    match &attr.meta.require_name_value()?.value {
+        Expr::Lit(ExprLit {
+            lit: Lit::Int(int), ..
+        }) => {
+            // `LitInt` keeps the sign in its digits, so `base10_parse::<u64>`
+            // would report a negative value as "invalid digit found in string".
+            if int.base10_digits().starts_with('-') {
+                return Err(syn::Error::new_spanned(
+                    int,
+                    format!("`{}` must not be negative", path_name(attr)),
+                ));
+            }
+            int.base10_parse()
+        }
+        other => Err(syn::Error::new_spanned(
+            other,
+            format!("`{}` expects an integer literal", path_name(attr)),
+        )),
+    }
+}
+
+fn string_value(attr: &Attribute) -> syn::Result<LitStr> {
+    match &attr.meta.require_name_value()?.value {
+        Expr::Lit(ExprLit {
+            lit: Lit::Str(string),
+            ..
+        }) => Ok(string.clone()),
+        other => Err(syn::Error::new_spanned(
+            other,
+            format!("`{}` expects a string literal", path_name(attr)),
+        )),
+    }
+}
+
+/// The attribute's path as written, for diagnostics: `gas`, or `foo::bar`.
+fn path_name(attr: &Attribute) -> String {
+    attr.path()
+        .segments
+        .iter()
+        .map(|segment| segment.ident.to_string())
+        .collect::<Vec<_>>()
+        .join("::")
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use quote::ToTokens;
+    use syn::parse_quote;
+
+    /// The message of every diagnostic recorded by one failed `parse`.
+    ///
+    /// `expect_err` is unavailable here: it needs `T: Debug`, and syn only
+    /// implements `Debug` for its AST types under the `extra-traits` feature.
+    fn messages(function: TraitItemFn) -> Vec<String> {
+        let Err(error) = ParsedHostFunction::parse(function) else {
+            panic!("expected parsing to fail");
+        };
+        error.into_iter().map(|error| error.to_string()).collect()
+    }
+
+    fn doc_text(attr: &Attribute) -> String {
+        match &attr.meta.require_name_value().unwrap().value {
+            Expr::Lit(ExprLit {
+                lit: Lit::Str(text),
+                ..
+            }) => text.value(),
+            _ => panic!("doc attribute is not a string literal"),
+        }
+    }
+
+    #[test]
+    fn reads_gas_and_wasm_name() {
+        let parsed = ParsedHostFunction::parse(parse_quote! {
+            #[gas = 60]
+            #[wasm_name = "ldgr_index"]
+            fn get_ledger_sqn(&self) -> HostResult<[u8; 4]>;
+        })
+        .unwrap();
+
+        assert_eq!(parsed.gas, 60);
+        assert_eq!(parsed.wasm_name.value(), "ldgr_index");
+        assert_eq!(parsed.signature.ident.to_string(), "get_ledger_sqn");
+        assert_eq!(parsed.variant.to_string(), "GetLedgerSqn");
+        assert!(parsed.docs.is_empty());
+    }
+
+    #[test]
+    fn derives_variant_names_from_function_names() {
+        for (function, variant) in [
+            ("get_ledger_sqn", "GetLedgerSqn"),
+            ("sha512_half", "Sha512Half"),
+            ("trace", "Trace"),
+            ("get_current_ledger_obj_field", "GetCurrentLedgerObjField"),
+            ("r#type", "Type"),
+            ("trace2", "Trace2"),
+            // Pathological, but must not panic: no letters to capitalize.
+            ("__", "__"),
+        ] {
+            let ident = format_ident!("{function}");
+            assert_eq!(
+                variant_ident(&ident).map(|v| v.to_string()).ok(),
+                Some(variant.to_owned()),
+                "{function}"
+            );
+        }
+    }
+
+    /// `_2fa` would PascalCase to `2fa`; building that `Ident` panics, and a
+    /// panic in a proc macro is reported with no useful span at all.
+    #[test]
+    fn rejects_a_name_that_becomes_a_leading_digit() {
+        let messages = messages(parse_quote! {
+            #[gas = 60]
+            #[wasm_name = "two_factor"]
+            fn _2fa(&self) -> HostResult<()>;
+        });
+
+        assert_eq!(messages.len(), 1, "{messages:?}");
+        assert!(
+            messages[0].contains("becomes the enum variant `2fa`"),
+            "{messages:?}"
+        );
+    }
+
+    /// `self_` PascalCases to `Self`, which `Ident::new` accepts and rustc then
+    /// rejects where the variant is emitted. `r#Self` is not a legal escape.
+    #[test]
+    fn rejects_a_name_that_becomes_a_keyword() {
+        for function in ["self_", "_self"] {
+            let ident = format_ident!("{function}");
+            let Err(error) = variant_ident(&ident) else {
+                panic!("expected `{function}` to be rejected");
+            };
+            assert!(
+                error.to_string().contains("variant `Self`"),
+                "{}",
+                error.to_string()
+            );
+        }
+    }
+
+    #[test]
+    fn rejects_negative_gas() {
+        let messages = messages(parse_quote! {
+            #[gas = -5]
+            #[wasm_name = "ldgr_index"]
+            fn get_ledger_sqn(&self) -> HostResult<[u8; 4]>;
+        });
+
+        assert_eq!(messages.len(), 1, "{messages:?}");
+        assert_eq!(messages[0], "`gas` must not be negative");
+    }
+
+    #[test]
+    fn rejects_unusable_wasm_names() {
+        let empty = messages(parse_quote! {
+            #[gas = 60]
+            #[wasm_name = ""]
+            fn get_ledger_sqn(&self) -> HostResult<[u8; 4]>;
+        });
+        assert_eq!(empty.len(), 1, "{empty:?}");
+        assert_eq!(empty[0], "the wasm name must not be empty");
+
+        let spaced = messages(parse_quote! {
+            #[gas = 60]
+            #[wasm_name = "ldgr index"]
+            fn get_ledger_sqn(&self) -> HostResult<[u8; 4]>;
+        });
+        assert_eq!(spaced.len(), 1, "{spaced:?}");
+        assert!(spaced[0].contains("may only contain"), "{spaced:?}");
+    }
+
+    #[test]
+    fn rejects_signature_modifiers() {
+        for declaration in [
+            quote! { unsafe fn get_ledger_sqn(&self) -> HostResult<[u8; 4]>; },
+            quote! { async fn get_ledger_sqn(&self) -> HostResult<[u8; 4]>; },
+            quote! { const fn get_ledger_sqn(&self) -> HostResult<[u8; 4]>; },
+            quote! { extern "C" fn get_ledger_sqn(&self) -> HostResult<[u8; 4]>; },
+        ] {
+            let function: TraitItemFn = syn::parse2(quote! {
+                #[gas = 60]
+                #[wasm_name = "ldgr_index"]
+                #declaration
+            })
+            .unwrap();
+
+            let messages = messages(function);
+            assert_eq!(messages.len(), 1, "{messages:?}");
+            assert!(messages[0].contains("must be a plain `fn`"), "{messages:?}");
+        }
+    }
+
+    #[test]
+    fn trait_method_keeps_the_declared_receiver_and_ends_in_a_semicolon() {
+        let parsed = ParsedHostFunction::parse(parse_quote! {
+            /// Hashes `data`.
+            #[gas = 2000]
+            #[wasm_name = "sha512_half"]
+            fn sha512_half(&self, data: &[u8]) -> HostResult<[u8; 32]>;
+        })
+        .unwrap();
+
+        // `///` reaches the macro as `#[doc = r"..."]`: rustc's lexer spells doc
+        // comments as raw string literals.
+        let method = parsed.trait_method().to_string();
+        assert!(
+            method.starts_with("# [doc = r\" Hashes `data`.\"]"),
+            "{method}"
+        );
+        assert!(
+            method
+                .contains("fn sha512_half (& self , data : & [u8]) -> HostResult < [u8 ; 32] > ;"),
+            "{method}"
+        );
+    }
+
+    #[test]
+    fn spec_arm_carries_the_name_and_the_gas() {
+        let parsed = ParsedHostFunction::parse(parse_quote! {
+            #[gas = 60]
+            #[wasm_name = "ldgr_index"]
+            fn get_ledger_sqn(&self) -> HostResult<[u8; 4]>;
+        })
+        .unwrap();
+
+        assert_eq!(
+            parsed.spec_arm().to_string(),
+            "Self :: GetLedgerSqn => HostFnSpec { name : \"ldgr_index\" , gas : 60u64 }"
+        );
+    }
+
+    #[test]
+    fn keeps_doc_comments_in_source_order() {
+        let parsed = ParsedHostFunction::parse(parse_quote! {
+            /// First line.
+            ///
+            /// Third line.
+            #[gas = 60]
+            #[wasm_name = "ldgr_index"]
+            fn get_ledger_sqn(&self) -> HostResult<[u8; 4]>;
+        })
+        .unwrap();
+
+        let docs: Vec<_> = parsed.docs.iter().map(doc_text).collect();
+        assert_eq!(docs, vec![" First line.", "", " Third line."]);
+    }
+
+    #[test]
+    fn preserves_parameters_and_return_type() {
+        let traced = ParsedHostFunction::parse(parse_quote! {
+            #[gas = 500]
+            #[wasm_name = "trace"]
+            fn trace(&self, msg: &str, data: &[u8], as_hex: bool) -> HostResult<()>;
+        })
+        .unwrap();
+        // The receiver is `inputs[0]`; the three wasm parameters follow it.
+        assert_eq!(traced.signature.inputs.len(), 4);
+        assert_eq!(
+            traced.signature.output.to_token_stream().to_string(),
+            "-> HostResult < () >"
+        );
+
+        let hashed = ParsedHostFunction::parse(parse_quote! {
+            #[gas = 2000]
+            #[wasm_name = "sha512_half"]
+            fn sha512_half(&self, data: &[u8]) -> HostResult<[u8; HASH_LEN]>;
+        })
+        .unwrap();
+        assert_eq!(
+            hashed.signature.output.to_token_stream().to_string(),
+            "-> HostResult < [u8 ; HASH_LEN] >"
+        );
+    }
+
+    #[test]
+    fn reports_both_missing_attributes_at_once() {
+        let messages = messages(parse_quote! {
+            fn get_ledger_sqn(&self) -> HostResult<[u8; 4]>;
+        });
+
+        assert_eq!(messages.len(), 2);
+        assert!(messages[0].contains("missing `#[gas"), "{messages:?}");
+        assert!(messages[1].contains("missing `#[wasm_name"), "{messages:?}");
+    }
+
+    #[test]
+    fn names_the_unexpected_attribute() {
+        let messages = messages(parse_quote! {
+            #[gas = 60]
+            #[wsam_name = "typo"]
+            fn get_ledger_sqn(&self) -> HostResult<[u8; 4]>;
+        });
+
+        // The typo'd attribute, plus the `wasm_name` it failed to be.
+        assert_eq!(messages.len(), 2);
+        assert!(
+            messages.iter().any(|m| m.contains("`wsam_name`")),
+            "{messages:?}"
+        );
+    }
+
+    #[test]
+    fn rejects_wrong_literal_types() {
+        let gas = messages(parse_quote! {
+            #[gas = "60"]
+            #[wasm_name = "ldgr_index"]
+            fn get_ledger_sqn(&self) -> HostResult<[u8; 4]>;
+        });
+        assert_eq!(gas.len(), 1, "{gas:?}");
+        assert!(
+            gas[0].contains("`gas` expects an integer literal"),
+            "{gas:?}"
+        );
+
+        let name = messages(parse_quote! {
+            #[gas = 60]
+            #[wasm_name = 7]
+            fn get_ledger_sqn(&self) -> HostResult<[u8; 4]>;
+        });
+        assert_eq!(name.len(), 1, "{name:?}");
+        assert!(
+            name[0].contains("`wasm_name` expects a string literal"),
+            "{name:?}"
+        );
+    }
+
+    #[test]
+    fn rejects_gas_that_does_not_fit_in_u64() {
+        let messages = messages(parse_quote! {
+            #[gas = 99999999999999999999999]
+            #[wasm_name = "ldgr_index"]
+            fn get_ledger_sqn(&self) -> HostResult<[u8; 4]>;
+        });
+
+        assert_eq!(messages.len(), 1, "{messages:?}");
+        assert!(messages[0].contains("number too large"), "{messages:?}");
+    }
+
+    #[test]
+    fn rejects_attribute_shapes_other_than_name_value() {
+        let bare = messages(parse_quote! {
+            #[gas]
+            #[wasm_name = "ldgr_index"]
+            fn get_ledger_sqn(&self) -> HostResult<[u8; 4]>;
+        });
+        assert_eq!(bare.len(), 1, "{bare:?}");
+        assert!(bare[0].contains("gas = ..."), "{bare:?}");
+
+        let list = messages(parse_quote! {
+            #[gas(60)]
+            #[wasm_name = "ldgr_index"]
+            fn get_ledger_sqn(&self) -> HostResult<[u8; 4]>;
+        });
+        assert_eq!(list.len(), 1, "{list:?}");
+    }
+
+    #[test]
+    fn rejects_duplicate_attributes() {
+        let messages = messages(parse_quote! {
+            #[gas = 60]
+            #[gas = 70]
+            #[wasm_name = "ldgr_index"]
+            #[wasm_name = "ldgr_index"]
+            fn get_ledger_sqn(&self) -> HostResult<[u8; 4]>;
+        });
+
+        assert_eq!(messages.len(), 2, "{messages:?}");
+        assert!(messages[0].contains("duplicate `gas`"), "{messages:?}");
+        assert!(
+            messages[1].contains("duplicate `wasm_name`"),
+            "{messages:?}"
+        );
+    }
+
+    /// A malformed attribute must not also be reported as an absent one.
+    #[test]
+    fn does_not_report_a_malformed_attribute_as_missing() {
+        let messages = messages(parse_quote! {
+            #[gas = "60"]
+            #[wasm_name = 7]
+            fn get_ledger_sqn(&self) -> HostResult<[u8; 4]>;
+        });
+
+        assert_eq!(messages.len(), 2, "{messages:?}");
+        assert!(
+            !messages.iter().any(|m| m.contains("missing")),
+            "{messages:?}"
+        );
+    }
+
+    #[test]
+    fn rejects_a_body() {
+        let messages = messages(parse_quote! {
+            #[gas = 60]
+            #[wasm_name = "ldgr_index"]
+            fn get_ledger_sqn(&self) -> HostResult<[u8; 4]> { Ok([0; 4]) }
+        });
+
+        assert_eq!(messages.len(), 1, "{messages:?}");
+        assert!(messages[0].contains("must not have a body"), "{messages:?}");
+    }
+
+    #[test]
+    fn rejects_generics() {
+        let parameter = messages(parse_quote! {
+            #[gas = 60]
+            #[wasm_name = "ldgr_index"]
+            fn get_ledger_sqn<T>(&self) -> HostResult<T>;
+        });
+        assert_eq!(parameter.len(), 1, "{parameter:?}");
+        assert!(
+            parameter[0].contains("must not be generic"),
+            "{parameter:?}"
+        );
+
+        let clause = messages(parse_quote! {
+            #[gas = 60]
+            #[wasm_name = "ldgr_index"]
+            fn get_ledger_sqn(&self) -> HostResult<[u8; 4]> where Self: Sized;
+        });
+        assert_eq!(clause.len(), 1, "{clause:?}");
+    }
+
+    #[test]
+    fn requires_a_receiver() {
+        let messages = messages(parse_quote! {
+            #[gas = 60]
+            #[wasm_name = "ldgr_index"]
+            fn get_ledger_sqn() -> HostResult<[u8; 4]>;
+        });
+
+        assert_eq!(messages.len(), 1, "{messages:?}");
+        assert!(
+            messages[0].contains("must declare its receiver: `fn get_ledger_sqn(&self, ...)`"),
+            "{messages:?}"
+        );
+    }
+
+    /// Anything but `&self` would need a host the VM cannot hand out: it holds
+    /// one shared `&dyn HostFunctions` for the whole run.
+    #[test]
+    fn rejects_receivers_other_than_shared_self() {
+        for receiver in [
+            quote! { &mut self },
+            quote! { self },
+            quote! { mut self },
+            quote! { self: Box<Self> },
+            quote! { &'a self },
+        ] {
+            let function: TraitItemFn = syn::parse2(quote! {
+                #[gas = 60]
+                #[wasm_name = "ldgr_index"]
+                fn get_ledger_sqn(#receiver) -> HostResult<[u8; 4]>;
+            })
+            .unwrap_or_else(|_| panic!("`{receiver}` should parse"));
+
+            let messages = messages(function);
+            assert_eq!(messages.len(), 1, "`{receiver}`: {messages:?}");
+            assert!(
+                messages[0].contains("must be exactly `&self`"),
+                "`{receiver}`: {messages:?}"
+            );
+        }
+    }
+
+    /// A bare `T` return would need its own lowering arm, so the uniform shape is
+    /// required rather than inferred.
+    #[test]
+    fn rejects_returns_that_are_not_host_result() {
+        for output in [
+            quote! {},
+            quote! { -> () },
+            quote! { -> [u8; 4] },
+            quote! { -> i32 },
+            quote! { -> Result<[u8; 4], HostError> },
+            quote! { -> impl Iterator<Item = u8> },
+        ] {
+            let function: TraitItemFn = syn::parse2(quote! {
+                #[gas = 60]
+                #[wasm_name = "ldgr_index"]
+                fn get_ledger_sqn(&self) #output;
+            })
+            .unwrap_or_else(|_| panic!("`{output}` should parse"));
+
+            let messages = messages(function);
+            assert_eq!(messages.len(), 1, "`{output}`: {messages:?}");
+            assert!(
+                messages[0].contains("must return `HostResult<T>`"),
+                "`{output}`: {messages:?}"
+            );
+        }
+    }
+
+    /// `HostResult` may be written qualified, since the trait method keeps whatever
+    /// path resolves where the block is written.
+    #[test]
+    fn accepts_a_qualified_host_result() {
+        let parsed = ParsedHostFunction::parse(parse_quote! {
+            #[gas = 60]
+            #[wasm_name = "ldgr_index"]
+            fn get_ledger_sqn(&self) -> xrpl_host_functions::HostResult<[u8; 4]>;
+        })
+        .unwrap();
+
+        assert!(
+            parsed
+                .trait_method()
+                .to_string()
+                .contains("xrpl_host_functions :: HostResult < [u8 ; 4] >"),
+            "{}",
+            parsed.trait_method()
+        );
+    }
+
+    /// `HostResult` with no success type names no type at all; rustc's own error
+    /// for that lands on the generated trait, far from the declaration.
+    #[test]
+    fn rejects_host_result_without_a_success_type() {
+        let messages = messages(parse_quote! {
+            #[gas = 60]
+            #[wasm_name = "ldgr_index"]
+            fn get_ledger_sqn(&self) -> HostResult;
+        });
+
+        assert_eq!(messages.len(), 1, "{messages:?}");
+        assert!(
+            messages[0].contains("needs its success type"),
+            "{messages:?}"
+        );
+    }
+}
diff --git a/crates/xrpl-host-functions/Cargo.toml b/crates/xrpl-host-functions/Cargo.toml
new file mode 100644
index 00000000000..c08bb7d62f5
--- /dev/null
+++ b/crates/xrpl-host-functions/Cargo.toml
@@ -0,0 +1,7 @@
+[package]
+name = "xrpl-host-functions"
+version = "0.1.0"
+edition.workspace = true
+
+[dependencies]
+xrpl-host-functions-macros.path = "../xrpl-host-functions-macros"
diff --git a/crates/xrpl-host-functions/src/lib.rs b/crates/xrpl-host-functions/src/lib.rs
new file mode 100644
index 00000000000..80d104301b2
--- /dev/null
+++ b/crates/xrpl-host-functions/src/lib.rs
@@ -0,0 +1,190 @@
+//! The wasm host ABI: the one place it is declared.
+//!
+//! `host_functions!` turns the declaration block at the bottom of this file into the
+//! [`HostFunctions`] trait a host implements and the [`HostFunctionSpec`] table a
+//! wasm engine registers from.
+//!
+//! The split: hand-written here is the vocabulary the declarations are written in —
+//! [`HostError`], [`HostResult`], [`HASH_LEN`] — and everything derived from the
+//! declarations is generated. The expansion names nothing this file does not, so the
+//! two sides meet only in the block below.
+
+#![no_std]
+
+// Not re-exported: the ABI is declared once, here, and this is the only call site.
+use xrpl_host_functions_macros::host_functions;
+
+/// Declares [`HostError`] from one list: the variants, [`HostError::ALL`] and
+/// [`HostError::from_code`]'s table all expand from the codes below.
+///
+/// One list is what makes `ALL` complete. Rust cannot enumerate an enum's
+/// variants — an exhaustive `match` forces an arm per variant but gives nothing to
+/// iterate — so a hand-written `ALL` beside a hand-written enum could only be kept
+/// in step by review, and `ALL`'s whole purpose is to be the set a test can trust.
+/// A code added below gains its `ALL` entry and its `from_code` arm by
+/// construction. `HostFunctionSpec::ALL` is complete the same way, from the
+/// `host_functions!` block.
+macro_rules! host_errors {
+    ($($variant:ident = $code:literal,)+) => {
+        /// Error codes a host function may return.
+        ///
+        /// The discriminants mirror `HostFunctionError` in
+        /// `include/xrpl/tx/wasm/WasmCommon.h`, so a negative `i32` crossing the wasm
+        /// boundary means the same thing to the guest, the Rust host, and the existing
+        /// C++ code. The full set is kept (not just the ones the PoC uses today) to
+        /// preserve that shared meaning.
+        #[derive(Debug, Clone, Copy, PartialEq, Eq)]
+        #[repr(i32)]
+        pub enum HostError {
+            $($variant = $code,)+
+        }
+
+        impl HostError {
+            /// Every error a host function may return, in code order.
+            ///
+            /// The complete set, and complete by construction: a wasm engine's
+            /// split between the codes it hands the guest and the conditions it
+            /// traps on is a decision per variant, so the test that checks the
+            /// split iterates this and a code added to the ABI cannot slip past it.
+            pub const ALL: &'static [HostError] = &[$(HostError::$variant,)+];
+
+            /// The negative wire value the guest sees as the function's return code.
+            #[inline]
+            pub const fn code(self) -> i32 {
+                self as i32
+            }
+
+            /// Reconstruct a `HostError` from its wire code; unknown/positive values
+            /// map to `Internal`.
+            pub const fn from_code(code: i32) -> HostError {
+                match code {
+                    $($code => HostError::$variant,)+
+                    _ => HostError::Internal,
+                }
+            }
+        }
+    };
+}
+
+host_errors! {
+    Internal = -1,
+    FieldNotFound = -2,
+    BufferTooSmall = -3,
+    NoArray = -4,
+    NotLeafField = -5,
+    LocatorMalformed = -6,
+    SlotOutRange = -7,
+    SlotsFull = -8,
+    EmptySlot = -9,
+    LedgerObjNotFound = -10,
+    Decoding = -11,
+    DataFieldTooLarge = -12,
+    PointerOutOfBounds = -13,
+    NoMemExported = -14,
+    InvalidParams = -15,
+    InvalidAccount = -16,
+    InvalidField = -17,
+    IndexOutOfBounds = -18,
+    FloatInputMalformed = -19,
+    FloatComputationError = -20,
+    NoRuntime = -21,
+    OutOfGas = -22,
+    OutOfTransferLimit = -23,
+}
+
+/// Convenience alias for the trait's fallible returns.
+pub type HostResult<T> = Result<T, HostError>;
+
+/// A `sha512Half` digest: the first 32 bytes of a SHA-512, as XRPL uses it.
+pub const HASH_LEN: usize = 32;
+
+/// Declares [`TraceDataType`] from one list, so [`TraceDataType::ALL`],
+/// [`TraceDataType::code`] and [`TraceDataType::from_code`] cannot fall behind the
+/// variants — the reason `host_errors!` above is written this way.
+macro_rules! trace_data_types {
+    ($($(#[$doc:meta])* $variant:ident = $code:literal,)+) => {
+        /// How [`HostFunctions::trace`] is to read its data buffer.
+        ///
+        /// The discriminants are wire values shared with the guest stdlib: append only,
+        /// never renumber. They start at 1, so a zeroed argument names no type rather
+        /// than the first one.
+        ///
+        /// This is the declaration a guest and a host both compile against. The host
+        /// side needs a second one — `cxx` cannot be a dependency here, since this
+        /// crate also links into the guest — so `xrpl-wasm-vm-ffi` declares a shared
+        /// enum for C++ and converts, exhaustively, from this.
+        #[derive(Debug, Clone, Copy, PartialEq, Eq)]
+        #[repr(i32)]
+        pub enum TraceDataType {
+            $($(#[$doc])* $variant = $code,)+
+        }
+
+        impl TraceDataType {
+            /// Every data type a guest may name, in code order.
+            pub const ALL: &'static [TraceDataType] = &[$(TraceDataType::$variant,)+];
+
+            /// The wire value a guest passes to name this type.
+            #[inline]
+            pub const fn code(self) -> i32 {
+                self as i32
+            }
+
+            /// The type `code` names, or `None`: the engine drops a call it cannot
+            /// read rather than guessing at a rendering the guest did not ask for.
+            pub const fn from_code(code: i32) -> Option<TraceDataType> {
+                match code {
+                    $($code => Some(TraceDataType::$variant),)+
+                    _ => None,
+                }
+            }
+        }
+    };
+}
+
+trace_data_types! {
+    /// 8 little-endian bytes, rendered as a signed decimal.
+    Int64 = 1,
+    /// 8 little-endian bytes, rendered as an unsigned decimal.
+    Uint64 = 2,
+    /// A serialized XRPL float: 12 bytes, mantissa then exponent.
+    Xfloat = 3,
+    /// A 20-byte account ID, rendered as base58.
+    Account = 4,
+    /// A serialized `STAmount`.
+    Amount = 5,
+    /// Raw bytes, hex-encoded.
+    AsHex = 6,
+    /// Bytes rendered verbatim as text.
+    AsText = 7,
+}
+
+host_functions! {
+    /// The sequence number of the ledger being built, as 4 little-endian bytes.
+    #[gas = 60]
+    #[wasm_name = "ldgr_index"]
+    fn get_ledger_sqn(&self, out: &mut [u8]) -> HostResult<usize>;
+
+    /// The serialized bytes of one field of the current (escrow) ledger object.
+    #[gas = 70]
+    #[wasm_name = "home_le_field"]
+    fn get_current_ledger_obj_field(&self, field: i32, out: &mut [u8]) -> HostResult<usize>;
+
+    /// The XRPL `sha512Half` of `data`: the first [`HASH_LEN`] bytes of its SHA-512.
+    #[gas = 2000]
+    #[wasm_name = "sha512_half"]
+    fn sha512_half(&self, data: &[u8], out: &mut [u8]) -> HostResult<usize>;
+
+    /// Writes `msg` to the trace log, followed by `data` rendered as `data_type` says.
+    ///
+    /// The one declaration whose wasm function has **no result**: this node's own log
+    /// is its only effect, so a guest is told nothing. An `Err` from a host therefore
+    /// reaches it in no form, and only the host-fatal ones do anything at all.
+    ///
+    /// It is also the one declaration that is **not** the wasm parameter order.
+    /// `data_type` is the third wasm parameter, between the two regions, because that
+    /// is where xrpld's `trace_proto` and the guest stdlib put it; `register.rs` takes
+    /// the arguments in wasm order and calls this in declaration order.
+    #[gas = 30]
+    #[wasm_name = "trace"]
+    fn trace(&self, msg: &str, data: &[u8], data_type: TraceDataType) -> HostResult<()>;
+}
diff --git a/crates/xrpl-host-functions/tests/expansion_hygiene.rs b/crates/xrpl-host-functions/tests/expansion_hygiene.rs
new file mode 100644
index 00000000000..32854bfd72d
--- /dev/null
+++ b/crates/xrpl-host-functions/tests/expansion_hygiene.rs
@@ -0,0 +1,34 @@
+//! `host_functions!` must work outside the crate that declares the ABI: the only
+//! names its expansion needs are the ones the declarations themselves spell.
+
+use xrpl_host_functions::HostResult;
+use xrpl_host_functions_macros::host_functions;
+
+host_functions! {
+    /// Answers with the number it was given.
+    #[gas = 7]
+    #[wasm_name = "ping"]
+    fn ping(&self, number: i32) -> HostResult<i32>;
+}
+
+struct Host;
+
+impl HostFunctions for Host {
+    fn ping(&self, number: i32) -> HostResult<i32> {
+        Ok(number)
+    }
+}
+
+#[test]
+fn the_generated_table_stands_on_its_own() {
+    assert_eq!(HostFunctionSpec::ALL.len(), 1);
+    assert_eq!(HostFunctionSpec::Ping.wasm_name(), "ping");
+    assert_eq!(HostFunctionSpec::Ping.gas(), 7);
+}
+
+/// The generated trait is implementable from another crate, which is the point of
+/// declaring the ABI in a library at all.
+#[test]
+fn the_generated_trait_is_implementable_here() {
+    assert_eq!(Host.ping(3), Ok(3));
+}
diff --git a/crates/xrpl-host-functions/tests/generated_abi.rs b/crates/xrpl-host-functions/tests/generated_abi.rs
new file mode 100644
index 00000000000..c0327f86c75
--- /dev/null
+++ b/crates/xrpl-host-functions/tests/generated_abi.rs
@@ -0,0 +1,190 @@
+//! Exercises what `host_functions!` generates: the trait is implementable and
+//! the spec table agrees with the declarations in `src/lib.rs`.
+
+use std::cell::RefCell;
+use std::collections::HashSet;
+
+use xrpl_host_functions::{
+    HASH_LEN, HostError, HostFunctionSpec, HostFunctions, HostResult, TraceDataType,
+};
+
+/// Records what it was asked to do; enough to prove the trait is usable.
+///
+/// Every method takes `&self`, so a host that records anything keeps it behind
+/// interior mutability.
+#[derive(Default)]
+struct FakeHost {
+    traced: RefCell<Vec<String>>,
+}
+
+/// The contract every byte-producing host function follows: write only if the
+/// value fits, and report its true length either way, so the engine can turn a
+/// value that doesn't fit into `BufferTooSmall` without the host knowing the
+/// guest's buffer size.
+fn put(out: &mut [u8], value: &[u8]) -> HostResult<usize> {
+    if let Some(dst) = out.get_mut(..value.len()) {
+        dst.copy_from_slice(value);
+    }
+    Ok(value.len())
+}
+
+impl HostFunctions for FakeHost {
+    fn get_ledger_sqn(&self, out: &mut [u8]) -> HostResult<usize> {
+        put(out, &7u32.to_le_bytes())
+    }
+
+    /// Fails on a field it doesn't know, so the error channel is exercised too.
+    fn get_current_ledger_obj_field(&self, field: i32, out: &mut [u8]) -> HostResult<usize> {
+        if field < 0 {
+            return Err(HostError::FieldNotFound);
+        }
+        put(out, &[field as u8])
+    }
+
+    fn sha512_half(&self, data: &[u8], out: &mut [u8]) -> HostResult<usize> {
+        let mut digest = [0; HASH_LEN];
+        digest[0] = data.len() as u8;
+        put(out, &digest)
+    }
+
+    fn trace(&self, msg: &str, data: &[u8], data_type: TraceDataType) -> HostResult<()> {
+        self.traced
+            .borrow_mut()
+            .push(format!("{msg}/{data_type:?}/{}", data.len()));
+        Ok(())
+    }
+}
+
+#[test]
+fn the_trait_is_implementable() {
+    let host = FakeHost::default();
+    let mut out = [0u8; HASH_LEN];
+
+    assert_eq!(host.get_ledger_sqn(&mut out), Ok(4));
+    assert_eq!(out[..4], [7, 0, 0, 0]);
+    assert_eq!(host.get_current_ledger_obj_field(3, &mut out), Ok(1));
+    assert_eq!(out[0], 3);
+    assert_eq!(host.sha512_half(b"abc", &mut out), Ok(HASH_LEN));
+    assert_eq!(out[0], 3);
+    assert_eq!(host.trace("hello", b"xy", TraceDataType::AsHex), Ok(()));
+
+    assert_eq!(*host.traced.borrow(), ["hello/AsHex/2"]);
+}
+
+/// The error channel every declaration carries: an `Err` the VM turns into the
+/// wire's negative return code.
+#[test]
+fn a_failing_call_reports_its_error_code() {
+    let host = FakeHost::default();
+    let mut out = [0u8; 8];
+
+    assert_eq!(
+        host.get_current_ledger_obj_field(-1, &mut out),
+        Err(HostError::FieldNotFound)
+    );
+    assert_eq!(HostError::FieldNotFound.code(), -2);
+}
+
+/// A host reports the value's true length even when it cannot write it, which is
+/// what lets the engine answer `BufferTooSmall` on the guest's behalf.
+#[test]
+fn a_short_buffer_still_reports_the_true_length() {
+    let host = FakeHost::default();
+    let mut out = [0u8; 2];
+
+    assert_eq!(host.get_ledger_sqn(&mut out), Ok(4));
+    assert_eq!(
+        out,
+        [0, 0],
+        "nothing is written when the value does not fit"
+    );
+}
+
+/// The VM reaches the host as one shared trait object held in the wasmi `Store`,
+/// which is what the `&self` receivers are for.
+#[test]
+fn the_trait_is_callable_through_a_shared_trait_object() {
+    let fake = FakeHost::default();
+    let host: &dyn HostFunctions = &fake;
+    let mut out = [0u8; 4];
+
+    assert_eq!(host.get_ledger_sqn(&mut out), Ok(4));
+    assert_eq!(
+        host.trace("count", &1i64.to_le_bytes(), TraceDataType::Int64),
+        Ok(())
+    );
+
+    assert_eq!(*fake.traced.borrow(), ["count/Int64/8"]);
+}
+
+/// The whole table, written out: the one place the ABI's wire names and gas costs
+/// appear as literals, and a deliberate change-detector, since both are consensus
+/// input. Everything else reads `HostFunctionSpec::gas()` instead.
+///
+/// `ALL` is in declaration order, so comparing the whole vec pins the order and the
+/// membership too.
+#[test]
+fn the_spec_table_matches_the_declarations() {
+    let table: Vec<(&str, u64)> = HostFunctionSpec::ALL
+        .iter()
+        .map(|function| (function.wasm_name(), function.gas()))
+        .collect();
+
+    assert_eq!(
+        table,
+        [
+            ("ldgr_index", 60),
+            ("home_le_field", 70),
+            ("sha512_half", 2000),
+            ("trace", 30),
+        ]
+    );
+}
+
+/// The other half of the wire vocabulary, and the same change-detector argument: the
+/// codes are what a guest passes, so they are pinned as literals here. `ALL` is in code
+/// order, so the round trip pins the discriminants and not just the membership.
+#[test]
+fn every_trace_data_type_survives_the_wire() {
+    let codes: Vec<i32> = TraceDataType::ALL.iter().map(|t| t.code()).collect();
+
+    assert_eq!(codes, [1, 2, 3, 4, 5, 6, 7]);
+    for &data_type in TraceDataType::ALL {
+        assert_eq!(TraceDataType::from_code(data_type.code()), Some(data_type));
+    }
+}
+
+/// A code no declaration names is refused rather than read as a neighbouring type.
+/// Zero is the one worth naming: it is what a guest sends by omission.
+#[test]
+fn an_unnamed_trace_data_type_code_is_refused() {
+    for code in [0, -1, 8, i32::MAX, i32::MIN] {
+        assert_eq!(TraceDataType::from_code(code), None, "code {code}");
+    }
+}
+
+/// `ALL` is what a wasm engine iterates to register imports, so no two declarations
+/// may collapse to the same wire name. The table above pins membership and order;
+/// this adds only uniqueness, and restates nothing.
+#[test]
+fn every_variant_appears_in_all_exactly_once() {
+    let names: HashSet<&str> = HostFunctionSpec::ALL
+        .iter()
+        .map(|function| function.wasm_name())
+        .collect();
+
+    assert_eq!(names.len(), HostFunctionSpec::ALL.len());
+}
+
+/// Both accessors are `const`, so an engine can build its import and gas tables at
+/// compile time rather than on every invocation. The assertions sit in `const`
+/// blocks so they are checked while compiling, which is the claim; the values
+/// themselves are pinned above.
+#[test]
+fn the_table_is_usable_in_const_context() {
+    const NAME: &str = HostFunctionSpec::Trace.wasm_name();
+    const GAS: u64 = HostFunctionSpec::Trace.gas();
+
+    const { assert!(!NAME.is_empty()) };
+    const { assert!(GAS > 0) };
+}
diff --git a/crates/xrpl-host-functions/tests/host_errors.rs b/crates/xrpl-host-functions/tests/host_errors.rs
new file mode 100644
index 00000000000..7815f5c1a6f
--- /dev/null
+++ b/crates/xrpl-host-functions/tests/host_errors.rs
@@ -0,0 +1,70 @@
+//! Exercises what `host_errors!` generates: the wire codes, the set
+//! [`HostError::ALL`] names, and the round trip between them.
+//!
+//! The codes are consensus input — they are what a guest reads off a failed host
+//! call — so they are pinned here as literals and derived everywhere else.
+
+use xrpl_host_functions::HostError;
+
+/// The whole set, written out in the order `ALL` gives it: the one place the wire
+/// codes appear as literals, and a deliberate change-detector, since a code that
+/// moves changes what every deployed guest is told.
+#[test]
+fn the_error_table_matches_the_declarations() {
+    let table: Vec<(HostError, i32)> = HostError::ALL
+        .iter()
+        .map(|&error| (error, error.code()))
+        .collect();
+
+    assert_eq!(
+        table,
+        [
+            (HostError::Internal, -1),
+            (HostError::FieldNotFound, -2),
+            (HostError::BufferTooSmall, -3),
+            (HostError::NoArray, -4),
+            (HostError::NotLeafField, -5),
+            (HostError::LocatorMalformed, -6),
+            (HostError::SlotOutRange, -7),
+            (HostError::SlotsFull, -8),
+            (HostError::EmptySlot, -9),
+            (HostError::LedgerObjNotFound, -10),
+            (HostError::Decoding, -11),
+            (HostError::DataFieldTooLarge, -12),
+            (HostError::PointerOutOfBounds, -13),
+            (HostError::NoMemExported, -14),
+            (HostError::InvalidParams, -15),
+            (HostError::InvalidAccount, -16),
+            (HostError::InvalidField, -17),
+            (HostError::IndexOutOfBounds, -18),
+            (HostError::FloatInputMalformed, -19),
+            (HostError::FloatComputationError, -20),
+            (HostError::NoRuntime, -21),
+            (HostError::OutOfGas, -22),
+            (HostError::OutOfTransferLimit, -23),
+        ]
+    );
+}
+
+/// Every code a guest can be handed comes back as the error that produced it, so a
+/// caller reading a negative return value recovers the condition and not a
+/// neighbouring one. The table above pins the numbers; this adds only the round
+/// trip.
+#[test]
+fn every_wire_code_round_trips_back_to_its_error() {
+    for &error in HostError::ALL {
+        assert_eq!(HostError::from_code(error.code()), error, "{error:?}");
+    }
+}
+
+/// A code from outside the set is `Internal`: a host that answers something this
+/// ABI does not define has failed in a way the caller cannot act on, and success is
+/// not an error at all.
+#[test]
+fn a_code_outside_the_set_is_internal() {
+    let unassigned = -(HostError::ALL.len() as i32) - 1;
+
+    for code in [unassigned, i32::MIN, 0, 1, i32::MAX] {
+        assert_eq!(HostError::from_code(code), HostError::Internal, "{code}");
+    }
+}
diff --git a/crates/xrpl-wasm-testkit/Cargo.toml b/crates/xrpl-wasm-testkit/Cargo.toml
new file mode 100644
index 00000000000..06c1e7c3663
--- /dev/null
+++ b/crates/xrpl-wasm-testkit/Cargo.toml
@@ -0,0 +1,11 @@
+[package]
+name = "xrpl-wasm-testkit"
+version = "0.1.0"
+edition.workspace = true
+
+[lib]
+crate-type = ["staticlib", "rlib"]
+
+[dependencies]
+cxx.workspace = true
+wat = "1"
diff --git a/crates/xrpl-wasm-testkit/src/lib.rs b/crates/xrpl-wasm-testkit/src/lib.rs
new file mode 100644
index 00000000000..58d3db1885b
--- /dev/null
+++ b/crates/xrpl-wasm-testkit/src/lib.rs
@@ -0,0 +1,49 @@
+//! Assembles WebAssembly text for the C++ test suite. **Test-only.**
+//!
+//! A crate of its own rather than an entry on `xrpl-wasm-vm-ffi`, and the separation is the
+//! point. The engine pins `wasmi = { default-features = false }` precisely so a text
+//! assembler cannot reach the consensus path — wasmi's `wat` feature is on by default and
+//! makes `Module::new` accept text as readily as binary, which would make a transaction's
+//! validity a build flag (review finding A5). Putting `compile_wat` on the production bridge
+//! would link `wat` into xrpld even if nothing called it.
+//!
+//! Linked only into `xrpl_tests`, never into `libxrpl` or `xrpld`, so "no assembler in the
+//! shipped node" is a property of the link graph rather than a flag someone can flip.
+#![deny(rustdoc::broken_intra_doc_links)]
+
+#[cxx::bridge(namespace = "rs::wasm_testkit")]
+mod ffi {
+    extern "Rust" {
+        /// Assemble `wat` to a wasm module.
+        ///
+        /// Throws `rust::Error` on invalid input, which is what a test wants: a typo in a
+        /// fixture should fail the test that holds it, at the line that holds it.
+        fn compile_wat(wat: &str) -> Result<Vec<u8>>;
+    }
+}
+
+fn compile_wat(wat: &str) -> Result<Vec<u8>, wat::Error> {
+    wat::parse_str(wat)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::compile_wat;
+
+    #[test]
+    fn a_module_assembles_to_something_beginning_with_the_wasm_magic() {
+        let wasm = compile_wat("(module)").expect("assembles");
+
+        assert_eq!(&wasm[..4], b"\0asm");
+    }
+
+    #[test]
+    fn a_typo_is_an_error_rather_than_a_module() {
+        let error = compile_wat("(module (func (export").expect_err("must not assemble");
+
+        assert!(
+            !error.to_string().is_empty(),
+            "the error has to say something"
+        );
+    }
+}
diff --git a/crates/xrpl-wasm-vm-ffi/Cargo.toml b/crates/xrpl-wasm-vm-ffi/Cargo.toml
new file mode 100644
index 00000000000..c301eb707ae
--- /dev/null
+++ b/crates/xrpl-wasm-vm-ffi/Cargo.toml
@@ -0,0 +1,12 @@
+[package]
+name = "xrpl-wasm-vm-ffi"
+version = "0.1.0"
+edition.workspace = true
+
+[lib]
+crate-type = ["staticlib", "rlib"]
+
+[dependencies]
+cxx.workspace = true
+xrpl-host-functions = { path = "../xrpl-host-functions" }
+xrpl-wasm-vm = { path = "../xrpl-wasm-vm" }
diff --git a/crates/xrpl-wasm-vm-ffi/src/lib.rs b/crates/xrpl-wasm-vm-ffi/src/lib.rs
new file mode 100644
index 00000000000..5c9b4e9a8c6
--- /dev/null
+++ b/crates/xrpl-wasm-vm-ffi/src/lib.rs
@@ -0,0 +1,656 @@
+//! The cxx bridge between the escrow wasm engine and xrpld.
+//!
+//! Three crossings. C++ calls `run_escrow` once per escrow finish; the engine's host
+//! calls come back out through the C++ `HostContext`, which `CxxHost` presents to the
+//! engine as an ordinary [`HostFunctions`] implementor. The ABI those calls speak is
+//! declared once, in `xrpl-host-functions`, so neither side of this file gets to
+//! restate a signature.
+//!
+//! `check_escrow` is the third, and it crosses in one direction only: screening a
+//! module needs no host, so nothing comes back out.
+//!
+//! **Neither direction may unwind into the other**, and the two halves of that are
+//! not symmetric:
+//!
+//! - A **Rust panic** is caught here, by `guarded`. Letting one reach C++ is
+//!   undefined behaviour; `[profile.release]` turns overflow checks on, so this is a
+//!   live path and not a formality.
+//! - A **C++ exception** is stopped on the C++ side: every `HostContext` method is
+//!   `noexcept` and reports failure as a negative `HostError` code. That is what
+//!   makes `guarded` sufficient — see its documentation.
+//!
+//! Everything hand-written here is private, so the names above are code spans rather
+//! than links, and `cargo doc` needs `--document-private-items` to show any of it.
+//! That is also why this crate, unlike `xrpl-wasm-vm`, does not
+//! `deny(unreachable_pub)`: cxx's expansion is `pub` throughout by necessity, leaving
+//! the lint nothing but generated code to fire on.
+#![deny(rustdoc::broken_intra_doc_links)]
+
+use std::any::Any;
+use std::panic::{AssertUnwindSafe, catch_unwind};
+use xrpl_host_functions::{HostError, HostFunctions, HostResult, TraceDataType};
+use xrpl_wasm_vm::{CheckError, RunError, RunFailure, RunOutcome, check, run};
+
+/// [`guarded`] must be able to stop an unwind. Under `panic = "abort"` it cannot,
+/// and every arithmetic overflow in the engine becomes a node crash instead of a
+/// `tecINTERNAL`.
+#[cfg(panic = "abort")]
+compile_error!(
+    "xrpl-wasm-vm-ffi requires panic=unwind: run_escrow catches panics rather than \
+     letting them cross into C++"
+);
+
+#[cxx::bridge(namespace = "rs::wasm_vm")]
+mod ffi {
+    /// Which outcome a run had — one variant per way [`run`] can end, so the caller
+    /// maps a status to a TER rather than reading a message.
+    #[derive(Debug, Hash)]
+    #[repr(i32)]
+    enum RunStatus {
+        /// The entry point returned.
+        Ok,
+        /// `wasm` is not a valid module under this engine's configuration.
+        Compile,
+        /// The module would not instantiate.
+        Instantiate,
+        /// No export of that name with signature `() -> i32`.
+        EntryPoint,
+        /// Gas exhausted, by the guest's instructions or a host call's charge.
+        OutOfGas,
+        /// The host could not serve a call, including any exception it caught.
+        Internal,
+        /// A host call had no linear memory to work in.
+        NoMemory,
+        /// The guest trapped.
+        Trap,
+        /// The engine panicked. A defect in this crate or the one below it.
+        Panic,
+    }
+
+    /// A run's outcome, flattened: cxx enums carry no payload, so the status, the
+    /// cost and the description travel side by side.
+    struct RunResult {
+        status: RunStatus,
+        /// What the entry point returned. Meaningful only when `status` is `Ok`.
+        result: i32,
+        /// Gas consumed. The whole limit when gas ran out; `0` when the module never
+        /// ran, or when the cost could not be trusted (`Internal`, `Panic`).
+        gas_used: u64,
+        /// The engine's own description of the outcome, for the log. Empty on `Ok`.
+        detail: String,
+    }
+
+    /// Why a module cannot be run — one variant per way [`check`] can refuse it,
+    /// so the caller maps a status to a TER rather than reading a message.
+    #[derive(Debug, Hash)]
+    #[repr(i32)]
+    enum CheckStatus {
+        /// The module compiles, imports only what the engine serves, and exports
+        /// the entry point as `() -> i32`.
+        Ok,
+        /// `wasm` is not a valid module under this engine's configuration.
+        Compile,
+        /// An import the engine does not define: another module namespace, a name
+        /// that is not a host function, or one imported as something else.
+        Import,
+        /// No export of that name with signature `() -> i32`.
+        EntryPoint,
+        /// The module asks for more linear memory than the engine grants.
+        Memory,
+        /// The engine panicked. A defect in this crate or the one below it, and
+        /// not a fault in the module — which is why it is a status of its own
+        /// rather than one more way a contract can be malformed.
+        Panic,
+    }
+
+    /// A check's verdict. No cost, because nothing was executed.
+    struct CheckResult {
+        status: CheckStatus,
+        /// The engine's own description of the refusal, for the log. Empty on
+        /// `Ok`.
+        detail: String,
+    }
+
+    /// How `HostContext::trace` is to read its data buffer.
+    ///
+    /// **Declared here so that C++ does not declare it.** A shared enum is emitted into
+    /// the generated header as `xrpl::TraceDataType`, which is the definition
+    /// `HostContext.cpp` switches on — so the variants and their wire values are
+    /// written once, in Rust, for both languages.
+    ///
+    /// It is not the same type as [`xrpl_host_functions::TraceDataType`], and cannot
+    /// be: the ABI crate is `no_std` with no dependencies so that it also links into
+    /// the guest, and `cxx` is neither. [`crossed`] converts, in a `match` that is
+    /// exhaustive over the ABI's enum — so a data type added there fails to compile
+    /// until it is added here, which is the drift check the hand-written C++ copy
+    /// never had.
+    #[namespace = "xrpl"]
+    #[derive(Debug, Hash)]
+    #[repr(i32)]
+    enum TraceDataType {
+        Int64 = 1,
+        Uint64 = 2,
+        Xfloat = 3,
+        Account = 4,
+        Amount = 5,
+        AsHex = 6,
+        AsText = 7,
+    }
+
+    extern "Rust" {
+        /// Run `wasm`'s `function_name` export with `gas` fuel, servicing host calls
+        /// through `host`.
+        ///
+        /// Reports every outcome as a [`RunStatus`] and **never throws**: an
+        /// exception is a poor interface for a condition the caller has to turn into
+        /// a TER anyway, and a panic reaching C++ would be undefined behaviour.
+        ///
+        /// `gas` is the run's whole budget. `0` is a run that cannot execute an
+        /// instruction; the C++ front refuses it as `temBAD_AMOUNT` before calling
+        /// here, so it is not given a status of its own.
+        fn run_escrow(host: &HostContext, wasm: &[u8], gas: u64, function_name: &str) -> RunResult;
+
+        /// Screen `wasm` before it can reach the ledger: whether [`run_escrow`]
+        /// would refuse it before the guest's first instruction.
+        ///
+        /// Takes no host, no gas and no store — the verdict comes from the
+        /// compiled module alone, which is what makes it callable from a
+        /// transaction's preflight, where there is no ledger to serve a host call
+        /// from. **Never throws**, for the same reason [`run_escrow`] does not.
+        fn check_escrow(wasm: &[u8], function_name: &str) -> CheckResult;
+    }
+
+    unsafe extern "C++" {
+        include!("xrpl/tx/wasm/HostContext.h");
+
+        /// The C++ side of the ABI: one method per host function, forwarding to
+        /// `xrpl::HostFunctions`.
+        ///
+        /// Every method is `noexcept` and answers with a code, so a host call cannot
+        /// unwind into the engine.
+        ///
+        /// `cxx_name` on each method below is not cosmetic: the declarations keep the
+        /// ABI's names here and rippled's camelBack over there, so neither side has
+        /// to spell the other's convention.
+        #[namespace = "xrpl"]
+        type HostContext;
+
+        /// A byte-producing call is handed `out` and returns the value's **true
+        /// length**, writing it only if the whole value fits. Returning a length past
+        /// `out` is how a guest learns the size to ask for; the engine turns it into
+        /// `BufferTooSmall`, so C++ never needs to know the guest's capacity.
+        ///
+        /// A negative return is a `HostError` code.
+        #[namespace = "xrpl"]
+        #[cxx_name = "getLedgerSqn"]
+        fn get_ledger_sqn(self: &HostContext, out: &mut [u8]) -> i32;
+
+        #[namespace = "xrpl"]
+        #[cxx_name = "getCurrentLedgerObjField"]
+        fn get_current_ledger_obj_field(self: &HostContext, field: i32, out: &mut [u8]) -> i32;
+
+        #[namespace = "xrpl"]
+        #[cxx_name = "sha512Half"]
+        fn sha512_half(self: &HostContext, data: &[u8], out: &mut [u8]) -> i32;
+
+        /// Renders `data` as `data_type` says and writes it to this node's log with
+        /// `msg`. Answers nothing at all: the guest's wasm function has no result, and
+        /// C++ swallows a malformed buffer rather than reporting it, so there is no
+        /// failure for this side to encode.
+        ///
+        /// The engine has already refused a code that names no type, so what crosses
+        /// here is always one of the variants.
+        #[namespace = "xrpl"]
+        fn trace(self: &HostContext, msg: &str, data: &[u8], data_type: TraceDataType);
+    }
+}
+
+/// Sized carrier for the [`HostFunctions`] implementation.
+///
+/// [`ffi::HostContext`] is an opaque C++ type and therefore `!Sized`, so it cannot
+/// be coerced to `&dyn HostFunctions` itself.
+struct CxxHost<'a> {
+    ctx: &'a ffi::HostContext,
+}
+
+/// A byte-producing call's answer: the value's true length, or its error code.
+///
+/// The conversion *is* the sign test — it fails on exactly the negative values — so
+/// there is no cast to argue about.
+///
+/// A named function rather than a `From` impl, and not by preference: every type
+/// involved — `i32`, `Result`, `HostError` — is foreign to this crate, so the orphan
+/// rule forbids the impl.
+fn bytes_written(n: i32) -> HostResult<usize> {
+    usize::try_from(n).map_err(|_| HostError::from_code(n))
+}
+
+/// The ABI's data type as the shared enum C++ was given a definition of.
+///
+/// A `match` rather than a cast through `code()`: the cast would compile for a variant
+/// nobody added to [`ffi::TraceDataType`] and hand C++ a value its `switch` does not
+/// name. This is the whole reason the two lists cannot drift.
+fn crossed(data_type: TraceDataType) -> ffi::TraceDataType {
+    match data_type {
+        TraceDataType::Int64 => ffi::TraceDataType::Int64,
+        TraceDataType::Uint64 => ffi::TraceDataType::Uint64,
+        TraceDataType::Xfloat => ffi::TraceDataType::Xfloat,
+        TraceDataType::Account => ffi::TraceDataType::Account,
+        TraceDataType::Amount => ffi::TraceDataType::Amount,
+        TraceDataType::AsHex => ffi::TraceDataType::AsHex,
+        TraceDataType::AsText => ffi::TraceDataType::AsText,
+    }
+}
+
+impl HostFunctions for CxxHost<'_> {
+    fn get_ledger_sqn(&self, out: &mut [u8]) -> HostResult<usize> {
+        bytes_written(self.ctx.get_ledger_sqn(out))
+    }
+
+    fn get_current_ledger_obj_field(&self, field: i32, out: &mut [u8]) -> HostResult<usize> {
+        bytes_written(self.ctx.get_current_ledger_obj_field(field, out))
+    }
+
+    fn sha512_half(&self, data: &[u8], out: &mut [u8]) -> HostResult<usize> {
+        bytes_written(self.ctx.sha512_half(data, out))
+    }
+
+    fn trace(&self, msg: &str, data: &[u8], data_type: TraceDataType) -> HostResult<()> {
+        self.ctx.trace(msg, data, crossed(data_type));
+        Ok(())
+    }
+}
+
+fn run_escrow(
+    host: &ffi::HostContext,
+    wasm: &[u8],
+    gas: u64,
+    function_name: &str,
+) -> ffi::RunResult {
+    guarded(
+        || {
+            let host = CxxHost { ctx: host };
+            run(wasm, gas, &host, function_name).into()
+        },
+        ffi::RunResult::panicked,
+    )
+}
+
+fn check_escrow(wasm: &[u8], function_name: &str) -> ffi::CheckResult {
+    guarded(
+        || check(wasm, function_name).into(),
+        ffi::CheckResult::panicked,
+    )
+}
+
+impl ffi::RunResult {
+    /// A run the engine panicked in.
+    ///
+    /// The cost is not reported: a panicking run's meter is not evidence of
+    /// anything, and `0` says "unknown" where a number would say "this is what it
+    /// owed".
+    fn panicked(detail: String) -> ffi::RunResult {
+        ffi::RunResult {
+            status: ffi::RunStatus::Panic,
+            result: 0,
+            gas_used: 0,
+            detail,
+        }
+    }
+}
+
+impl ffi::CheckResult {
+    /// A check the engine panicked in.
+    fn panicked(detail: String) -> ffi::CheckResult {
+        ffi::CheckResult {
+            status: ffi::CheckStatus::Panic,
+            detail,
+        }
+    }
+}
+
+/// Run `body`, handing a panic to `panicked` rather than letting it unwind into
+/// C++.
+///
+/// **Why catching here is enough.** An unwind can only be caught where every frame
+/// between the panic and the catch is Rust, and every frame here is: the engine and
+/// wasmi are Rust, and a host call cannot start a C++ unwind because each
+/// `HostContext` method is `noexcept` and answers with a code. So the only unwind
+/// that can reach this frame started in Rust, and this stops it.
+///
+/// [`AssertUnwindSafe`] is sound because nothing survives to be observed in a torn
+/// state: the store, the linker and the host wrapper are all dropped on the way out,
+/// and the one thing that outlives the call — the C++ `HostContext` — is only ever
+/// touched through those `noexcept` methods, which either complete or report.
+///
+/// Generic over the result so both crossings share the one catch: the two answer
+/// with different structs, and a second `catch_unwind` is the last thing this file
+/// should have two of.
+fn guarded<T>(body: impl FnOnce() -> T, panicked: impl FnOnce(String) -> T) -> T {
+    catch_unwind(AssertUnwindSafe(body)).unwrap_or_else(|payload| panicked(panic_detail(&*payload)))
+}
+
+/// The panic's message, for the log.
+///
+/// A `panic!` payload is a `&str` or a `String`; anything else is a `panic_any` that
+/// nothing below this crate makes, and it still has to produce a line.
+fn panic_detail(payload: &(dyn Any + Send)) -> String {
+    let message = payload
+        .downcast_ref::<&str>()
+        .copied()
+        .or_else(|| payload.downcast_ref::<String>().map(String::as_str))
+        .unwrap_or("payload is not a string");
+    format!("panicked: {message}")
+}
+
+/// The engine's two-channel result on the one struct cxx can carry.
+///
+/// A `From` rather than a named function because the mapping is total and there is
+/// only one of it: every field of the wire struct is decided by the outcome, so
+/// there is no second reading for a name to distinguish.
+impl From<Result<RunOutcome, RunFailure>> for ffi::RunResult {
+    fn from(result: Result<RunOutcome, RunFailure>) -> ffi::RunResult {
+        match result {
+            Ok(RunOutcome { result, fuel_used }) => ffi::RunResult {
+                status: ffi::RunStatus::Ok,
+                result,
+                gas_used: fuel_used,
+                detail: String::new(),
+            },
+            // `fuel_used` is carried on both channels by construction, so a failed
+            // run reports its cost here without this having to decide what one is.
+            Err(RunFailure { error, fuel_used }) => ffi::RunResult {
+                status: ffi::RunStatus::from(&error),
+                result: 0,
+                gas_used: fuel_used,
+                detail: error.to_string(),
+            },
+        }
+    }
+}
+
+/// The status a [`RunError`] crosses as.
+///
+/// Exhaustive rather than closed with a wildcard: an outcome added to the engine has
+/// to be given a status — and therefore a TER on the far side — before this compiles.
+impl From<&RunError> for ffi::RunStatus {
+    fn from(error: &RunError) -> ffi::RunStatus {
+        match error {
+            RunError::Compile(_) => ffi::RunStatus::Compile,
+            RunError::Instantiate(_) => ffi::RunStatus::Instantiate,
+            RunError::EntryPoint(_) => ffi::RunStatus::EntryPoint,
+            RunError::OutOfGas => ffi::RunStatus::OutOfGas,
+            RunError::Internal => ffi::RunStatus::Internal,
+            RunError::NoMemory => ffi::RunStatus::NoMemory,
+            RunError::Trap(_) => ffi::RunStatus::Trap,
+        }
+    }
+}
+
+/// A verdict on the wire. No cost to carry, so `Ok` is the empty description.
+impl From<Result<(), CheckError>> for ffi::CheckResult {
+    fn from(result: Result<(), CheckError>) -> ffi::CheckResult {
+        match result {
+            Ok(()) => ffi::CheckResult {
+                status: ffi::CheckStatus::Ok,
+                detail: String::new(),
+            },
+            Err(error) => ffi::CheckResult {
+                status: ffi::CheckStatus::from(&error),
+                detail: error.to_string(),
+            },
+        }
+    }
+}
+
+/// The status a [`CheckError`] crosses as, exhaustive for the same reason
+/// [`ffi::RunStatus`]'s conversion is.
+impl From<&CheckError> for ffi::CheckStatus {
+    fn from(error: &CheckError) -> ffi::CheckStatus {
+        match error {
+            CheckError::Compile(_) => ffi::CheckStatus::Compile,
+            CheckError::Import(_) => ffi::CheckStatus::Import,
+            CheckError::EntryPoint(_) => ffi::CheckStatus::EntryPoint,
+            CheckError::Memory(_) => ffi::CheckStatus::Memory,
+        }
+    }
+}
+
+/// These tests reach none of the `extern "C++"` methods, which is what lets the test
+/// binary link at all: the C++ side of the bridge exists only in the CMake build, so
+/// a test that called one would fail to link rather than fail.
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn ok(result: i32, fuel_used: u64) -> ffi::RunResult {
+        let outcome: Result<RunOutcome, RunFailure> = Ok(RunOutcome { result, fuel_used });
+        outcome.into()
+    }
+
+    fn failed(error: RunError, fuel_used: u64) -> ffi::RunResult {
+        let outcome: Result<RunOutcome, RunFailure> = Err(RunFailure { error, fuel_used });
+        outcome.into()
+    }
+
+    #[test]
+    fn a_completed_run_carries_its_value_and_its_cost() {
+        let crossed = ok(5, 1234);
+
+        assert_eq!(crossed.status, ffi::RunStatus::Ok);
+        assert_eq!(crossed.result, 5);
+        assert_eq!(crossed.gas_used, 1234);
+        assert_eq!(crossed.detail, "", "a completed run has nothing to explain");
+    }
+
+    /// The cost is the point: a contract that burns its gas and traps is charged.
+    #[test]
+    fn a_failed_run_carries_its_cost_and_the_engines_own_words() {
+        let crossed = failed(RunError::Trap("unreachable".to_string()), 900);
+
+        assert_eq!(crossed.status, ffi::RunStatus::Trap);
+        assert_eq!(crossed.gas_used, 900);
+        assert_eq!(crossed.detail, "trap: unreachable");
+        assert_eq!(crossed.result, 0, "a failed run returned no value");
+    }
+
+    /// The `RunError` set as the test *expects* it, not as the conversion reports it:
+    /// deriving it from the code under test would make the assertion vacuous.
+    fn every_run_error() -> Vec<RunError> {
+        vec![
+            RunError::Compile(String::new()),
+            RunError::Instantiate(String::new()),
+            RunError::EntryPoint(String::new()),
+            RunError::OutOfGas,
+            RunError::Internal,
+            RunError::NoMemory,
+            RunError::Trap(String::new()),
+        ]
+    }
+
+    /// Distinct statuses, because the TER map on the far side reads nothing else. Two
+    /// outcomes sharing one status would silently collapse two TERs into one.
+    #[test]
+    fn every_run_error_crosses_as_a_status_of_its_own() {
+        let mut seen = Vec::new();
+        for error in every_run_error() {
+            let status = ffi::RunStatus::from(&error);
+            assert!(
+                !seen.contains(&status),
+                "{error:?} shares {status:?} with an earlier outcome"
+            );
+            seen.push(status);
+        }
+    }
+
+    /// `Ok` is the one status no failure may take: the far side reads it as "the
+    /// contract returned", and would then read `result` off a run that produced none.
+    #[test]
+    fn no_failure_crosses_as_success() {
+        for error in every_run_error() {
+            assert_ne!(
+                ffi::RunStatus::from(&error),
+                ffi::RunStatus::Ok,
+                "{error:?}"
+            );
+        }
+    }
+
+    #[test]
+    fn a_panic_becomes_a_status_instead_of_an_unwind() {
+        let crossed = guarded(|| panic!("the engine came apart"), ffi::RunResult::panicked);
+
+        assert_eq!(crossed.status, ffi::RunStatus::Panic);
+        assert_eq!(crossed.detail, "panicked: the engine came apart");
+        assert_eq!(crossed.gas_used, 0, "a panicking run reports no cost");
+    }
+
+    /// A formatted `panic!` payload is a `String` rather than a `&str`, so both
+    /// downcasts are load-bearing.
+    #[test]
+    fn a_formatted_panic_keeps_its_message() {
+        let overflowed = 3;
+        let crossed = guarded(
+            || panic!("gas underflowed by {overflowed}"),
+            ffi::RunResult::panicked,
+        );
+
+        assert_eq!(crossed.detail, "panicked: gas underflowed by 3");
+    }
+
+    #[test]
+    fn a_panic_with_no_message_still_reports_one() {
+        let crossed = guarded(|| std::panic::panic_any(7u32), ffi::RunResult::panicked);
+
+        assert_eq!(crossed.status, ffi::RunStatus::Panic);
+        assert_eq!(crossed.detail, "panicked: payload is not a string");
+    }
+
+    #[test]
+    fn a_run_that_does_not_panic_is_untouched() {
+        let crossed = guarded(|| ok(1, 2), ffi::RunResult::panicked);
+
+        assert_eq!(crossed.status, ffi::RunStatus::Ok);
+        assert_eq!(crossed.result, 1);
+        assert_eq!(crossed.gas_used, 2);
+    }
+
+    /// [`crossed`] being exhaustive makes the two lists hold the same *variants*;
+    /// this makes them hold the same *numbers*, which is what actually crosses. A
+    /// `match` arm pointed at the wrong variant would pass the compiler and fail
+    /// here.
+    ///
+    /// Over `TraceDataType::ALL`, so it is the whole set rather than a sample: a data
+    /// type added to the ABI arrives already asserted against the shared enum.
+    #[test]
+    fn every_data_type_crosses_as_the_same_wire_value() {
+        for &data_type in TraceDataType::ALL {
+            assert_eq!(
+                crossed(data_type).repr,
+                data_type.code(),
+                "{data_type:?} crosses as a different value than the ABI gives it"
+            );
+        }
+    }
+
+    #[test]
+    fn a_negative_answer_is_an_error_code_and_a_length_is_a_length() {
+        assert_eq!(bytes_written(32), Ok(32));
+        assert_eq!(bytes_written(0), Ok(0));
+        assert_eq!(bytes_written(-3), Err(HostError::BufferTooSmall));
+        assert_eq!(bytes_written(-14), Err(HostError::NoMemExported));
+    }
+
+    /// An exception caught on the C++ side arrives as `-1`, which has to reach the
+    /// engine as a *fatal* error so the run stops and the transaction is
+    /// `tecINTERNAL` — not as a code handed to the contract to interpret.
+    #[test]
+    fn a_caught_cxx_exception_arrives_as_internal() {
+        assert_eq!(bytes_written(-1), Err(HostError::Internal));
+    }
+
+    // -----------------------------------------------------------------------
+    // The check crossing
+    //
+    // `check_escrow` takes no host, so unlike `run_escrow` it can be called
+    // outright here — the modules are hand-written bytes because this crate has
+    // no assembler and needs none for two of them.
+    // -----------------------------------------------------------------------
+
+    /// The smallest valid module: the eight-byte header and nothing else. It
+    /// compiles and imports nothing, so it reaches the entry-point stage.
+    const EMPTY_MODULE: [u8; 8] = [0x00, 0x61, 0x73, 0x6d, 0x01, 0x00, 0x00, 0x00];
+
+    #[test]
+    fn a_module_that_does_not_compile_crosses_as_compile() {
+        let crossed = check_escrow(b"not wasm", "escrow_finish");
+
+        assert_eq!(crossed.status, ffi::CheckStatus::Compile);
+        assert!(
+            crossed.detail.starts_with("compile: "),
+            "{}",
+            crossed.detail
+        );
+    }
+
+    /// The whole crossing, end to end: a real module through the real engine, with
+    /// the refusal the C++ side will log.
+    #[test]
+    fn a_module_without_the_entry_point_crosses_as_entry_point() {
+        let crossed = check_escrow(&EMPTY_MODULE, "escrow_finish");
+
+        assert_eq!(crossed.status, ffi::CheckStatus::EntryPoint);
+        assert_eq!(crossed.detail, "no entry point 'escrow_finish'");
+    }
+
+    /// The `CheckError` set as the test *expects* it, not as the conversion reports
+    /// it: deriving it from the code under test would make the assertion vacuous.
+    fn every_check_error() -> Vec<CheckError> {
+        vec![
+            CheckError::Compile(String::new()),
+            CheckError::Import(String::new()),
+            CheckError::EntryPoint(String::new()),
+            CheckError::Memory(String::new()),
+        ]
+    }
+
+    /// Distinct statuses, because the TER map on the far side reads nothing else.
+    #[test]
+    fn every_check_error_crosses_as_a_status_of_its_own() {
+        let mut seen = Vec::new();
+        for error in every_check_error() {
+            let status = ffi::CheckStatus::from(&error);
+            assert!(
+                !seen.contains(&status),
+                "{error:?} shares {status:?} with an earlier refusal"
+            );
+            seen.push(status);
+        }
+    }
+
+    /// `Ok` is the one status no refusal may take: the far side reads it as
+    /// `tesSUCCESS` and would let the module through.
+    #[test]
+    fn no_refusal_crosses_as_success() {
+        for error in every_check_error() {
+            assert_ne!(
+                ffi::CheckStatus::from(&error),
+                ffi::CheckStatus::Ok,
+                "{error:?}"
+            );
+        }
+    }
+
+    /// A panic during a check is its own status rather than one more malformed
+    /// module: the far side answers a node-local failure, not `temBAD_WASM`.
+    #[test]
+    fn a_panic_during_a_check_becomes_a_status_instead_of_an_unwind() {
+        let crossed = guarded(
+            || panic!("the checker came apart"),
+            ffi::CheckResult::panicked,
+        );
+
+        assert_eq!(crossed.status, ffi::CheckStatus::Panic);
+        assert_eq!(crossed.detail, "panicked: the checker came apart");
+    }
+}
diff --git a/crates/xrpl-wasm-vm/Cargo.toml b/crates/xrpl-wasm-vm/Cargo.toml
new file mode 100644
index 00000000000..21a5a6f6088
--- /dev/null
+++ b/crates/xrpl-wasm-vm/Cargo.toml
@@ -0,0 +1,11 @@
+[package]
+name = "xrpl-wasm-vm"
+version = "0.1.0"
+edition.workspace = true
+
+[dependencies]
+wasmi = { version = "1.1.0", default-features = false, features = ["std"] }
+xrpl-host-functions = { path = "../xrpl-host-functions" }
+
+[dev-dependencies]
+wat = "1"
diff --git a/crates/xrpl-wasm-vm/src/abi.rs b/crates/xrpl-wasm-vm/src/abi.rs
new file mode 100644
index 00000000000..74a46727ec4
--- /dev/null
+++ b/crates/xrpl-wasm-vm/src/abi.rs
@@ -0,0 +1,365 @@
+use crate::region::Region;
+use crate::vm::{MAX_FIELD_BYTES, VmState};
+use wasmi::{Caller, Memory};
+use xrpl_host_functions::{HostError, HostFunctionSpec, HostFunctions, HostResult};
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub(crate) struct FatalHostError(pub(crate) HostError);
+
+impl wasmi::errors::HostError for FatalHostError {}
+
+impl core::fmt::Display for FatalHostError {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        write!(f, "host call refused: {:?}", self.0)
+    }
+}
+
+/// Whether a [`HostError`] stops the run instead of reaching the guest as a code.
+pub(crate) fn is_fatal(error: HostError) -> bool {
+    matches!(
+        error,
+        HostError::OutOfGas | HostError::Internal | HostError::NoMemExported
+    )
+}
+
+/// Charge the call's gas, run its body, put the result on the wire. The one path
+/// every registered closure takes, so gas cannot be forgotten.
+pub(crate) fn charged(
+    caller: &mut Caller<'_, VmState<'_>>,
+    op: HostFunctionSpec,
+    body: impl FnOnce(&mut Caller<'_, VmState<'_>>) -> HostResult<i32>,
+) -> Result<i32, wasmi::Error> {
+    to_wire(charge(caller, op.gas()).and_then(|()| body(caller)))
+}
+
+/// [`charged`] for a call the guest gets no answer from: its wasm function has no
+/// result, so a soft error has nowhere to go and is dropped. The gas is charged first
+/// and charged whatever happens after, so the cost is all such a call leaves behind.
+///
+/// Only `trace` takes this path.
+pub(crate) fn charged_unreported(
+    caller: &mut Caller<'_, VmState<'_>>,
+    op: HostFunctionSpec,
+    body: impl FnOnce(&mut Caller<'_, VmState<'_>>) -> HostResult<()>,
+) -> Result<(), wasmi::Error> {
+    dropped(charge(caller, op.gas()).and_then(|()| body(caller)))
+}
+
+/// [`to_wire`] for a call with no result: there is no return value to encode a soft
+/// error in, so it is dropped. The host-fatal ones still stop the run — those are a
+/// property of the run, not an answer to the call.
+fn dropped(result: HostResult<()>) -> Result<(), wasmi::Error> {
+    match result {
+        Err(error) if is_fatal(error) => Err(wasmi::Error::host(FatalHostError(error))),
+        _ => Ok(()),
+    }
+}
+
+fn to_wire(result: HostResult<i32>) -> Result<i32, wasmi::Error> {
+    match result {
+        Ok(value) => Ok(value),
+        Err(error) if is_fatal(error) => Err(wasmi::Error::host(FatalHostError(error))),
+        Err(error) => Ok(error.code()),
+    }
+}
+
+/// Deduct `cost` fuel; `OutOfGas` if it would go negative.
+fn charge<T>(caller: &mut Caller<'_, T>, cost: u64) -> Result<(), HostError> {
+    let remaining = caller.get_fuel().map_err(|_| HostError::Internal)?;
+    match remaining.checked_sub(cost) {
+        Some(left) => caller.set_fuel(left).map_err(|_| HostError::Internal),
+        None => {
+            let _ = caller.set_fuel(0);
+            Err(HostError::OutOfGas)
+        }
+    }
+}
+
+fn charge_transfer(state: &VmState<'_>, n: usize) -> Result<(), HostError> {
+    let n = n as u64;
+    let remaining = state.transfer_budget.get();
+    match remaining.checked_sub(n) {
+        Some(left) => {
+            state.transfer_budget.set(left);
+            Ok(())
+        }
+        None => Err(HostError::OutOfTransferLimit),
+    }
+}
+
+fn memory(caller: &Caller<'_, VmState<'_>>) -> Result<Memory, HostError> {
+    caller.data().memory.ok_or(HostError::NoMemExported)
+}
+
+/// [`Region::read`] of the guest's memory, for a call that reads and writes nothing
+/// back (`trace`).
+pub(crate) fn read_borrowed<'a>(
+    caller: &'a Caller<'_, VmState<'_>>,
+    input: Region,
+) -> HostResult<&'a [u8]> {
+    let mem = memory(caller)?;
+    input.read(mem.data(caller))
+}
+
+/// Service a call whose answer is bytes, written straight into the guest's output
+/// region.
+///
+/// **`fill` returns the value's true length, not what it wrote**: a host holding 64
+/// bytes and offered room for 4 writes nothing and answers `64`, which is how the
+/// guest learns the size to ask for. So `n` is bounded by neither the region nor the
+/// cap, and both checks below are reachable.
+pub(crate) fn write_into(
+    caller: &mut Caller<'_, VmState<'_>>,
+    out: Region,
+    fill: impl FnOnce(&dyn HostFunctions, &mut [u8]) -> HostResult<usize>,
+) -> HostResult<i32> {
+    let range = out.range()?;
+    let cap = range.len();
+    let mem = memory(caller)?;
+    let host: &dyn HostFunctions = caller.data().host;
+    // Bounds-checked over the guest's whole declared region, so a buffer running
+    // past memory is a wrong pointer rather than a truncated prefix being served…
+    let buf = mem
+        .data_mut(&mut *caller)
+        .get_mut(range)
+        .ok_or(HostError::PointerOutOfBounds)?;
+    // …of which only the field cap is writable, so no call can exceed it whatever
+    // the guest declared.
+    let buf = &mut buf[..cap.min(MAX_FIELD_BYTES)];
+
+    let n = fill(host, buf)?;
+
+    if n > MAX_FIELD_BYTES {
+        return Err(HostError::DataFieldTooLarge);
+    }
+    if n > cap {
+        return Err(HostError::BufferTooSmall);
+    }
+    charge_transfer(caller.data(), n)?;
+    #[expect(
+        clippy::cast_possible_truncation,
+        clippy::cast_possible_wrap,
+        reason = "`n > MAX_FIELD_BYTES` returned above, and the cap is far inside i32"
+    )]
+    let n = n as i32;
+    Ok(n)
+}
+
+/// Service a call that reads guest memory and writes bytes back to it: the host
+/// fills the run's output buffer, which is copied to the guest once every rule has
+/// passed.
+///
+/// `call` gets the guest's whole memory, so it can borrow any number of input
+/// regions with [`Region::read`] — which a `&mut` view of that memory would forbid.
+/// That is why the answer goes through a buffer instead of straight into the guest
+/// as [`write_into`]'s does.
+///
+/// **The host is never told the guest's capacity**: it is offered the whole buffer
+/// and reports the value's true length, so the fit is decided here, with nothing yet
+/// in guest memory. A refused value therefore reaches it in no part.
+///
+/// The output is judged after the inputs, so a call with both bad reports the
+/// input's verdict. `NoMemExported` precedes both: there is no memory to validate a
+/// region against.
+pub(crate) fn write_buffered(
+    caller: &mut Caller<'_, VmState<'_>>,
+    out: Region,
+    call: impl FnOnce(&dyn HostFunctions, &[u8], &mut [u8]) -> HostResult<usize>,
+) -> HostResult<i32> {
+    let mem = memory(caller)?;
+    // One borrow split in two: the guest's bytes for the inputs, the store data for
+    // the output buffer. Taking them together is what keeps the inputs borrowed
+    // rather than copied out.
+    let (data, state) = mem.data_and_store_mut(&mut *caller);
+    let host: &dyn HostFunctions = state.host;
+
+    let n = call(host, data, &mut state.out_buffer[..])?;
+
+    // `out` is checked here rather than before the call: the inputs are judged
+    // first, so a call with both malformed reports the input's verdict.
+    let range = out.range()?;
+    let cap = range.len();
+    if n > MAX_FIELD_BYTES {
+        return Err(HostError::DataFieldTooLarge);
+    }
+    let buf = data.get_mut(range).ok_or(HostError::PointerOutOfBounds)?;
+    if n > cap {
+        return Err(HostError::BufferTooSmall);
+    }
+    charge_transfer(state, n)?;
+    buf[..n].copy_from_slice(&state.out_buffer[..n]);
+    #[expect(
+        clippy::cast_possible_truncation,
+        clippy::cast_possible_wrap,
+        reason = "`n > MAX_FIELD_BYTES` returned above, and the cap is far inside i32"
+    )]
+    let n = n as i32;
+    Ok(n)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::vm::TRANSFER_LIMIT_BYTES;
+    use std::cell::Cell;
+    use wasmi::StoreLimitsBuilder;
+    use xrpl_host_functions::TraceDataType;
+
+    /// `charge_transfer` takes the store data, which has to hold a host.
+    struct UncalledHost;
+
+    impl HostFunctions for UncalledHost {
+        fn get_ledger_sqn(&self, _out: &mut [u8]) -> HostResult<usize> {
+            unreachable!("no unit test in this module calls the host")
+        }
+        fn get_current_ledger_obj_field(&self, _field: i32, _out: &mut [u8]) -> HostResult<usize> {
+            unreachable!("no unit test in this module calls the host")
+        }
+        fn sha512_half(&self, _data: &[u8], _out: &mut [u8]) -> HostResult<usize> {
+            unreachable!("no unit test in this module calls the host")
+        }
+        fn trace(&self, _msg: &str, _data: &[u8], _data_type: TraceDataType) -> HostResult<()> {
+            unreachable!("no unit test in this module calls the host")
+        }
+    }
+
+    fn state(budget: u64) -> VmState<'static> {
+        VmState {
+            host: &UncalledHost,
+            mem_limits: StoreLimitsBuilder::new().build(),
+            transfer_budget: Cell::new(budget),
+            memory: None,
+            out_buffer: [0u8; MAX_FIELD_BYTES],
+        }
+    }
+
+    /// `wasmi::Error` is not `PartialEq`, so a test expecting the guest-visible
+    /// channel says so by going through here.
+    fn wire(result: HostResult<i32>) -> i32 {
+        to_wire(result)
+            .unwrap_or_else(|trap| panic!("expected a guest-visible status, got a trap: {trap}"))
+    }
+
+    #[test]
+    fn a_success_becomes_the_value_and_an_error_becomes_its_code() {
+        assert_eq!(wire(Ok(0)), 0);
+        assert_eq!(wire(Ok(32)), 32);
+        assert_eq!(wire(Err(HostError::BufferTooSmall)), -3);
+    }
+
+    /// The fatal set as the tests *expect* it, not as [`is_fatal`] reports it:
+    /// deriving it from `is_fatal` would make both tests below vacuous, since a
+    /// condition wrongly classified as soft would simply be skipped.
+    const MUST_TRAP: [HostError; 3] = [
+        HostError::OutOfGas,
+        HostError::Internal,
+        HostError::NoMemExported,
+    ];
+
+    /// The trap carries the condition, so `run` can name the outcome without
+    /// parsing a message.
+    #[test]
+    fn a_host_fatal_error_becomes_a_trap_carrying_it() {
+        for error in MUST_TRAP {
+            let trap =
+                to_wire(Err(error)).expect_err("a fatal error must not reach the guest as a code");
+            let payload = trap.downcast_ref::<FatalHostError>().unwrap_or_else(|| {
+                panic!("{error:?}: expected a FatalHostError payload, got: {trap}")
+            });
+            assert_eq!(*payload, FatalHostError(error));
+        }
+    }
+
+    /// Over `HostError::ALL`, so it is the whole ABI and not a sample: a code added
+    /// to the ABI arrives already asserted to be guest-visible, and making it fatal
+    /// is then a change someone has to come and make.
+    ///
+    /// `OutOfTransferLimit` is the row worth reading twice: the one budget a
+    /// contract can be expected to handle, so it is told no rather than killed.
+    #[test]
+    fn only_the_host_fatal_errors_trap() {
+        for &error in HostError::ALL {
+            if MUST_TRAP.contains(&error) {
+                assert!(is_fatal(error), "{error:?} must stop the run");
+            } else {
+                assert!(!is_fatal(error), "{error:?} must reach the guest as a code");
+                assert_eq!(wire(Err(error)), error.code());
+            }
+        }
+    }
+
+    /// The result-less path splits the same set differently: the fatal errors still
+    /// stop the run, and every other one is dropped, since `trace` has no return value
+    /// to carry it. Over `HostError::ALL` for the reason above — a code added to the
+    /// ABI arrives asserted against both paths.
+    #[test]
+    fn a_call_with_no_result_drops_a_soft_error_and_traps_on_a_fatal_one() {
+        assert!(dropped(Ok(())).is_ok());
+
+        for &error in HostError::ALL {
+            if MUST_TRAP.contains(&error) {
+                let trap = dropped(Err(error)).expect_err("a fatal error must stop the run");
+                let payload = trap.downcast_ref::<FatalHostError>().unwrap_or_else(|| {
+                    panic!("{error:?}: expected a FatalHostError payload, got: {trap}")
+                });
+                assert_eq!(*payload, FatalHostError(error));
+            } else {
+                assert!(
+                    dropped(Err(error)).is_ok(),
+                    "{error:?} has no channel to the guest and must be dropped"
+                );
+            }
+        }
+    }
+
+    #[test]
+    fn a_transfer_spends_the_budget() {
+        let state = state(100);
+
+        assert_eq!(charge_transfer(&state, 30), Ok(()));
+        assert_eq!(state.transfer_budget.get(), 70);
+        assert_eq!(charge_transfer(&state, 70), Ok(()));
+        assert_eq!(state.transfer_budget.get(), 0);
+    }
+
+    /// The budget bounds the total, so the transfer that would overrun it is
+    /// refused whole rather than partially charged.
+    #[test]
+    fn a_transfer_past_the_budget_is_refused_and_charges_nothing() {
+        let state = state(100);
+
+        assert_eq!(
+            charge_transfer(&state, 101),
+            Err(HostError::OutOfTransferLimit)
+        );
+        assert_eq!(
+            state.transfer_budget.get(),
+            100,
+            "a refusal must not charge"
+        );
+        assert_eq!(charge_transfer(&state, 100), Ok(()));
+        assert_eq!(
+            charge_transfer(&state, 1),
+            Err(HostError::OutOfTransferLimit)
+        );
+    }
+
+    #[test]
+    fn transferring_nothing_costs_nothing() {
+        let state = state(0);
+
+        assert_eq!(charge_transfer(&state, 0), Ok(()));
+        assert_eq!(state.transfer_budget.get(), 0);
+    }
+
+    /// The field cap holds one call to a small share of the run's budget, so the
+    /// budget bounds a run rather than a call. An inequality, not the two values:
+    /// those are pinned in `vm.rs`.
+    #[test]
+    fn no_single_value_can_exhaust_the_run_budget() {
+        assert!(
+            (MAX_FIELD_BYTES as u64) * 64 <= TRANSFER_LIMIT_BYTES,
+            "one {MAX_FIELD_BYTES}-byte value against a {TRANSFER_LIMIT_BYTES}-byte budget"
+        );
+    }
+}
diff --git a/crates/xrpl-wasm-vm/src/lib.rs b/crates/xrpl-wasm-vm/src/lib.rs
new file mode 100644
index 00000000000..aae00006c81
--- /dev/null
+++ b/crates/xrpl-wasm-vm/src/lib.rs
@@ -0,0 +1,28 @@
+//! The escrow wasm VM: compile a contract, meter it, and serve its host calls.
+//!
+//! Every guest access goes through `abi.rs` and reaches linear memory only by
+//! wasmi's bounds-checked slice operations; `forbid(unsafe_code)` makes that a
+//! property rather than a claim. The cast lints are on for the same reason — on a
+//! consensus path a truncating or sign-losing cast changes what a contract is
+//! charged or told, so each one is argued for at its site.
+#![forbid(unsafe_code)]
+#![deny(rustdoc::broken_intra_doc_links)]
+#![deny(unreachable_pub)]
+#![deny(
+    clippy::cast_possible_truncation,
+    clippy::cast_possible_wrap,
+    clippy::cast_sign_loss,
+    clippy::cast_lossless
+)]
+
+mod abi;
+mod preflight;
+mod region;
+mod register;
+mod vm;
+
+pub use preflight::{CheckError, check};
+pub use vm::{
+    MAX_FIELD_BYTES, MAX_MEMORY_BYTES, MAX_MEMORY_PAGES, RunError, RunFailure, RunOutcome,
+    TRANSFER_LIMIT_BYTES, run,
+};
diff --git a/crates/xrpl-wasm-vm/src/preflight.rs b/crates/xrpl-wasm-vm/src/preflight.rs
new file mode 100644
index 00000000000..026d69b721b
--- /dev/null
+++ b/crates/xrpl-wasm-vm/src/preflight.rs
@@ -0,0 +1,351 @@
+//! Screening a contract before it reaches the ledger.
+//!
+//! [`check`] answers whether [`crate::run`] would refuse a module before the
+//! guest's first instruction — the three stages a caller maps to a malformed
+//! transaction rather than to a failed one. It needs **no host, no store and no
+//! gas**: everything it reads is a property of the compiled module. That is what
+//! makes it callable from a transaction's preflight, which has no ledger to serve
+//! host calls from.
+//!
+//! Two things it deliberately does not screen. A module exporting **no** linear
+//! memory passes: a contract that makes no host call needs none, and one that
+//! does is refused at the call and charged for what it burned. A start section
+//! passes: it is guest code, and executing it is the one thing a check must not do
+//! — a trap in one is charged to the contract like any other trap.
+//!
+//! One thing it screens that a run can only discover: an exported memory larger
+//! than the engine grants. See [`check_memory`] for what stays invisible.
+
+use std::fmt;
+use wasmi::{ExternType, FuncType, Module, ValType};
+use xrpl_host_functions::HostFunctionSpec;
+
+use crate::register::HOST_MODULE;
+use crate::vm::{MAX_MEMORY_PAGES, compile};
+
+/// Why a module cannot be run. One variant per stage, since the caller maps the
+/// stages separately.
+#[derive(Debug)]
+pub enum CheckError {
+    /// `wasm` is not a valid module under this engine's configuration.
+    Compile(String),
+    /// An import no engine of this ABI defines: another module namespace, a name
+    /// that is not a host function, or one imported as something other than a
+    /// function.
+    Import(String),
+    /// No export named `function_name` with signature `() -> i32`.
+    EntryPoint(String),
+    /// The module asks for more linear memory than the engine grants.
+    Memory(String),
+}
+
+impl fmt::Display for CheckError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            CheckError::Compile(detail) => write!(f, "compile: {detail}"),
+            CheckError::Import(detail) => write!(f, "import: {detail}"),
+            // The detail says which of the entry point's failures this is, since
+            // "no entry point" would be wrong for an export of the wrong type.
+            CheckError::EntryPoint(detail) => write!(f, "{detail}"),
+            CheckError::Memory(detail) => write!(f, "memory: {detail}"),
+        }
+    }
+}
+
+/// Screen `wasm`: it must compile, import only what the engine serves, export
+/// `function_name` as `() -> i32`, and ask for no more memory than it may have.
+///
+/// The stages are ordered by how much of the module each explains. An import fault
+/// is reported before a missing entry point because the imports are what the rest of
+/// the module is built on; memory comes last, being a resource request rather than a
+/// mistake about the ABI.
+pub fn check(wasm: &[u8], function_name: &str) -> Result<(), CheckError> {
+    let module = compile(wasm).map_err(CheckError::Compile)?;
+    check_imports(&module)?;
+    check_entry_point(&module, function_name)?;
+    check_memory(&module)
+}
+
+/// Every import must be one the linker defines. The first that is not ends the
+/// check, so a module with several faults reports the earliest.
+fn check_imports(module: &Module) -> Result<(), CheckError> {
+    for import in module.imports() {
+        check_import(import.module(), import.name(), import.ty()).map_err(CheckError::Import)?;
+    }
+    Ok(())
+}
+
+/// Whether the engine defines this one import.
+///
+/// The set of names is [`HostFunctionSpec::ALL`], which is also what
+/// [`crate::register::register_host_functions`] iterates — so a check and a run
+/// cannot disagree about which names exist, and adding a host function extends
+/// both at once. The one thing this does not compare is `ty`'s *signature*, which
+/// still parts a module from the engine at instantiation; the kind is compared
+/// because the engine defines these names as functions and as nothing else.
+///
+/// The rules are ordered, not merely alternatives: a guest importing `env::malloc`
+/// is told about the namespace rather than that `malloc` is not a host function,
+/// because the namespace is the one that explains every other import it has too.
+fn check_import(module: &str, name: &str, ty: &ExternType) -> Result<(), String> {
+    if module != HOST_MODULE {
+        return Err(format!("'{module}::{name}' is not from '{HOST_MODULE}'"));
+    }
+    if !HostFunctionSpec::ALL
+        .iter()
+        .any(|op| op.wasm_name() == name)
+    {
+        return Err(format!("no host function '{name}'"));
+    }
+    if !matches!(ty, ExternType::Func(_)) {
+        return Err(format!("'{HOST_MODULE}::{name}' is not a function"));
+    }
+    Ok(())
+}
+
+fn check_entry_point(module: &Module, name: &str) -> Result<(), CheckError> {
+    match module.get_export(name) {
+        Some(ExternType::Func(ty)) if is_entry_point(&ty) => Ok(()),
+        found => Err(CheckError::EntryPoint(entry_point_fault(found, name))),
+    }
+}
+
+/// The entry point's type: nothing in, one `i32` out — what [`crate::run`]'s
+/// `get_typed_func::<(), i32>` accepts.
+fn is_entry_point(ty: &FuncType) -> bool {
+    ty.params().is_empty() && matches!(ty.results(), [ValType::I32])
+}
+
+/// A module may not declare more linear memory than the engine grants.
+///
+/// Only what it *exports* is visible here. A memory a module keeps to itself is not
+/// in its exports, and the store's limiter is what refuses that one — at
+/// instantiation, where the run is charged nothing and the caller cannot tell it
+/// from any other resource failure. Screening the exported case covers every
+/// contract built against the guest SDK, since a contract needs an exported memory
+/// to make a host call at all.
+fn check_memory(module: &Module) -> Result<(), CheckError> {
+    for export in module.exports() {
+        if let ExternType::Memory(ty) = export.ty() {
+            check_initial_pages(ty.minimum()).map_err(CheckError::Memory)?;
+        }
+    }
+    Ok(())
+}
+
+/// Whether the engine will grant a memory of this declared initial size.
+///
+/// The *minimum* only: a declared maximum past the cap is legal and simply
+/// unreachable, which `vm_limits::a_declared_maximum_past_the_cap_is_allowed_but_
+/// unreachable` pins on the run side. Refusing it here would turn a runnable
+/// contract away.
+fn check_initial_pages(pages: u64) -> Result<(), String> {
+    if pages > u64::from(MAX_MEMORY_PAGES) {
+        return Err(format!(
+            "initial memory of {pages} pages is past the {MAX_MEMORY_PAGES}-page cap"
+        ));
+    }
+    Ok(())
+}
+
+/// How an entry-point lookup failed, in the words both stages use: a check and a
+/// run describe the same module the same way, and "no entry point" would send a
+/// contract author looking for a function they already have.
+pub(crate) fn entry_point_fault(found: Option<ExternType>, name: &str) -> String {
+    match found {
+        Some(ExternType::Func(_)) => {
+            format!("entry point '{name}' has the wrong signature, expected '() -> i32'")
+        }
+        Some(_) => format!("export '{name}' is not a function"),
+        None => format!("no entry point '{name}'"),
+    }
+}
+
+/// The rules, one by one, on inputs built directly rather than parsed out of a
+/// module. `tests/preflight.rs` runs real modules through [`check`]; what is here is
+/// what a module cannot state precisely — which rule fires, in which order, and in
+/// what words the caller logs it.
+///
+/// `wat` is a dev-dependency, so the one test here that does need a module writes it
+/// as text like every other test in the crate. What the library must not gain is a
+/// text *entry point* — `check` and `run` take binaries — and a `cfg(test)` caller
+/// cannot give it one.
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use wasmi::{GlobalType, MemoryType, Mutability};
+
+    /// A host function as a guest declares it. Any function type will do: the
+    /// signature is not what [`check_import`] compares.
+    fn a_function() -> ExternType {
+        ExternType::Func(FuncType::new([ValType::I32], [ValType::I32]))
+    }
+
+    /// A name every one of these tests can use, taken from the ABI rather than
+    /// spelled, so it stays a real host function as the ABI changes.
+    fn a_host_function_name() -> &'static str {
+        HostFunctionSpec::ALL[0].wasm_name()
+    }
+
+    // -----------------------------------------------------------------------
+    // Imports
+    // -----------------------------------------------------------------------
+
+    /// Every name the ABI declares is served. Derived from `ALL` rather than
+    /// listed, so a host function added to the ABI is covered the day it lands.
+    #[test]
+    fn every_declared_host_function_is_served() {
+        for op in HostFunctionSpec::ALL {
+            assert_eq!(
+                check_import(HOST_MODULE, op.wasm_name(), &a_function()),
+                Ok(()),
+                "{}",
+                op.wasm_name()
+            );
+        }
+    }
+
+    #[test]
+    fn an_import_from_another_namespace_is_refused() {
+        for namespace in ["env", "host", "host_lib2", ""] {
+            let refusal = check_import(namespace, a_host_function_name(), &a_function())
+                .expect_err(namespace);
+            assert!(
+                refusal.contains("is not from 'host_lib'"),
+                "{namespace}: {refusal}"
+            );
+        }
+    }
+
+    #[test]
+    fn an_unknown_name_is_refused() {
+        let refusal =
+            check_import(HOST_MODULE, "no_such_function", &a_function()).expect_err("unknown name");
+        assert_eq!(refusal, "no host function 'no_such_function'");
+    }
+
+    /// The engine defines these names as functions and as nothing else, so a module
+    /// importing one as a global or a memory does not link either.
+    #[test]
+    fn a_host_function_imported_as_anything_else_is_refused() {
+        for ty in [
+            ExternType::Global(GlobalType::new(ValType::I32, Mutability::Const)),
+            ExternType::Memory(MemoryType::new(1, None)),
+        ] {
+            let name = a_host_function_name();
+            let refusal = check_import(HOST_MODULE, name, &ty).expect_err("not a function");
+            assert_eq!(refusal, format!("'host_lib::{name}' is not a function"));
+        }
+    }
+
+    /// The rules are ordered. An import that breaks two of them is reported by the
+    /// first, so the message a contract author reads is the one that explains the
+    /// rest of their imports too.
+    #[test]
+    fn the_namespace_is_reported_before_the_name() {
+        let refusal = check_import("env", "no_such_function", &a_function())
+            .expect_err("neither the namespace nor the name is served");
+
+        assert!(refusal.contains("is not from 'host_lib'"), "{refusal}");
+        assert!(
+            !refusal.contains("no host function"),
+            "the namespace explains it: {refusal}"
+        );
+    }
+
+    /// Both halves of the type are load-bearing, and neither is checked anywhere
+    /// a module cannot reach.
+    #[test]
+    fn the_entry_point_type_is_nothing_in_and_one_i32_out() {
+        assert!(is_entry_point(&FuncType::new([], [ValType::I32])));
+
+        for wrong in [
+            FuncType::new([], []),
+            FuncType::new([], [ValType::I64]),
+            FuncType::new([ValType::I32], [ValType::I32]),
+            FuncType::new([], [ValType::I32, ValType::I32]),
+        ] {
+            assert!(!is_entry_point(&wrong), "{wrong:?}");
+        }
+    }
+
+    /// Three faults, three descriptions. A run reports these too, with wasmi's own
+    /// error appended, so a swapped arm would mislead at both stages at once.
+    #[test]
+    fn each_entry_point_fault_is_described_as_itself() {
+        assert_eq!(
+            entry_point_fault(Some(a_function()), "finish"),
+            "entry point 'finish' has the wrong signature, expected '() -> i32'"
+        );
+        assert_eq!(
+            entry_point_fault(
+                Some(ExternType::Global(GlobalType::new(
+                    ValType::I32,
+                    Mutability::Const
+                ))),
+                "finish"
+            ),
+            "export 'finish' is not a function"
+        );
+        assert_eq!(
+            entry_point_fault(None, "finish"),
+            "no entry point 'finish'",
+            "an absent export must not be reported as a wrong signature"
+        );
+    }
+
+    /// The cap itself is granted; one page past it is not. The boundary is the whole
+    /// rule, and it is the same boundary the store's limiter applies at
+    /// instantiation.
+    #[test]
+    fn the_initial_memory_may_reach_the_cap_but_not_pass_it() {
+        assert_eq!(check_initial_pages(0), Ok(()));
+        assert_eq!(check_initial_pages(u64::from(MAX_MEMORY_PAGES)), Ok(()));
+
+        let past = u64::from(MAX_MEMORY_PAGES) + 1;
+        let refusal = check_initial_pages(past).expect_err("one page past the cap");
+        assert_eq!(
+            refusal,
+            format!("initial memory of {past} pages is past the {MAX_MEMORY_PAGES}-page cap")
+        );
+    }
+
+    /// The bridge logs this string and the C++ tests match on it, so the stage's
+    /// prefix is part of the interface rather than a debugging aid.
+    #[test]
+    fn a_refusal_names_its_stage() {
+        assert_eq!(
+            CheckError::Compile("bad magic".to_string()).to_string(),
+            "compile: bad magic"
+        );
+        assert_eq!(
+            CheckError::Memory("initial memory of 129 pages".to_string()).to_string(),
+            "memory: initial memory of 129 pages"
+        );
+        assert_eq!(
+            CheckError::Import("no host function 'x'".to_string()).to_string(),
+            "import: no host function 'x'"
+        );
+        // The entry point's detail already says which of its three faults it is,
+        // so a prefix would only repeat it.
+        assert_eq!(
+            CheckError::EntryPoint("no entry point 'finish'".to_string()).to_string(),
+            "no entry point 'finish'"
+        );
+    }
+
+    #[test]
+    fn the_stages_run_in_order() {
+        assert!(
+            matches!(check(b"not wasm", "finish"), Err(CheckError::Compile(_))),
+            "nothing is screened until the module compiles"
+        );
+
+        // A module that compiles and imports nothing, so it reaches the entry point.
+        let empty = wat::parse_str("(module)").expect("assembles");
+        assert!(
+            matches!(check(&empty, "finish"), Err(CheckError::EntryPoint(_))),
+            "a module that compiles and imports nothing reaches the entry point"
+        );
+    }
+}
diff --git a/crates/xrpl-wasm-vm/src/region.rs b/crates/xrpl-wasm-vm/src/region.rs
new file mode 100644
index 00000000000..06268396c85
--- /dev/null
+++ b/crates/xrpl-wasm-vm/src/region.rs
@@ -0,0 +1,50 @@
+use crate::vm::MAX_FIELD_BYTES;
+use core::ops::Range;
+use xrpl_host_functions::{HostError, HostResult};
+
+/// A byte region as the guest declared it: the `(ptr, len)` pair off the wire, not
+/// yet checked.
+///
+/// Every byte parameter in this ABI is such a pair, so pairing them once at the wire
+/// boundary is what keeps the helpers in `abi.rs` from each taking two loose integers
+/// they could be handed in either order.
+///
+/// It lives in a module of its own so that the fields are out of reach and
+/// [`range`](Region::range) is the *only* way to indices — the check cannot be
+/// skipped, only deferred. Construction is infallible for that reason: a call whose
+/// output region is malformed is then refused in the order its own helper chooses,
+/// rather than at the moment the pair happened to be formed.
+#[derive(Copy, Clone)]
+pub(crate) struct Region {
+    ptr: i32,
+    len: i32,
+}
+
+impl Region {
+    pub(crate) fn new(ptr: i32, len: i32) -> Region {
+        Region { ptr, len }
+    }
+
+    /// `start..end` as indices. The conversion is the negativity check — it fails on
+    /// exactly the negative values — and the addition guards a 32-bit `usize`, where
+    /// two `i32`s can sum past the end.
+    pub(crate) fn range(self) -> HostResult<Range<usize>> {
+        let (Ok(start), Ok(len)) = (usize::try_from(self.ptr), usize::try_from(self.len)) else {
+            return Err(HostError::InvalidParams);
+        };
+        let end = start
+            .checked_add(len)
+            .ok_or(HostError::PointerOutOfBounds)?;
+        Ok(start..end)
+    }
+
+    /// The region's bytes, refused past the field cap. No copy: the slice aliases
+    /// `data`.
+    pub(crate) fn read(self, data: &[u8]) -> HostResult<&[u8]> {
+        let range = self.range()?;
+        if range.len() > MAX_FIELD_BYTES {
+            return Err(HostError::DataFieldTooLarge);
+        }
+        data.get(range).ok_or(HostError::PointerOutOfBounds)
+    }
+}
diff --git a/crates/xrpl-wasm-vm/src/register.rs b/crates/xrpl-wasm-vm/src/register.rs
new file mode 100644
index 00000000000..a3fac3824de
--- /dev/null
+++ b/crates/xrpl-wasm-vm/src/register.rs
@@ -0,0 +1,110 @@
+use crate::abi::{charged, charged_unreported, read_borrowed, write_buffered, write_into};
+use crate::region::Region;
+use crate::vm::VmState;
+use wasmi::{Caller, Linker};
+use xrpl_host_functions::{HostError, HostFunctionSpec, TraceDataType};
+
+/// The module name the guest imports under (`(import "host_lib" "ldgr_index" …)`),
+/// as the guest SDK and this fork's fixtures spell it.
+pub(crate) const HOST_MODULE: &str = "host_lib";
+
+/// Register the host functions on `linker`, one per [`HostFunctionSpec`] variant.
+///
+/// The `match` is exhaustive over [`HostFunctionSpec::ALL`], so a variant added to
+/// the ABI will not compile until it has an arm here — the "cannot forget to
+/// register" guarantee. Every arm goes through [`charged`], which is what makes the
+/// gas charge and the wire encoding unforgettable too.
+pub(crate) fn register_host_functions(
+    linker: &mut Linker<VmState<'_>>,
+) -> Result<(), wasmi::errors::LinkerError> {
+    // The arms are hand-written and repetitive by decision, not by neglect:
+    // generating them needs the typed `link_*` shims, deferred until the C header
+    // is generated from the same table.
+    for &op in HostFunctionSpec::ALL {
+        match op {
+            HostFunctionSpec::GetLedgerSqn => linker.func_wrap(
+                HOST_MODULE,
+                op.wasm_name(),
+                |mut caller: Caller<'_, VmState<'_>>,
+                 out_ptr: i32,
+                 out_len: i32|
+                 -> Result<i32, wasmi::Error> {
+                    charged(&mut caller, HostFunctionSpec::GetLedgerSqn, |c| {
+                        let out = Region::new(out_ptr, out_len);
+                        write_into(c, out, |host, out| host.get_ledger_sqn(out))
+                    })
+                },
+            ),
+            HostFunctionSpec::GetCurrentLedgerObjField => linker.func_wrap(
+                HOST_MODULE,
+                op.wasm_name(),
+                |mut caller: Caller<'_, VmState<'_>>,
+                 field: i32,
+                 out_ptr: i32,
+                 out_len: i32|
+                 -> Result<i32, wasmi::Error> {
+                    charged(
+                        &mut caller,
+                        HostFunctionSpec::GetCurrentLedgerObjField,
+                        |c| {
+                            let out = Region::new(out_ptr, out_len);
+                            write_into(c, out, |host, out| {
+                                host.get_current_ledger_obj_field(field, out)
+                            })
+                        },
+                    )
+                },
+            ),
+            HostFunctionSpec::Sha512Half => linker.func_wrap(
+                HOST_MODULE,
+                op.wasm_name(),
+                |mut caller: Caller<'_, VmState<'_>>,
+                 data_ptr: i32,
+                 data_len: i32,
+                 out_ptr: i32,
+                 out_len: i32|
+                 -> Result<i32, wasmi::Error> {
+                    charged(&mut caller, HostFunctionSpec::Sha512Half, |c| {
+                        let out = Region::new(out_ptr, out_len);
+                        let input = Region::new(data_ptr, data_len);
+                        write_buffered(c, out, |host, data, buf| {
+                            host.sha512_half(input.read(data)?, buf)
+                        })
+                    })
+                },
+            ),
+            // The one arm with no result: the wasm function is `(param i32 i32 i32 i32
+            // i32)` and nothing more, so a malformed call is dropped rather than
+            // answered — an unreadable region, a `msg` that is not UTF-8 and a
+            // `data_type` naming no rendering all leave the guest none the wiser, and
+            // the host uncalled.
+            //
+            // Also the one arm whose parameters are not the declaration's order:
+            // `data_type` arrives third, between the two regions, as xrpld and the
+            // guest stdlib spell it. The wasm order is this closure's; the declaration
+            // order is the call's.
+            HostFunctionSpec::Trace => linker.func_wrap(
+                HOST_MODULE,
+                op.wasm_name(),
+                |mut caller: Caller<'_, VmState<'_>>,
+                 msg_ptr: i32,
+                 msg_len: i32,
+                 data_type: i32,
+                 data_ptr: i32,
+                 data_len: i32|
+                 -> Result<(), wasmi::Error> {
+                    charged_unreported(&mut caller, HostFunctionSpec::Trace, |c| {
+                        let host = c.data().host;
+                        let msg = read_borrowed(c, Region::new(msg_ptr, msg_len))?;
+                        let msg = core::str::from_utf8(msg).map_err(|_| HostError::Decoding)?;
+                        let data_type =
+                            TraceDataType::from_code(data_type).ok_or(HostError::InvalidParams)?;
+                        let data = read_borrowed(c, Region::new(data_ptr, data_len))?;
+                        host.trace(msg, data, data_type)
+                    })
+                },
+            ),
+        }?;
+    }
+    Ok(())
+}
diff --git a/crates/xrpl-wasm-vm/src/vm.rs b/crates/xrpl-wasm-vm/src/vm.rs
new file mode 100644
index 00000000000..28643a819ed
--- /dev/null
+++ b/crates/xrpl-wasm-vm/src/vm.rs
@@ -0,0 +1,399 @@
+use std::cell::Cell;
+use std::fmt;
+use std::sync::LazyLock;
+use wasmi::{
+    Config, Engine, Export, Linker, Memory, Module, Store, StoreLimits, StoreLimitsBuilder,
+    TrapCode,
+};
+use xrpl_host_functions::{HostError, HostFunctions};
+
+use crate::abi::FatalHostError;
+use crate::preflight::entry_point_fault;
+use crate::register::register_host_functions;
+
+/// wasm linear-memory page size, fixed by the wasm spec (64 KiB).
+const WASM_PAGE_BYTES: u32 = 64 * 1024;
+
+/// Linear-memory page cap.
+pub const MAX_MEMORY_PAGES: u32 = 128;
+
+/// [`MAX_MEMORY_PAGES`] in bytes: 8 MiB.
+pub const MAX_MEMORY_BYTES: usize = (MAX_MEMORY_PAGES * WASM_PAGE_BYTES) as usize;
+
+/// Total bytes that may cross the host/guest boundary in one [`run`], separate
+/// from gas.
+pub const TRANSFER_LIMIT_BYTES: u64 = 1 << 20;
+
+/// Size cap on any single value crossing the boundary, in either direction; over
+/// it is `DataFieldTooLarge`.
+///
+/// A protocol limit: `kMaxWasmDataLength` in `include/xrpl/protocol/Protocol.h`.
+pub const MAX_FIELD_BYTES: usize = 1024;
+
+/// State threaded through every host call, stored in the wasmi [`Store`].
+pub(crate) struct VmState<'h> {
+    pub(crate) host: &'h dyn HostFunctions,
+    /// Enforces [`MAX_MEMORY_BYTES`] via `Store::limiter`, which needs a `&mut`
+    /// into it from `&mut VmState` — hence a field rather than a local.
+    pub(crate) mem_limits: StoreLimits,
+    /// Remaining transfer budget for this run ([`TRANSFER_LIMIT_BYTES`]).
+    ///
+    /// A `Cell` because it is decremented from a shared `&Caller`. One thread per
+    /// invocation touches the store, so the lack of `Sync` costs nothing.
+    ///
+    /// TODO: the extra charge for an unaligned field copy has nothing to attach to
+    /// until this ABI gains a `FieldLocator` host function.
+    pub(crate) transfer_budget: Cell<u64>,
+    /// The guest's linear memory, resolved once by [`run`] after instantiation so
+    /// no host call pays for an export lookup.
+    ///
+    /// Caching the handle is sound because a [`Memory`] is an arena index, not a
+    /// pointer to the bytes: it survives `memory.grow`, and `data`/`data_mut`
+    /// re-derive the slice per call.
+    ///
+    /// The handle is scoped to one store, so this assumes **one module, one
+    /// instance, one store per `run`**. Module linking or nested execution would
+    /// have to resolve per instance: a cached handle would serve a call against the
+    /// wrong instance's memory, which is a wrong answer rather than an error.
+    pub(crate) memory: Option<Memory>,
+    /// Where a host writes a value before [`crate::abi::write_buffered`] copies it
+    /// to the guest. One buffer per run, so no call zero-fills one of its own.
+    ///
+    /// Inline rather than boxed: the store's data is built once and then only
+    /// borrowed, so a kilobyte in it costs a move where a `Box` costs an
+    /// allocation. A local would cost neither, but `forbid(unsafe_code)` means a
+    /// stack buffer is zero-filled — per call, which is the cost this removes.
+    pub(crate) out_buffer: [u8; MAX_FIELD_BYTES],
+}
+
+/// Outcome of running an escrow contract to completion.
+#[derive(Debug)]
+pub struct RunOutcome {
+    /// The value returned by the exported entry point (`finish`): `> 0` means
+    /// allow the escrow to finish.
+    pub result: i32,
+    /// Fuel (gas) consumed by the whole invocation — guest instructions plus
+    /// the per-call host charges.
+    pub fuel_used: u64,
+}
+
+/// Why a run produced no result. Each variant is one outcome for the caller to
+/// map to a TER.
+#[derive(Debug)]
+pub enum RunError {
+    /// `wasm` is not a valid module under this engine's configuration.
+    Compile(String),
+    /// The module compiled but the engine would not accept it: an import the
+    /// linker does not define, or an initial memory past the page cap. Not guest
+    /// code failing — a start section that traps is [`RunError::Trap`].
+    Instantiate(String),
+    /// No export named `function_name` with signature `() -> i32`: absent, not a
+    /// function, or a function of another type — which the detail tells apart.
+    EntryPoint(String),
+    /// Gas exhausted — by the guest's own instructions or by a host call's
+    /// charge. [`RunFailure::fuel_used`] is the whole limit.
+    OutOfGas,
+    /// The host could not serve a call.
+    Internal,
+    /// A host call had no linear memory to work in: the module exports none, or
+    /// the call came from a start section, which runs before there is an instance
+    /// to resolve the memory from.
+    NoMemory,
+    /// The guest trapped: `unreachable`, division by zero, an out-of-bounds
+    /// access, or `memory.grow` past the page cap. Wherever the guest was
+    /// executing, including a start section during instantiation.
+    Trap(String),
+}
+
+impl fmt::Display for RunError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            RunError::Compile(detail) => write!(f, "compile: {detail}"),
+            RunError::Instantiate(detail) => write!(f, "instantiate: {detail}"),
+            // The detail says which of the entry point's failures this is, since
+            // "no entry point" would be wrong for an export of the wrong type.
+            RunError::EntryPoint(detail) => write!(f, "{detail}"),
+            RunError::OutOfGas => write!(f, "out of gas"),
+            RunError::Internal => write!(f, "internal error"),
+            RunError::NoMemory => write!(f, "no exported memory"),
+            RunError::Trap(detail) => write!(f, "trap: {detail}"),
+        }
+    }
+}
+
+/// A failed run, with the gas it still owes: a contract that traps or exhausts
+/// its gas is charged for what it burned.
+#[derive(Debug)]
+pub struct RunFailure {
+    pub error: RunError,
+    /// Fuel consumed before the failure. The whole limit when gas ran out; `0`
+    /// when the module never ran.
+    pub fuel_used: u64,
+}
+
+impl fmt::Display for RunFailure {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{} (fuel used: {})", self.error, self.fuel_used)
+    }
+}
+
+impl RunFailure {
+    /// A failure with no fuel accounted: it stopped the run at or before the guest's
+    /// first instruction, or under a store with no meter to read.
+    fn owing_nothing(error: RunError) -> RunFailure {
+        RunFailure {
+            error,
+            fuel_used: 0,
+        }
+    }
+}
+
+/// Fuel spent out of `gas`: the one place a run's cost is measured, so success,
+/// trap and refusal all report it the same way.
+///
+/// `Store::get_fuel` fails only on a store without fuel metering, which
+/// [`build_wasm_engine`] rules out and `run`'s `set_fuel` would already have
+/// caught — so a failure here is a defect in this crate. It must not become a
+/// number: `0` forgives a run its whole cost, `gas` charges an untouched one for
+/// everything. [`RunError::Internal`] instead.
+fn fuel_used(store: &Store<VmState<'_>>, gas: u64) -> Result<u64, RunError> {
+    store
+        .get_fuel()
+        .map(|remaining| gas.saturating_sub(remaining))
+        .map_err(|_| RunError::Internal)
+}
+
+/// Report `error` with the run's cost attached. A cost that cannot be read replaces
+/// the outcome rather than being invented — see [`fuel_used`].
+fn failed(store: &Store<VmState<'_>>, gas: u64, error: RunError) -> RunFailure {
+    match fuel_used(store, gas) {
+        Ok(fuel_used) => RunFailure { error, fuel_used },
+        Err(unmetered) => RunFailure::owing_nothing(unmetered),
+    }
+}
+
+/// The outcome a `wasmi::Error` names for itself, if any, rather than leaving it to
+/// the stage that raised it.
+///
+/// Two ways a run halts mid-flight: a host call that could not be served, which
+/// carries a [`FatalHostError`] saying which condition it was, and the guest's own
+/// instructions exhausting the meter, which wasmi raises as `OutOfFuel`.
+///
+/// Both can happen anywhere the guest executes — including a start section, which
+/// is guest code running during instantiation — so every stage from there on asks
+/// this before naming a failure after itself.
+fn guest_halted(error: &wasmi::Error) -> Option<RunError> {
+    if let Some(fatal) = error.downcast_ref::<FatalHostError>() {
+        return Some(host_fatal(fatal.0));
+    }
+    (error.as_trap_code() == Some(TrapCode::OutOfFuel)).then_some(RunError::OutOfGas)
+}
+
+/// Why instantiation failed, once [`guest_halted`] has ruled out the two conditions
+/// that can arise anywhere.
+///
+/// A start section is guest code, so it can trap on its own — `unreachable`, a
+/// division by zero, an out-of-bounds access — and a trap is the guest's fault
+/// wherever it happens. Naming that after the *stage* would file it beside the
+/// module faults a caller treats as its own defect, and charge nothing for
+/// instructions the contract burned. What is left for [`RunError::Instantiate`] is a
+/// module the linker or the store would not accept at all.
+fn instantiation_failure(error: &wasmi::Error) -> RunError {
+    match error.as_trap_code() {
+        Some(_) => RunError::Trap(error.to_string()),
+        None => RunError::Instantiate(error.to_string()),
+    }
+}
+
+/// The outcome a host-fatal `HostError` is.
+///
+/// Exhaustive rather than closed with a wildcard, so a variant added to the ABI
+/// must be placed here before this compiles. That is one direction of the agreement
+/// with [`crate::abi::is_fatal`], which picks the channel; the other — an existing
+/// variant moved into `is_fatal`'s set, landing in the soft arm and reported as
+/// `Internal` — is `tests::every_fatal_error_has_an_outcome_of_its_own`.
+///
+/// The soft arm is otherwise unreachable: a guest-visible error is a return code
+/// and never becomes a trap for [`guest_halted`] to unwrap.
+fn host_fatal(error: HostError) -> RunError {
+    match error {
+        HostError::OutOfGas => RunError::OutOfGas,
+        HostError::Internal => RunError::Internal,
+        HostError::NoMemExported => RunError::NoMemory,
+        HostError::FieldNotFound
+        | HostError::BufferTooSmall
+        | HostError::NoArray
+        | HostError::NotLeafField
+        | HostError::LocatorMalformed
+        | HostError::SlotOutRange
+        | HostError::SlotsFull
+        | HostError::EmptySlot
+        | HostError::LedgerObjNotFound
+        | HostError::Decoding
+        | HostError::DataFieldTooLarge
+        | HostError::PointerOutOfBounds
+        | HostError::InvalidParams
+        | HostError::InvalidAccount
+        | HostError::InvalidField
+        | HostError::IndexOutOfBounds
+        | HostError::FloatInputMalformed
+        | HostError::FloatComputationError
+        | HostError::NoRuntime
+        | HostError::OutOfTransferLimit => RunError::Internal,
+    }
+}
+
+/// The process-wide wasmi engine, built once on first use.
+///
+/// The configuration is consensus-fixed and identical for every invocation, and an
+/// [`Engine`] is an internally `Arc`ed `Send + Sync` handle, so one shared engine
+/// serves concurrent [`run`] calls.
+pub(crate) fn wasm_engine() -> &'static Engine {
+    static ENGINE: LazyLock<Engine> = LazyLock::new(build_wasm_engine);
+    &ENGINE
+}
+
+/// Build the wasmi engine the escrow VM requires: deterministic, minimal
+/// features, fuel metering on.
+fn build_wasm_engine() -> Engine {
+    let mut config = Config::default();
+    config.consume_fuel(true);
+    config.ignore_custom_sections(true);
+    config.wasm_mutable_global(false);
+    config.wasm_multi_value(false);
+    config.wasm_sign_extension(false);
+    config.wasm_saturating_float_to_int(false);
+    config.wasm_bulk_memory(false);
+    config.wasm_reference_types(false);
+    config.wasm_tail_call(false);
+    config.wasm_extended_const(false);
+    config.floats(false);
+    config.wasm_multi_memory(false);
+    config.wasm_custom_page_sizes(false);
+    config.wasm_memory64(false);
+    config.wasm_wide_arithmetic(false);
+    // TODO: enable option to reject wasm code containing start section after wasmi 2.0 release
+    Engine::new(&config)
+}
+
+/// Compile `wasm` for this engine.
+///
+/// The one path to a [`Module`]: the configuration is what decides whether a
+/// contract is valid at all, so [`run`] and [`crate::check`] must not be able to
+/// compile against different ones.
+pub(crate) fn compile(wasm: &[u8]) -> Result<Module, String> {
+    Module::new(wasm_engine(), wasm).map_err(|e| e.to_string())
+}
+
+/// Run a contract: compile `wasm`, give it `gas` fuel, service its host
+/// calls through `host`, and call the exported `function_name`.
+pub fn run<'h>(
+    wasm: &[u8],
+    gas: u64,
+    host: &'h dyn HostFunctions,
+    function_name: &str,
+) -> Result<RunOutcome, RunFailure> {
+    let engine = wasm_engine();
+    let module =
+        compile(wasm).map_err(|detail| RunFailure::owing_nothing(RunError::Compile(detail)))?;
+
+    let mem_limits = StoreLimitsBuilder::new()
+        .memory_size(MAX_MEMORY_BYTES)
+        .trap_on_grow_failure(true)
+        .build();
+    let mut store = Store::new(
+        engine,
+        VmState {
+            host,
+            mem_limits,
+            transfer_budget: Cell::new(TRANSFER_LIMIT_BYTES),
+            memory: None,
+            out_buffer: [0u8; MAX_FIELD_BYTES],
+        },
+    );
+
+    store
+        .set_fuel(gas)
+        .map_err(|_| RunFailure::owing_nothing(RunError::Internal))?;
+    store.limiter(|state| &mut state.mem_limits);
+
+    let mut linker = Linker::<VmState<'h>>::new(engine);
+    register_host_functions(&mut linker)
+        .map_err(|_| RunFailure::owing_nothing(RunError::Internal))?;
+
+    let instance = match linker.instantiate_and_start(&mut store, &module) {
+        Ok(instance) => instance,
+        Err(e) => {
+            let error = guest_halted(&e).unwrap_or_else(|| instantiation_failure(&e));
+            return Err(failed(&store, gas, error));
+        }
+    };
+    store.data_mut().memory = instance.exports(&store).find_map(Export::into_memory);
+
+    let function = match instance.get_typed_func::<(), i32>(&store, function_name) {
+        Ok(function) => function,
+        Err(e) => {
+            let found = instance
+                .get_export(&store, function_name)
+                .map(|export| export.ty(&store));
+            let error =
+                RunError::EntryPoint(format!("{}: {e}", entry_point_fault(found, function_name)));
+            return Err(failed(&store, gas, error));
+        }
+    };
+
+    let result = match function.call(&mut store, ()) {
+        Ok(result) => result,
+        Err(e) => {
+            let error = guest_halted(&e).unwrap_or_else(|| RunError::Trap(e.to_string()));
+            return Err(failed(&store, gas, error));
+        }
+    };
+
+    let fuel_used = fuel_used(&store, gas).map_err(RunFailure::owing_nothing)?;
+    Ok(RunOutcome { result, fuel_used })
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::abi::is_fatal;
+
+    #[test]
+    fn the_engine_is_one_engine() {
+        assert!(Engine::same(wasm_engine(), wasm_engine()));
+    }
+
+    #[test]
+    fn every_fatal_error_has_an_outcome_of_its_own() {
+        for &error in HostError::ALL {
+            let named = !matches!(host_fatal(error), RunError::Internal)
+                || matches!(error, HostError::Internal);
+            assert_eq!(
+                is_fatal(error),
+                named,
+                "{error:?}: abi::is_fatal {}, host_fatal {}",
+                if is_fatal(error) {
+                    "traps it"
+                } else {
+                    "passes it to the guest"
+                },
+                if named {
+                    "names its outcome"
+                } else {
+                    "groups it with the soft errors"
+                }
+            );
+        }
+    }
+
+    /// The only place these numbers appear as literals; every other test derives
+    /// them from the constants.
+    #[test]
+    fn the_limits_are_the_protocol_limits() {
+        assert_eq!(MAX_MEMORY_PAGES, 128, "linear-memory page cap");
+        assert_eq!(MAX_MEMORY_BYTES, 8 * 1024 * 1024, "page cap in bytes");
+        assert_eq!(MAX_FIELD_BYTES, 1024, "kMaxWasmDataLength");
+        assert_eq!(TRANSFER_LIMIT_BYTES, 1 << 20, "kWasmTransferLimit");
+    }
+}
diff --git a/crates/xrpl-wasm-vm/tests/budgets.rs b/crates/xrpl-wasm-vm/tests/budgets.rs
new file mode 100644
index 00000000000..5b5f4a99655
--- /dev/null
+++ b/crates/xrpl-wasm-vm/tests/budgets.rs
@@ -0,0 +1,467 @@
+//! The two budgets a run spends: gas (fuel), and the transfer limit on bytes
+//! crossing the boundary. Both are consensus input, so several of these tests
+//! assert exact numbers.
+
+mod support;
+
+use support::{
+    Answer, EMPTY_REGION, FakeHost, ONE_PAGE, PLENTY_OF_GAS, code, import, module, run,
+    run_with_gas, trace_call,
+};
+use xrpl_host_functions::{HASH_LEN, HostError, HostFunctionSpec, TraceDataType};
+use xrpl_wasm_vm::{MAX_FIELD_BYTES, RunError, TRANSFER_LIMIT_BYTES};
+
+// ---------------------------------------------------------------------------
+// Gas
+// ---------------------------------------------------------------------------
+
+/// The fuel a module of `body` burns, given gas to spare.
+fn fuel_for(body: &str, parts: &[&str], host: &FakeHost) -> u64 {
+    let wat = module(parts, body);
+    run(&wat, host).expect("the module should run").fuel_used
+}
+
+/// The fuel a module burns doing nothing but returning a constant; every figure
+/// below builds on it. wasmi's number, pinned deliberately because wasmi's fuel
+/// table is consensus input.
+const EMPTY_MODULE_FUEL: u64 = 30;
+
+/// wasmi's own fuel for a host call whose operands are all constants under 64: 14
+/// per `*.const`, plus 1 for the call. Our gas sits on top.
+///
+/// The formula holds only under 64, because wasmi widens a constant's encoding
+/// above that, each tier costing 7 more. Every call in [`call_for`] keeps its
+/// operands small for that reason; one with a larger constant fails here by a
+/// multiple of 7.
+fn wasmi_call_fuel(small_const_operands: u64) -> u64 {
+    14 * small_const_operands + 1
+}
+
+/// What wasmi charges on top of that for a call to a function with no result —
+/// `trace`'s shape, and nothing else in the ABI. Per call, not per module. Measured
+/// and pinned like the figures above.
+const WASMI_NO_RESULT_FUEL: u64 = 14;
+
+/// wasmi's fuel for one `(drop …)`, which is how a module makes more than one call
+/// and keeps only the last result. Pinned like the two above.
+const WASMI_DROP_FUEL: u64 = 21;
+
+/// The wasm a test needs in order to call one host function: the `(import …)`
+/// declaration, a call with small-constant operands, and how many it pushes.
+struct Call {
+    import: &'static str,
+    call: &'static str,
+    operands: u64,
+    /// Whether the call leaves an `i32` behind. `trace` does not, which is why
+    /// [`Call::body`] ends every module with a constant instead of the call.
+    yields: bool,
+}
+
+impl Call {
+    /// `n` calls in a row, leaving one `i32` for the module to return: the last
+    /// answer where there is one, and a constant where the call has none.
+    fn body(&self, n: usize) -> String {
+        if self.yields {
+            format!(
+                "{}{}",
+                format!("(drop {}) ", self.call).repeat(n - 1),
+                self.call
+            )
+        } else {
+            format!("{}(i32.const 0)", format!("{} ", self.call).repeat(n))
+        }
+    }
+
+    /// What [`Call::body`] burns beside the calls' own gas and the module's floor:
+    /// one `drop` between consecutive answers, or wasmi's own surcharge on a call
+    /// that has none.
+    fn overhead(&self, n: u64) -> u64 {
+        if self.yields {
+            (n - 1) * WASMI_DROP_FUEL
+        } else {
+            n * WASMI_NO_RESULT_FUEL
+        }
+    }
+}
+
+/// The test wasm for each host function. The `match` is exhaustive, so a function
+/// added to the ABI fails to compile until it has wasm here, and iterating
+/// [`HostFunctionSpec::ALL`] then covers the whole ABI.
+fn call_for(op: HostFunctionSpec) -> Call {
+    let (import, call, operands) = match op {
+        HostFunctionSpec::GetLedgerSqn => (
+            import::LDGR_INDEX,
+            "(call $ldgr_index (i32.const 0) (i32.const 4))",
+            2,
+        ),
+        HostFunctionSpec::GetCurrentLedgerObjField => (
+            import::HOME_LE_FIELD,
+            "(call $home_le_field (i32.const 1) (i32.const 0) (i32.const 4))",
+            3,
+        ),
+        HostFunctionSpec::Sha512Half => (
+            import::SHA512_HALF,
+            "(call $sha512_half (i32.const 0) (i32.const 4) (i32.const 0) (i32.const 32))",
+            4,
+        ),
+        HostFunctionSpec::Trace => (
+            import::TRACE,
+            "(call $trace (i32.const 0) (i32.const 0) (i32.const 1) (i32.const 0) (i32.const 0))",
+            5,
+        ),
+    };
+    Call {
+        import,
+        call,
+        operands,
+        yields: !matches!(op, HostFunctionSpec::Trace),
+    }
+}
+
+#[test]
+fn an_empty_module_burns_a_fixed_amount_of_fuel() {
+    let fuel = fuel_for("(i32.const 0)", &[ONE_PAGE], &FakeHost::new());
+    assert_eq!(fuel, EMPTY_MODULE_FUEL);
+}
+
+/// Calling a host function `n` times costs `n` times its gas, to the unit. Every
+/// other term is known — the module's floor, wasmi's fuel per call, one `drop` per
+/// answered call — so the total is a closed form, with the gas read from the spec
+/// table rather than restated. `n = 1` pins the charge, `n > 1` pins that it lands
+/// on every call rather than once per run.
+#[test]
+fn a_host_call_costs_its_gas_every_time_it_is_called() {
+    let host = FakeHost::new().answering_field(1, Answer::bytes([0xaa]));
+
+    for &op in HostFunctionSpec::ALL {
+        let call = call_for(op);
+        let per_call = wasmi_call_fuel(call.operands) + op.gas();
+
+        for n in 1..=3 {
+            let body = call.body(n);
+            let n = n as u64;
+
+            assert_eq!(
+                fuel_for(&body, &[call.import, ONE_PAGE], &host),
+                EMPTY_MODULE_FUEL + n * per_call + call.overhead(n),
+                "{n} x {}",
+                call.call
+            );
+        }
+    }
+}
+
+/// The gas charge precedes the call's body, so a failing call costs exactly what a
+/// successful one costs. Field 1 is answered and field 7 is not; the two modules
+/// are otherwise identical, so their totals are comparable.
+#[test]
+fn a_failing_host_call_costs_exactly_what_a_successful_one_costs() {
+    let host = FakeHost::new().answering_field(1, Answer::bytes([0xaa]));
+    let call = |field: i32| {
+        module(
+            &[import::HOME_LE_FIELD, ONE_PAGE],
+            &format!("(call $home_le_field (i32.const {field}) (i32.const 0) (i32.const 4))"),
+        )
+    };
+
+    let answered = run(&call(1), &host).expect("the module should run");
+    let refused = run(&call(7), &host).expect("the module should run");
+
+    assert_eq!(answered.result, 1);
+    assert_eq!(refused.result, code(HostError::FieldNotFound));
+    assert_eq!(refused.fuel_used, answered.fuel_used);
+}
+
+/// `fuel_used` is `gas - remaining`: what the run spent, not what was left or what
+/// it was handed. The gas figures are derived from the run's cost, so the boundary
+/// — exactly enough, and one short — is among the cases.
+#[test]
+fn fuel_used_is_what_was_spent_not_what_was_supplied() {
+    let host = FakeHost::new();
+    let op = HostFunctionSpec::GetLedgerSqn;
+    let call = call_for(op);
+    let wat = module(&[call.import, ONE_PAGE], call.call);
+    let cost = EMPTY_MODULE_FUEL + wasmi_call_fuel(call.operands) + op.gas();
+
+    // Exactly its cost is enough, and no amount above it changes the figure. The
+    // result is checked too, so the figure belongs to a run that did the work
+    // rather than to one that was cut short.
+    for gas in [cost, cost + 1, cost * 100, PLENTY_OF_GAS] {
+        let outcome = run_with_gas(&wat, gas, &host).expect("should run");
+        assert_eq!(
+            outcome.result, 4,
+            "gas {gas}: the call should have succeeded"
+        );
+        assert_eq!(outcome.fuel_used, cost, "gas {gas}");
+    }
+
+    // One fuel short: the run ends at the call it cannot pay for and still owes the
+    // whole limit, because `charge` spends what is left.
+    let short = run_with_gas(&wat, cost - 1, &host).expect_err("one fuel short must not complete");
+    assert!(
+        matches!(short.error, RunError::OutOfGas),
+        "expected the run to end out of gas, got: {short}"
+    );
+    assert_eq!(short.fuel_used, cost - 1);
+}
+
+/// Fuel is metered, so the same module burns the same fuel every time — a
+/// property consensus depends on.
+#[test]
+fn the_same_run_burns_the_same_fuel() {
+    let call = call_for(HostFunctionSpec::Trace);
+    let wat = module(&[call.import, ONE_PAGE], &call.body(1));
+
+    let first = run(&wat, &FakeHost::new()).expect("should run").fuel_used;
+    for _ in 0..4 {
+        assert_eq!(
+            run(&wat, &FakeHost::new()).expect("should run").fuel_used,
+            first
+        );
+    }
+    assert!(first > HostFunctionSpec::Trace.gas());
+}
+
+/// Too little gas to finish stops the run: the meter refuses the guest's own
+/// instructions before it ever reaches the host call.
+#[test]
+fn a_run_that_cannot_afford_itself_fails() {
+    let host = FakeHost::new();
+    let wat = module(
+        &[import::LDGR_INDEX, ONE_PAGE],
+        "(call $ldgr_index (i32.const 0) (i32.const 4))",
+    );
+
+    for gas in [0, 1, 10] {
+        let Err(failure) = run_with_gas(&wat, gas, &host) else {
+            panic!("gas {gas} should not have completed");
+        };
+        assert!(
+            matches!(failure.error, RunError::OutOfGas),
+            "gas {gas}: expected the run to end out of gas, got: {failure}"
+        );
+    }
+}
+
+/// A guest looping forever is stopped by gas rather than running away, and owes
+/// the gas it burned doing it.
+#[test]
+fn an_endless_loop_is_stopped_by_gas() {
+    const GAS: u64 = 100_000;
+
+    let host = FakeHost::new();
+    let wat = module(&[ONE_PAGE], "(loop $l (br $l)) (i32.const 0)");
+
+    let failure = run_with_gas(&wat, GAS, &host).expect_err("an endless loop must not complete");
+    assert!(
+        matches!(failure.error, RunError::OutOfGas),
+        "expected the meter to stop it, got: {failure}"
+    );
+    assert_eq!(
+        failure.fuel_used, GAS,
+        "a runaway guest burns the whole limit"
+    );
+}
+
+/// A host call refused its gas stops the run: the guest never gets a chance to
+/// ignore the refusal and carry on, and it is charged the whole limit.
+///
+/// The gas range is every amount that reaches the call and cannot pay for it, so
+/// the case is the whole boundary rather than one number. `trace` is the call under
+/// it because it is the one that could not report a refusal even if it wanted to:
+/// stopping the run is the whole of what the guest sees.
+#[test]
+fn a_host_call_refused_its_gas_stops_the_run() {
+    let host = FakeHost::new();
+    let op = HostFunctionSpec::Trace;
+    let call = call_for(op);
+    let wat = module(&[call.import, ONE_PAGE], &call.body(1));
+    // Measured rather than derived: the whole run's cost, less the call's own gas,
+    // is the least a guest can be given and still reach the call. Below that the
+    // meter stops the guest's own instructions instead, which is
+    // `a_run_that_cannot_afford_itself_fails`'s case, not this one.
+    let cost = run(&wat, &FakeHost::new())
+        .expect("the module should run")
+        .fuel_used;
+
+    for gas in cost - op.gas()..cost {
+        let Err(failure) = run_with_gas(&wat, gas, &host) else {
+            panic!("gas {gas}: the run completed, so the guest was handed the refusal");
+        };
+        assert!(
+            matches!(failure.error, RunError::OutOfGas),
+            "gas {gas}: expected the run to end out of gas, got: {failure}"
+        );
+        assert_eq!(
+            failure.fuel_used, gas,
+            "gas {gas}: a call it cannot afford burns the whole limit"
+        );
+    }
+    assert!(host.traces().is_empty(), "the host body must not have run");
+}
+
+// ---------------------------------------------------------------------------
+// The transfer limit
+// ---------------------------------------------------------------------------
+
+/// A module that repeats `call` while `keep_going` holds, then returns the last
+/// status, so a budget can be run to exhaustion inside one invocation.
+fn until_refused(imports: &str, call: &str, keep_going: &str) -> String {
+    module(
+        &[imports, ONE_PAGE],
+        &format!(
+            "(local $r i32)
+             (loop $l
+               (local.set $r {call})
+               (br_if $l {keep_going}))
+             (local.get $r)"
+        ),
+    )
+}
+
+/// For a call whose success is a positive byte count.
+const WHILE_POSITIVE: &str = "(i32.gt_s (local.get $r) (i32.const 0))";
+
+/// Bytes written into guest memory are charged against the run's budget, and the
+/// budget is a per-run total: 1 MiB of 1 KiB values exhausts it.
+#[test]
+fn writes_spend_the_transfer_budget() {
+    let host = FakeHost::new().answering_field(1, Answer::filler(MAX_FIELD_BYTES));
+    let wat = until_refused(
+        import::HOME_LE_FIELD,
+        &format!("(call $home_le_field (i32.const 1) (i32.const 0) (i32.const {MAX_FIELD_BYTES}))"),
+        WHILE_POSITIVE,
+    );
+
+    let outcome = run(&wat, &host).expect("the module should run");
+    assert_eq!(outcome.result, code(HostError::OutOfTransferLimit));
+    assert_eq!(
+        host.fields_asked.borrow().len() as u64,
+        TRANSFER_LIMIT_BYTES / MAX_FIELD_BYTES as u64 + 1,
+        "one call per 1 KiB of budget, plus the one that was refused"
+    );
+}
+
+/// The budget is per run, not per call: a fresh run starts with a full budget.
+#[test]
+fn each_run_gets_its_own_budget() {
+    let wat = until_refused(
+        import::HOME_LE_FIELD,
+        &format!("(call $home_le_field (i32.const 1) (i32.const 0) (i32.const {MAX_FIELD_BYTES}))"),
+        WHILE_POSITIVE,
+    );
+
+    for _ in 0..2 {
+        let host = FakeHost::new().answering_field(1, Answer::filler(MAX_FIELD_BYTES));
+        let outcome = run(&wat, &host).expect("the module should run");
+        assert_eq!(outcome.result, code(HostError::OutOfTransferLimit));
+        assert_eq!(
+            host.fields_asked.borrow().len() as u64,
+            TRANSFER_LIMIT_BYTES / MAX_FIELD_BYTES as u64 + 1
+        );
+    }
+}
+
+/// A run well inside the budget never sees it.
+#[test]
+fn a_modest_run_never_meets_the_budget() {
+    let host = FakeHost::new().answering_field(1, Answer::filler(MAX_FIELD_BYTES));
+    let wat = module(
+        &[import::HOME_LE_FIELD, ONE_PAGE],
+        &format!("(call $home_le_field (i32.const 1) (i32.const 0) (i32.const {MAX_FIELD_BYTES}))"),
+    );
+
+    let outcome = run(&wat, &host).expect("the module should run");
+    assert_eq!(outcome.result, MAX_FIELD_BYTES as i32);
+}
+
+/// Reads leave the budget alone: `read_borrowed` hands the host a slice *aliasing*
+/// guest memory, so there are no copied bytes to charge. What bounds how many reads
+/// a run can make is gas, which every host call pays before its body runs.
+///
+/// The observation is the write at the end, not the reads: the module reads four
+/// times the whole budget first, so a rule that charged reads would have nothing
+/// left, and the write would answer `OutOfTransferLimit` instead of a byte count.
+#[test]
+fn reads_do_not_spend_the_transfer_budget() {
+    /// 1 KiB reads, four times over the budget.
+    const READS: u64 = 4 * TRANSFER_LIMIT_BYTES / MAX_FIELD_BYTES as u64;
+
+    let host = FakeHost::new().answering_field(1, Answer::filler(MAX_FIELD_BYTES));
+    let read = trace_call(
+        TraceDataType::AsHex,
+        EMPTY_REGION,
+        &format!("(i32.const 0) (i32.const {MAX_FIELD_BYTES})"),
+    );
+    let wat = module(
+        &[import::TRACE, import::HOME_LE_FIELD, ONE_PAGE],
+        &format!(
+            "(local $i i32)
+             (loop $l
+               {read}
+               (local.set $i (i32.add (local.get $i) (i32.const 1)))
+               (br_if $l (i32.lt_u (local.get $i) (i32.const {READS}))))
+             (call $home_le_field (i32.const 1) (i32.const 0) (i32.const {MAX_FIELD_BYTES}))"
+        ),
+    );
+
+    let outcome = run(&wat, &host).expect("the module should run");
+    assert_eq!(
+        host.traces().len() as u64,
+        READS,
+        "every read should have been served"
+    );
+    assert_eq!(
+        outcome.result, MAX_FIELD_BYTES as i32,
+        "the write after {READS} reads of {MAX_FIELD_BYTES} bytes should still have its budget"
+    );
+}
+
+/// Only the output half of a read-write call spends the budget. `sha512_half`'s
+/// input is a borrowed read like any other, aliasing guest memory rather than
+/// crossing the boundary, so a run may hash far more bytes than the budget holds as
+/// long as the digests it writes fit inside it.
+///
+/// The two totals are asserted, so the arithmetic that makes the case is in the
+/// test rather than in a comment: the inputs alone would overrun the budget, the
+/// digests alone are a small fraction of it.
+#[test]
+fn only_the_output_half_of_a_read_write_spends_the_budget() {
+    /// Enough 1 KiB inputs to overrun the budget twice over.
+    const CALLS: u64 = 2 * TRANSFER_LIMIT_BYTES / MAX_FIELD_BYTES as u64;
+
+    assert!(
+        CALLS * MAX_FIELD_BYTES as u64 > TRANSFER_LIMIT_BYTES,
+        "the inputs alone must overrun the budget"
+    );
+    assert!(
+        CALLS * HASH_LEN as u64 <= TRANSFER_LIMIT_BYTES / 2,
+        "the digests alone must stay well inside it"
+    );
+
+    let host = FakeHost::new().answering_digest(Answer::filler(HASH_LEN));
+    let wat = module(
+        &[import::SHA512_HALF, ONE_PAGE],
+        &format!(
+            "(local $i i32)
+             (local $r i32)
+             (loop $l
+               (local.set $r (call $sha512_half (i32.const 0) (i32.const {MAX_FIELD_BYTES})
+                                                (i32.const 0) (i32.const {HASH_LEN})))
+               (local.set $i (i32.add (local.get $i) (i32.const 1)))
+               (br_if $l (i32.lt_u (local.get $i) (i32.const {CALLS}))))
+             (local.get $r)"
+        ),
+    );
+
+    let outcome = run(&wat, &host).expect("the module should run");
+    assert_eq!(
+        host.digested.borrow().len() as u64,
+        CALLS,
+        "every call should have been served"
+    );
+    assert_eq!(
+        outcome.result, HASH_LEN as i32,
+        "only the digests are charged, and they fit"
+    );
+}
diff --git a/crates/xrpl-wasm-vm/tests/host_calls.rs b/crates/xrpl-wasm-vm/tests/host_calls.rs
new file mode 100644
index 00000000000..b194ba7dad4
--- /dev/null
+++ b/crates/xrpl-wasm-vm/tests/host_calls.rs
@@ -0,0 +1,286 @@
+//! What each registered host function passes in each direction: the scalars the
+//! guest supplies reach the host unchanged, and the bytes the host produces land
+//! where the guest asked for them.
+
+mod support;
+
+use support::{
+    COMPLETED, EMPTY_REGION, FakeHost, ONE_PAGE, Trace, code, failure, import, module, run, status,
+    traced,
+};
+use xrpl_host_functions::{HASH_LEN, HostError, TraceDataType};
+use xrpl_wasm_vm::RunError;
+
+/// A value the host writes must be readable by the guest at the pointer it gave,
+/// and the call's status is the byte count.
+#[test]
+fn ldgr_index_writes_the_sequence_number_where_the_guest_asked() {
+    let host = FakeHost::new();
+
+    let wat = module(
+        &[import::LDGR_INDEX, ONE_PAGE],
+        "(drop (call $ldgr_index (i32.const 64) (i32.const 4)))
+         (i32.load (i32.const 64))",
+    );
+    assert_eq!(status(&wat, &host), 7, "the 4 LE bytes the host wrote");
+
+    let wat = module(
+        &[import::LDGR_INDEX, ONE_PAGE],
+        "(call $ldgr_index (i32.const 64) (i32.const 4))",
+    );
+    assert_eq!(status(&wat, &host), 4, "the byte count");
+}
+
+/// The output region is wherever the guest points, not a fixed address.
+#[test]
+fn the_output_region_is_the_pointer_the_guest_gave() {
+    let host = FakeHost::new();
+
+    for offset in [0, 1, 7, 4096, 65532] {
+        let wat = module(
+            &[import::LDGR_INDEX, ONE_PAGE],
+            &format!(
+                "(drop (call $ldgr_index (i32.const {offset}) (i32.const 4)))
+                 (i32.load (i32.const {offset}))"
+            ),
+        );
+        assert_eq!(status(&wat, &host), 7, "at offset {offset}");
+    }
+}
+
+/// A leading scalar parameter reaches the host as declared.
+#[test]
+fn home_le_field_passes_the_field_selector_through() {
+    let host = FakeHost::new().answering_field(17, support::Answer::bytes([0xab, 0xcd]));
+
+    let wat = module(
+        &[import::HOME_LE_FIELD, ONE_PAGE],
+        "(call $home_le_field (i32.const 17) (i32.const 0) (i32.const 64))",
+    );
+    assert_eq!(status(&wat, &host), 2);
+    assert_eq!(*host.fields_asked.borrow(), vec![17]);
+}
+
+/// A host error reaches the guest as its negative wire code, and the output
+/// region is left as the guest had it.
+#[test]
+fn a_host_error_becomes_its_wire_code() {
+    let host = FakeHost::new();
+    const UNTOUCHED: i32 = 7;
+
+    // Field 99 is unanswered, so the host returns `FieldNotFound`. The guest
+    // stamps its buffer first, then checks the byte survived the failed call.
+    let wat = module(
+        &[import::HOME_LE_FIELD, ONE_PAGE],
+        &format!(
+            "(i32.store8 (i32.const 0) (i32.const {UNTOUCHED}))
+             (drop (call $home_le_field (i32.const 99) (i32.const 0) (i32.const 64)))
+             (i32.load8_u (i32.const 0))"
+        ),
+    );
+    assert_eq!(status(&wat, &host), UNTOUCHED, "nothing was written");
+
+    let wat = module(
+        &[import::HOME_LE_FIELD, ONE_PAGE],
+        "(call $home_le_field (i32.const 99) (i32.const 0) (i32.const 64))",
+    );
+    assert_eq!(status(&wat, &host), code(HostError::FieldNotFound));
+}
+
+/// `sha512_half` reads one region and writes another in the same call.
+#[test]
+fn sha512_half_carries_bytes_in_and_out() {
+    const MARKER: u8 = 99;
+
+    let host = FakeHost::new().answering_digest(support::Answer::bytes([MARKER; HASH_LEN]));
+
+    let wat = module(
+        &[
+            import::SHA512_HALF,
+            ONE_PAGE,
+            r#"(data (i32.const 0) "hello wasm")"#,
+        ],
+        &format!(
+            "(drop (call $sha512_half (i32.const 0) (i32.const 10)
+                                      (i32.const 128) (i32.const {HASH_LEN})))
+             (i32.load8_u (i32.const 128))"
+        ),
+    );
+    assert_eq!(
+        status(&wat, &host),
+        i32::from(MARKER),
+        "the first digest byte"
+    );
+    assert_eq!(
+        *host.digested.borrow(),
+        vec![b"hello wasm".to_vec()],
+        "the input the host saw"
+    );
+}
+
+/// An empty input region is a legal read, not an error.
+#[test]
+fn sha512_half_accepts_an_empty_input() {
+    let host = FakeHost::new();
+
+    let wat = module(
+        &[import::SHA512_HALF, ONE_PAGE],
+        "(call $sha512_half (i32.const 0) (i32.const 0) (i32.const 128) (i32.const 32))",
+    );
+    assert_eq!(status(&wat, &host), 32);
+    assert_eq!(*host.digested.borrow(), vec![Vec::<u8>::new()]);
+}
+
+/// `trace` reads two regions and a type, and hands the guest back nothing — the
+/// module returns a constant of its own, which is what a completed run looks like.
+#[test]
+fn trace_passes_its_message_type_and_data_through() {
+    let host = FakeHost::new();
+
+    let wat = module(
+        &[
+            import::TRACE,
+            ONE_PAGE,
+            r#"(data (i32.const 0) "note")"#,
+            r#"(data (i32.const 16) "\01\02\03")"#,
+        ],
+        &traced(
+            TraceDataType::AsHex,
+            "(i32.const 0) (i32.const 4)",
+            "(i32.const 16) (i32.const 3)",
+        ),
+    );
+    assert_eq!(status(&wat, &host), COMPLETED);
+    assert_eq!(
+        host.traces(),
+        vec![Trace {
+            msg: "note".to_owned(),
+            data_type: TraceDataType::AsHex,
+            data: vec![1, 2, 3],
+        }]
+    );
+}
+
+/// The type is the guest's to choose and the host's to act on, so every code the
+/// ABI names has to arrive as the type it names.
+#[test]
+fn every_data_type_reaches_the_host_as_declared() {
+    for &data_type in TraceDataType::ALL {
+        let host = FakeHost::new();
+        let wat = module(
+            &[import::TRACE, ONE_PAGE],
+            &traced(data_type, EMPTY_REGION, EMPTY_REGION),
+        );
+        assert_eq!(status(&wat, &host), COMPLETED, "{data_type:?}");
+        assert_eq!(
+            host.traces().first().map(|t| t.data_type),
+            Some(data_type),
+            "{data_type:?}"
+        );
+    }
+}
+
+/// A code no type carries is the guest's mistake, and there is no channel to tell it
+/// so: the call is dropped and the run carries on.
+#[test]
+fn a_code_that_names_no_data_type_drops_the_call() {
+    for code in [0, -1, 8] {
+        let host = FakeHost::new();
+        let wat = module(
+            &[import::TRACE, ONE_PAGE],
+            &format!(
+                "(call $trace (i32.const 0) (i32.const 0) (i32.const {code}) (i32.const 0) (i32.const 0))
+                 (i32.const {COMPLETED})"
+            ),
+        );
+        assert_eq!(status(&wat, &host), COMPLETED, "code {code}");
+        assert!(
+            host.traces().is_empty(),
+            "code {code}: the host is not called"
+        );
+    }
+}
+
+/// A `&str` parameter is a byte region the engine validates: the host is handed
+/// a `&str`, so bytes that are not UTF-8 cannot be passed on.
+#[test]
+fn a_message_that_is_not_utf8_is_refused() {
+    let host = FakeHost::new();
+
+    let wat = module(
+        &[import::TRACE, ONE_PAGE, r#"(data (i32.const 0) "\ff\fe")"#],
+        &traced(
+            TraceDataType::AsText,
+            "(i32.const 0) (i32.const 2)",
+            EMPTY_REGION,
+        ),
+    );
+    assert_eq!(status(&wat, &host), COMPLETED);
+    assert!(host.traces().is_empty(), "the host must not be called");
+}
+
+/// The error a host with no result to report may still return: a soft one is the
+/// engine's to drop, since there is nowhere to put it and the contract asked
+/// nothing.
+#[test]
+fn a_soft_error_from_a_call_with_no_result_is_dropped() {
+    let host = FakeHost::new().failing_trace(HostError::InvalidParams);
+
+    let wat = module(
+        &[import::TRACE, ONE_PAGE],
+        &traced(TraceDataType::AsText, EMPTY_REGION, EMPTY_REGION),
+    );
+    assert_eq!(status(&wat, &host), COMPLETED);
+    assert_eq!(host.traces().len(), 1, "the host was called and failed");
+}
+
+/// A host-fatal error is not an answer to the call, so having no answer to give
+/// changes nothing: the run stops.
+#[test]
+fn a_fatal_error_from_a_call_with_no_result_still_stops_the_run() {
+    let host = FakeHost::new().failing_trace(HostError::Internal);
+
+    let wat = module(
+        &[import::TRACE, ONE_PAGE],
+        &traced(TraceDataType::AsText, EMPTY_REGION, EMPTY_REGION),
+    );
+    assert!(
+        matches!(failure(&wat, &host).error, RunError::Internal),
+        "a fatal host error must stop the run"
+    );
+}
+
+/// Several host calls in one run each see their own arguments: the two fields answer
+/// with distinct marker bytes and `finish` returns their sum, so a value landing in
+/// the wrong place gives a different total.
+#[test]
+fn calls_do_not_bleed_into_each_other() {
+    const FIRST: u8 = 11;
+    const SECOND: u8 = 22;
+
+    let host = FakeHost::new()
+        .answering_field(1, support::Answer::bytes([FIRST]))
+        .answering_field(2, support::Answer::bytes([SECOND, SECOND]));
+
+    let wat = module(
+        &[import::HOME_LE_FIELD, ONE_PAGE],
+        "(drop (call $home_le_field (i32.const 1) (i32.const 0) (i32.const 64)))
+         (drop (call $home_le_field (i32.const 2) (i32.const 64) (i32.const 64)))
+         (i32.add (i32.load8_u (i32.const 0)) (i32.load8_u (i32.const 64)))",
+    );
+    assert_eq!(status(&wat, &host), i32::from(FIRST) + i32::from(SECOND));
+    assert_eq!(*host.fields_asked.borrow(), vec![1, 2]);
+}
+
+/// The run's outcome carries the entry point's return value, and that value is
+/// the guest's own — the engine does not interpret it.
+#[test]
+fn the_outcome_carries_whatever_the_guest_returned() {
+    let host = FakeHost::new();
+
+    for value in [0, 1, -1, i32::MAX, i32::MIN] {
+        let wat = module(&[ONE_PAGE], &format!("(i32.const {value})"));
+        let outcome = run(&wat, &host).expect("the module should run");
+        assert_eq!(outcome.result, value);
+    }
+}
diff --git a/crates/xrpl-wasm-vm/tests/memory_policy.rs b/crates/xrpl-wasm-vm/tests/memory_policy.rs
new file mode 100644
index 00000000000..d8bc344ea47
--- /dev/null
+++ b/crates/xrpl-wasm-vm/tests/memory_policy.rs
@@ -0,0 +1,621 @@
+//! The bounds, field-cap and buffer-fit rules `abi.rs` enforces on every region
+//! crossing the boundary. This is the policy the guest observes, so each rule is
+//! pinned to the code it answers with.
+
+mod support;
+
+use support::{
+    Answer, COMPLETED, EMPTY_REGION, FakeHost, ONE_PAGE, code, failure, import, module, status,
+    traced,
+};
+use xrpl_host_functions::{HASH_LEN, HostError, TraceDataType};
+use xrpl_wasm_vm::{MAX_FIELD_BYTES, RunError};
+
+/// One page, so anything at or past 65536 is out of bounds.
+const PAGE: i64 = 64 * 1024;
+
+/// The per-field size cap, as a wasm operand.
+const CAP: i64 = MAX_FIELD_BYTES as i64;
+/// One byte over the cap: the smallest value the engine must refuse.
+const OVER_CAP: i64 = CAP + 1;
+
+// ---------------------------------------------------------------------------
+// Output regions (`write_into`)
+// ---------------------------------------------------------------------------
+
+/// The whole output region must be in bounds, not merely its start — the engine
+/// checks `[dst, dst + cap)` before the host is allowed to write.
+#[test]
+fn an_output_region_running_past_memory_is_refused() {
+    let host = FakeHost::new();
+
+    for (dst, cap) in [(PAGE, 4), (PAGE - 3, 4), (PAGE + 1024, 4), (0, PAGE + 1)] {
+        let wat = module(
+            &[import::LDGR_INDEX, ONE_PAGE],
+            &format!("(call $ldgr_index (i32.const {dst}) (i32.const {cap}))"),
+        );
+        assert_eq!(
+            status(&wat, &host),
+            code(HostError::PointerOutOfBounds),
+            "dst {dst} cap {cap}"
+        );
+    }
+}
+
+/// A region ending exactly at the last byte of memory is in bounds.
+#[test]
+fn an_output_region_ending_at_the_last_byte_is_allowed() {
+    let host = FakeHost::new();
+
+    let wat = module(
+        &[import::LDGR_INDEX, ONE_PAGE],
+        &format!("(call $ldgr_index (i32.const {}) (i32.const 4))", PAGE - 4),
+    );
+    assert_eq!(status(&wat, &host), 4);
+}
+
+/// The wire carries `i32`, so a guest can present a negative pointer or length.
+#[test]
+fn a_negative_output_pointer_or_length_is_refused() {
+    let host = FakeHost::new();
+
+    for (dst, cap) in [(-1, 4), (0, -1), (-1, -1), (i32::MIN, 4)] {
+        let wat = module(
+            &[import::LDGR_INDEX, ONE_PAGE],
+            &format!("(call $ldgr_index (i32.const {dst}) (i32.const {cap}))"),
+        );
+        assert_eq!(
+            status(&wat, &host),
+            code(HostError::InvalidParams),
+            "dst {dst} cap {cap}"
+        );
+    }
+}
+
+/// The host reports a value's true length whether or not it fitted; a value that
+/// did not fit is the guest's error, not the host's.
+#[test]
+fn a_value_larger_than_the_buffer_is_refused() {
+    let host = FakeHost::new().answering_field(1, Answer::filler(64));
+
+    let wat = module(
+        &[import::HOME_LE_FIELD, ONE_PAGE],
+        "(call $home_le_field (i32.const 1) (i32.const 0) (i32.const 63))",
+    );
+    assert_eq!(status(&wat, &host), code(HostError::BufferTooSmall));
+
+    let wat = module(
+        &[import::HOME_LE_FIELD, ONE_PAGE],
+        "(call $home_le_field (i32.const 1) (i32.const 0) (i32.const 64))",
+    );
+    assert_eq!(status(&wat, &host), 64, "exactly enough room is enough");
+}
+
+/// A zero-length output region is in bounds and simply cannot hold anything.
+#[test]
+fn a_zero_length_output_region_is_in_bounds_but_too_small() {
+    let host = FakeHost::new();
+
+    let wat = module(
+        &[import::LDGR_INDEX, ONE_PAGE],
+        "(call $ldgr_index (i32.const 0) (i32.const 0))",
+    );
+    assert_eq!(status(&wat, &host), code(HostError::BufferTooSmall));
+}
+
+/// A host that reports more than the per-field cap is refused even when the
+/// guest offered room for it: the cap is the engine's rule, not the buffer's.
+#[test]
+fn a_value_past_the_field_cap_is_refused() {
+    let host = FakeHost::new()
+        .answering_field(1, Answer::claiming(OVER_CAP as usize))
+        .answering_field(2, Answer::claiming(MAX_FIELD_BYTES));
+
+    let wat = module(
+        &[import::HOME_LE_FIELD, ONE_PAGE],
+        "(call $home_le_field (i32.const 1) (i32.const 0) (i32.const 4096))",
+    );
+    assert_eq!(status(&wat, &host), code(HostError::DataFieldTooLarge));
+
+    let wat = module(
+        &[import::HOME_LE_FIELD, ONE_PAGE],
+        "(call $home_le_field (i32.const 2) (i32.const 0) (i32.const 4096))",
+    );
+    assert_eq!(status(&wat, &host), CAP as i32, "the cap itself is allowed");
+}
+
+/// A refused over-cap value leaves nothing behind. `write_into` hands the host at
+/// most [`MAX_FIELD_BYTES`] of the guest's buffer however much room the guest
+/// declared, so a value past the cap does not fit the region it is offered and no
+/// prefix of it can reach guest memory either.
+///
+/// The host answers with a real over-cap value: [`Answer::claiming`] writes
+/// nothing whatever the engine does, so it could not tell the two apart. The
+/// second module folds the *whole* declared buffer rather than one byte, so the
+/// claim is about the region and not about its first byte.
+#[test]
+fn an_over_cap_value_is_refused_without_reaching_guest_memory() {
+    /// The buffer the guest declares: well over the cap, so the clamp bites.
+    const BUFFER: usize = 4096;
+
+    let over_cap = vec![0xff; MAX_FIELD_BYTES + 1];
+    let host = FakeHost::new().answering_field(1, Answer::bytes(over_cap));
+    let call = format!("(call $home_le_field (i32.const 1) (i32.const 0) (i32.const {BUFFER}))");
+
+    // The status the guest sees, from a module that returns it directly.
+    let refusing = module(&[import::HOME_LE_FIELD, ONE_PAGE], &call);
+    assert_eq!(
+        status(&refusing, &host),
+        code(HostError::DataFieldTooLarge),
+        "the value is refused"
+    );
+
+    // Every byte of the buffer, or-ed together: guest memory starts zero-filled,
+    // so any byte the host wrote shows up here.
+    let reading = module(
+        &[import::HOME_LE_FIELD, ONE_PAGE],
+        &format!(
+            "(local $i i32)
+             (local $seen i32)
+             (drop {call})
+             (loop $l
+               (local.set $seen (i32.or (local.get $seen) (i32.load8_u (local.get $i))))
+               (local.set $i (i32.add (local.get $i) (i32.const 1)))
+               (br_if $l (i32.lt_u (local.get $i) (i32.const {BUFFER}))))
+             (local.get $seen)"
+        ),
+    );
+    assert_eq!(
+        status(&reading, &host),
+        0,
+        "and not one of its bytes is in the guest's buffer"
+    );
+}
+
+/// The field cap is checked before the buffer-fit rule, so a value that breaks both
+/// is reported as over-cap. The guest branches on the code, and the two rules
+/// answer different questions, so the order is worth pinning.
+#[test]
+fn the_field_cap_precedes_the_buffer_fit_check() {
+    let host = FakeHost::new().answering_field(1, Answer::claiming(MAX_FIELD_BYTES + 1));
+
+    // A 63-byte buffer: the value is both over the cap and far too big to fit.
+    let wat = module(
+        &[import::HOME_LE_FIELD, ONE_PAGE],
+        "(call $home_le_field (i32.const 1) (i32.const 0) (i32.const 63))",
+    );
+    assert_eq!(status(&wat, &host), code(HostError::DataFieldTooLarge));
+}
+
+// ---------------------------------------------------------------------------
+// Input regions (`Region::read`, via `sha512_half`)
+//
+// `sha512_half`'s first pair is an input region like any other, and it is the
+// input the guest gets a status back from: `trace`, the other reader, answers
+// nothing at all. So the codes are pinned here and the silence below.
+// ---------------------------------------------------------------------------
+
+/// An input region is bounds-checked the same way an output region is. Every case
+/// here stays within the field cap, which on an input is checked first.
+#[test]
+fn an_input_region_running_past_memory_is_refused() {
+    let host = FakeHost::new();
+
+    for (ptr, len) in [(PAGE, 1), (PAGE - 3, 4), (PAGE - 1, CAP)] {
+        let wat = module(
+            &[import::SHA512_HALF, ONE_PAGE],
+            &format!(
+                "(call $sha512_half (i32.const {ptr}) (i32.const {len})
+                                    (i32.const 0) (i32.const {HASH_LEN}))"
+            ),
+        );
+        assert_eq!(
+            status(&wat, &host),
+            code(HostError::PointerOutOfBounds),
+            "ptr {ptr} len {len}"
+        );
+        assert!(host.digested.borrow().is_empty(), "the host is not called");
+    }
+}
+
+#[test]
+fn a_negative_input_pointer_or_length_is_refused() {
+    let host = FakeHost::new();
+
+    for (ptr, len) in [(-1, 1), (0, -1), (i32::MIN, 1)] {
+        let wat = module(
+            &[import::SHA512_HALF, ONE_PAGE],
+            &format!(
+                "(call $sha512_half (i32.const {ptr}) (i32.const {len})
+                                    (i32.const 0) (i32.const {HASH_LEN}))"
+            ),
+        );
+        assert_eq!(
+            status(&wat, &host),
+            code(HostError::InvalidParams),
+            "ptr {ptr} len {len}"
+        );
+    }
+}
+
+/// The field cap bounds what the guest may hand *in*, too.
+#[test]
+fn an_input_past_the_field_cap_is_refused() {
+    let host = FakeHost::new();
+    let digest = |len: i64| {
+        module(
+            &[import::SHA512_HALF, ONE_PAGE],
+            &format!(
+                "(call $sha512_half (i32.const 0) (i32.const {len})
+                                    (i32.const 2048) (i32.const {HASH_LEN}))"
+            ),
+        )
+    };
+
+    assert_eq!(
+        status(&digest(OVER_CAP), &host),
+        code(HostError::DataFieldTooLarge)
+    );
+    assert!(host.digested.borrow().is_empty());
+
+    assert_eq!(
+        status(&digest(CAP), &host),
+        HASH_LEN as i32,
+        "the cap itself is allowed"
+    );
+}
+
+/// The two directions check in opposite orders: an input's length is known before
+/// the read, so the cap comes first, while an output's region has to be resolved
+/// before the host can produce a value, so bounds come first there.
+#[test]
+fn the_field_cap_precedes_the_bounds_check_on_an_input() {
+    let host = FakeHost::new();
+
+    let reading = module(
+        &[import::SHA512_HALF, ONE_PAGE],
+        &format!(
+            "(call $sha512_half (i32.const 0) (i32.const {})
+                                (i32.const 0) (i32.const {HASH_LEN}))",
+            PAGE + 1
+        ),
+    );
+    assert_eq!(status(&reading, &host), code(HostError::DataFieldTooLarge));
+
+    let writing = module(
+        &[import::LDGR_INDEX, ONE_PAGE],
+        &format!("(call $ldgr_index (i32.const 0) (i32.const {}))", PAGE + 1),
+    );
+    assert_eq!(status(&writing, &host), code(HostError::PointerOutOfBounds));
+}
+
+// ---------------------------------------------------------------------------
+// The reader with no result (`read_borrowed`, via `trace`)
+// ---------------------------------------------------------------------------
+
+/// `trace` reads two regions and either one being bad refuses the call. The same
+/// rule as above, and the guest is told nothing: the refusal is the host not being
+/// called, and the run carries on to the constant that follows.
+#[test]
+fn both_of_traces_regions_are_checked_silently() {
+    let host = FakeHost::new();
+    let regions = [
+        (
+            format!("(i32.const {PAGE}) (i32.const 1)"),
+            EMPTY_REGION.to_owned(),
+        ),
+        (
+            EMPTY_REGION.to_owned(),
+            format!("(i32.const {PAGE}) (i32.const 1)"),
+        ),
+        (
+            EMPTY_REGION.to_owned(),
+            format!("(i32.const 0) (i32.const {OVER_CAP})"),
+        ),
+        (
+            "(i32.const -1) (i32.const 1)".to_owned(),
+            EMPTY_REGION.to_owned(),
+        ),
+    ];
+
+    for (msg, data) in regions {
+        let wat = module(
+            &[import::TRACE, ONE_PAGE],
+            &traced(TraceDataType::AsHex, &msg, &data),
+        );
+        assert_eq!(status(&wat, &host), COMPLETED, "msg {msg} data {data}");
+        assert!(
+            host.traces().is_empty(),
+            "msg {msg} data {data}: the host must not be called"
+        );
+    }
+}
+
+// ---------------------------------------------------------------------------
+// Both at once (`write_buffered`, via `sha512_half`)
+// ---------------------------------------------------------------------------
+
+/// A call with an input and an output region decides everything about the input
+/// before anything about the output, so a bad input is reported however the output
+/// region is wrong — out of bounds, or a pointer that is not one at all.
+///
+/// The whole output region, params included, is judged after the host has answered.
+/// Hoisting any part of that above the call would put the output's verdict first for
+/// these cases, and there is no half of it that can be hoisted on a principle the
+/// other half shares.
+#[test]
+fn a_read_write_checks_its_input_before_its_output() {
+    let host = FakeHost::new();
+    let digest = |src: i64, src_len: i64, dst: i64| {
+        module(
+            &[import::SHA512_HALF, ONE_PAGE],
+            &format!(
+                "(call $sha512_half (i32.const {src}) (i32.const {src_len})
+                                    (i32.const {dst}) (i32.const {HASH_LEN}))"
+            ),
+        )
+    };
+
+    let over_cap = digest(0, OVER_CAP, 0);
+    assert_eq!(status(&over_cap, &host), code(HostError::DataFieldTooLarge));
+
+    let out_of_bounds = digest(PAGE, 4, 0);
+    assert_eq!(
+        status(&out_of_bounds, &host),
+        code(HostError::PointerOutOfBounds)
+    );
+
+    // A bad input against each way the output can be wrong: the input's verdict is
+    // the one reported, and the host is never asked for a value nobody can take.
+    for dst in [PAGE, -1] {
+        let both_bad = digest(0, OVER_CAP, dst);
+        assert_eq!(
+            status(&both_bad, &host),
+            code(HostError::DataFieldTooLarge),
+            "dst {dst}"
+        );
+    }
+    assert!(host.digested.borrow().is_empty(), "the host is not reached");
+}
+
+/// The output half of a read-write call obeys the same rules as a plain write.
+#[test]
+fn a_read_write_output_obeys_the_write_rules() {
+    let host = FakeHost::new().answering_digest(Answer::filler(32));
+
+    let wat = module(
+        &[import::SHA512_HALF, ONE_PAGE],
+        "(call $sha512_half (i32.const 0) (i32.const 4) (i32.const 0) (i32.const 31))",
+    );
+    assert_eq!(status(&wat, &host), code(HostError::BufferTooSmall));
+
+    let wat = module(
+        &[import::SHA512_HALF, ONE_PAGE],
+        &format!(
+            "(call $sha512_half (i32.const 0) (i32.const 4) (i32.const {PAGE}) (i32.const 32))"
+        ),
+    );
+    assert_eq!(status(&wat, &host), code(HostError::PointerOutOfBounds));
+}
+
+/// A refused value reaches guest memory in no part, however much of it the host
+/// wrote. The host answers with 32 bytes it did write and a length it did not, so
+/// the refusal happens with the value sitting in the run's output buffer — and the
+/// guest's buffer has to come back untouched.
+///
+/// Stronger than the contract asks for: a guest must not read its buffer on a
+/// negative status. It holds because the buffer is copied to the guest only after
+/// the length, the bounds, the fit and the budget have all passed, so there is no
+/// window in which a refused value is in guest memory.
+#[test]
+fn a_refused_value_leaves_nothing_in_guest_memory() {
+    const MARKER: u8 = 77;
+
+    // The two refusals a value can meet after the host has produced it: longer
+    // than the field cap, and longer than the buffer the guest offered.
+    let refusals = [
+        (MAX_FIELD_BYTES + 1, HASH_LEN, HostError::DataFieldTooLarge),
+        (HASH_LEN, HASH_LEN - 1, HostError::BufferTooSmall),
+    ];
+
+    for (claimed, cap, expected) in refusals {
+        let host =
+            FakeHost::new().answering_digest(Answer::writing_but_claiming([MARKER; 32], claimed));
+        let call = format!(
+            "(call $sha512_half (i32.const 0) (i32.const 4) (i32.const 64) (i32.const {cap}))"
+        );
+
+        let refused = module(&[import::SHA512_HALF, ONE_PAGE], &call);
+        assert_eq!(
+            status(&refused, &host),
+            code(expected),
+            "claiming {claimed}"
+        );
+
+        // The same call, reporting what is at the output region afterwards.
+        let inspect = module(
+            &[import::SHA512_HALF, ONE_PAGE],
+            &format!("(drop {call}) (i32.load8_u (i32.const 64))"),
+        );
+        assert_eq!(
+            status(&inspect, &host),
+            0,
+            "claiming {claimed}: the refused value must not have been written"
+        );
+    }
+}
+
+/// An input region may overlap the output region: the host is served the input as
+/// it stands and its answer lands afterwards, so the two cannot interfere. The
+/// marker is any byte distinct from the input's first (`a`), so `finish` returning
+/// it proves the write landed.
+#[test]
+fn an_input_may_overlap_the_output() {
+    const MARKER: u8 = 99;
+
+    let host = FakeHost::new().answering_digest(Answer::bytes([MARKER; HASH_LEN]));
+
+    let wat = module(
+        &[
+            import::SHA512_HALF,
+            ONE_PAGE,
+            r#"(data (i32.const 0) "abcd")"#,
+        ],
+        &format!(
+            "(drop (call $sha512_half (i32.const 0) (i32.const 4)
+                                      (i32.const 0) (i32.const {HASH_LEN})))
+             (i32.load8_u (i32.const 0))"
+        ),
+    );
+    assert_eq!(
+        status(&wat, &host),
+        i32::from(MARKER),
+        "the output overwrote the input"
+    );
+    assert_eq!(
+        *host.digested.borrow(),
+        vec![b"abcd".to_vec()],
+        "the host saw the input as it was"
+    );
+}
+
+// ---------------------------------------------------------------------------
+// The memory export itself
+// ---------------------------------------------------------------------------
+
+/// A host call with no memory to work in ends the run instead of answering the
+/// guest: there is no buffer for a status to describe, and nothing the guest could
+/// do about the answer — which is what puts this beside out-of-gas on the fatal
+/// channel. What the guest burned getting there is still charged.
+fn assert_no_memory(wat: &str, host: &FakeHost) {
+    let failure = failure(wat, host);
+    assert!(
+        matches!(failure.error, RunError::NoMemory),
+        "expected the run to end for want of a memory export, got: {failure}"
+    );
+    assert!(failure.fuel_used > 0, "{failure}");
+}
+
+/// Every region is relative to the guest's exported memory, so a module without
+/// one cannot make a host call at all.
+#[test]
+fn a_module_that_exports_no_memory_cannot_call_the_host() {
+    let host = FakeHost::new();
+
+    let wat = module(
+        &[import::LDGR_INDEX, "(memory 1)"],
+        "(call $ldgr_index (i32.const 0) (i32.const 4))",
+    );
+    assert_no_memory(&wat, &host);
+}
+
+/// Having no memory is answered before anything about a call's arguments, so a
+/// module without one ends the run even when its arguments would have earned a
+/// guest-visible code of their own (here an input over the field cap).
+///
+/// The order is deliberate: no memory is a fact about the instance, not about this
+/// call, and a region cannot be validated against a memory that is not there. It
+/// costs the guest nothing — every call such a module makes ends the run anyway.
+#[test]
+fn no_memory_is_answered_before_a_calls_arguments_are() {
+    let host = FakeHost::new();
+
+    let wat = module(
+        &[import::SHA512_HALF, "(memory 1)"],
+        &format!(
+            "(call $sha512_half (i32.const 0) (i32.const {OVER_CAP})
+                                (i32.const 0) (i32.const {HASH_LEN}))"
+        ),
+    );
+    assert_no_memory(&wat, &host);
+}
+
+/// The memory's export *name* is not part of the contract: the engine takes the
+/// module's memory whatever it is called. Nothing in the wasm spec attaches meaning
+/// to `"memory"` — it is a toolchain convention, so the kind decides.
+#[test]
+fn a_memory_exported_under_any_name_is_the_guests_memory() {
+    let host = FakeHost::new();
+
+    for name in ["mem", "linear", "the memory"] {
+        let wat = module(
+            &[
+                import::LDGR_INDEX,
+                &format!(r#"(memory (export "{name}") 1)"#),
+            ],
+            "(drop (call $ldgr_index (i32.const 64) (i32.const 4)))
+             (i32.load (i32.const 64))",
+        );
+        assert_eq!(
+            status(&wat, &host),
+            7,
+            "the host wrote into the memory exported as '{name}'"
+        );
+    }
+}
+
+/// One memory exported under several names is one memory. The engine resolves the
+/// first export of kind memory, and with at most one memory per module every such
+/// export is that memory, so the order the exports are walked in cannot change the
+/// answer.
+#[test]
+fn one_memory_exported_under_several_names_is_still_that_memory() {
+    let host = FakeHost::new();
+
+    let wat = module(
+        &[
+            import::LDGR_INDEX,
+            r#"(memory (export "memory") (export "mem") (export "linear") 1)"#,
+        ],
+        "(drop (call $ldgr_index (i32.const 64) (i32.const 4)))
+         (i32.load (i32.const 64))",
+    );
+    assert_eq!(status(&wat, &host), 7);
+}
+
+/// The export has to *be* a memory: a global named `memory` is not one, and it
+/// neither serves as the guest's memory nor hides the memory the module really
+/// exports. The kind decides, so the conventional name carries no weight on
+/// either side.
+#[test]
+fn an_export_named_memory_that_is_not_a_memory_is_not_the_guests_memory() {
+    let host = FakeHost::new();
+
+    let call = "(call $ldgr_index (i32.const 0) (i32.const 4))";
+
+    let wrong_kind = module(
+        &[
+            import::LDGR_INDEX,
+            "(memory 1)",
+            r#"(global (export "memory") i32 (i32.const 0))"#,
+        ],
+        call,
+    );
+    assert_no_memory(&wrong_kind, &host);
+
+    let shadowed = module(
+        &[
+            import::LDGR_INDEX,
+            r#"(memory (export "mem") 1)"#,
+            r#"(global (export "memory") i32 (i32.const 0))"#,
+        ],
+        call,
+    );
+    assert_eq!(
+        status(&shadowed, &host),
+        4,
+        "the real memory is found past the global that took its name"
+    );
+}
+
+/// Bounds follow the memory the module actually declared, not a fixed page.
+#[test]
+fn bounds_follow_the_declared_memory_size() {
+    let host = FakeHost::new();
+
+    let wat = module(
+        &[import::LDGR_INDEX, r#"(memory (export "memory") 2)"#],
+        &format!("(call $ldgr_index (i32.const {PAGE}) (i32.const 4))"),
+    );
+    assert_eq!(status(&wat, &host), 4, "the second page is in bounds");
+}
diff --git a/crates/xrpl-wasm-vm/tests/preflight.rs b/crates/xrpl-wasm-vm/tests/preflight.rs
new file mode 100644
index 00000000000..8c30390fcfd
--- /dev/null
+++ b/crates/xrpl-wasm-vm/tests/preflight.rs
@@ -0,0 +1,459 @@
+//! What screening refuses, and that it refuses nothing a run would have served.
+//!
+//! `check` reaches its verdict from the compiled module alone, so these tests take
+//! no host — except the ones that put the same module through `run` to compare the
+//! two.
+
+mod support;
+
+use support::{ENTRY, FakeHost, ONE_PAGE, PLENTY_OF_GAS, assemble, import, module};
+use xrpl_host_functions::HostFunctionSpec;
+use xrpl_wasm_vm::{CheckError, MAX_MEMORY_PAGES, RunError};
+
+/// Assert which stage screening refused a module at, because the caller maps the
+/// stages separately. The error comes back out for the tests that also read its
+/// message.
+macro_rules! assert_stage {
+    ($refusal:expr, $stage:pat) => {{
+        let refusal = $refusal;
+        assert!(
+            matches!(refusal, $stage),
+            concat!("expected a ", stringify!($stage), " refusal, got: {}"),
+            refusal
+        );
+        refusal
+    }};
+}
+
+/// Screens `wat`, which must assemble.
+fn check(wat: &str) -> Result<(), CheckError> {
+    xrpl_wasm_vm::check(&assemble(wat), ENTRY)
+}
+
+fn refusal(wat: &str) -> CheckError {
+    check(wat).expect_err(&format!("expected this module to be refused:\n{wat}"))
+}
+
+fn passes(wat: &str) {
+    if let Err(refusal) = check(wat) {
+        panic!("expected this module to pass, but: {refusal}\n{wat}");
+    }
+}
+
+// ---------------------------------------------------------------------------
+// Compiling
+// ---------------------------------------------------------------------------
+
+/// A contract that imports a host function, exports its memory and exports the
+/// entry point is what screening is looking for.
+#[test]
+fn a_runnable_contract_passes() {
+    passes(&module(
+        &[import::LDGR_INDEX, ONE_PAGE],
+        "(call $ldgr_index (i32.const 0) (i32.const 4))",
+    ));
+}
+
+/// Bytes that are not a wasm module at all.
+#[test]
+fn garbage_does_not_pass() {
+    for bytes in [b"".as_slice(), b"not wasm", &[0x00, 0x61, 0x73, 0x6d]] {
+        let refusal = xrpl_wasm_vm::check(bytes, ENTRY).expect_err("garbage must not pass");
+        assert_stage!(refusal, CheckError::Compile(_));
+    }
+}
+
+/// Screening takes wasm binaries, and text is not one — the same rule the VM
+/// applies, from the same `wasmi` built without its `wat` feature. Turning that
+/// feature on would make this transaction blob valid at both ends.
+#[test]
+fn a_text_format_module_does_not_pass() {
+    let text = module(&[ONE_PAGE], "(i32.const 0)");
+
+    let refusal =
+        xrpl_wasm_vm::check(text.as_bytes(), ENTRY).expect_err("text must not pass as a module");
+    assert_stage!(refusal, CheckError::Compile(_));
+
+    // The same module, assembled first, passes: the text is sound and only the
+    // format was refused.
+    passes(&text);
+}
+
+/// A feature the engine disables is refused here too, because both stages compile
+/// against the one engine. `vm_limits.rs` walks every disabled feature; this pins
+/// that screening sees the same configuration.
+#[test]
+fn a_disabled_feature_does_not_pass() {
+    let refusal = refusal(&module(
+        &[ONE_PAGE],
+        "(drop (f64.add (f64.const 1) (f64.const 2))) (i32.const 0)",
+    ));
+    let refusal = assert_stage!(refusal, CheckError::Compile(_)).to_string();
+    assert!(refusal.contains("floating-point"), "{refusal}");
+}
+
+// ---------------------------------------------------------------------------
+// Imports
+// ---------------------------------------------------------------------------
+
+/// Every host function the ABI declares, spelled as a guest imports it. The count
+/// is asserted against the ABI so a function added to it cannot be left out here.
+const ALL_IMPORTS: [&str; 4] = [
+    import::LDGR_INDEX,
+    import::HOME_LE_FIELD,
+    import::SHA512_HALF,
+    import::TRACE,
+];
+
+#[test]
+fn every_declared_host_function_may_be_imported() {
+    assert_eq!(
+        ALL_IMPORTS.len(),
+        HostFunctionSpec::ALL.len(),
+        "the ABI gained a host function with no import declaration in this test"
+    );
+
+    let mut parts = ALL_IMPORTS.to_vec();
+    parts.push(ONE_PAGE);
+    passes(&module(&parts, "(i32.const 0)"));
+}
+
+/// A module may import fewer host functions than are registered, but not more.
+#[test]
+fn an_unknown_host_function_does_not_pass() {
+    let refusal = refusal(&module(
+        &[
+            r#"(import "host_lib" "no_such_function" (func $f (param i32) (result i32)))"#,
+            ONE_PAGE,
+        ],
+        "(call $f (i32.const 0))",
+    ));
+    let refusal = assert_stage!(refusal, CheckError::Import(_)).to_string();
+    assert!(
+        refusal.contains("no host function 'no_such_function'"),
+        "{refusal}"
+    );
+}
+
+/// Host functions live under one module name — `host_lib` — and an import naming
+/// another is refused even when the function name is real. `env` is in the list
+/// because that is what plain clang emits.
+#[test]
+fn an_import_from_another_module_does_not_pass() {
+    for module_name in ["host", "env", ""] {
+        let refusal = refusal(&module(
+            &[
+                &format!(
+                    r#"(import "{module_name}" "ldgr_index" (func $f (param i32 i32) (result i32)))"#
+                ),
+                ONE_PAGE,
+            ],
+            "(call $f (i32.const 0) (i32.const 4))",
+        ));
+        let refusal = assert_stage!(refusal, CheckError::Import(_)).to_string();
+        assert!(refusal.contains("is not from 'host_lib'"), "{refusal}");
+    }
+}
+
+/// A host function's name imported as something other than a function. The engine
+/// defines it as a function and nothing else, so this does not link either.
+#[test]
+fn a_host_function_imported_as_a_global_does_not_pass() {
+    let refusal = refusal(&module(
+        &[
+            r#"(import "host_lib" "ldgr_index" (global $g i32))"#,
+            ONE_PAGE,
+        ],
+        "(global.get $g)",
+    ));
+    let refusal = assert_stage!(refusal, CheckError::Import(_)).to_string();
+    assert!(
+        refusal.contains("'host_lib::ldgr_index' is not a function"),
+        "{refusal}"
+    );
+}
+
+/// A module faulty at two stages is refused by the earlier one — it imports what no
+/// engine serves *and* exports no entry point. The imports are what the rest of the
+/// module depends on, so that is the message worth having.
+#[test]
+fn the_earlier_stage_is_the_one_reported() {
+    let refusal = refusal(
+        r#"(module
+             (import "host_lib" "no_such_function" (func $f (result i32)))
+             (memory (export "memory") 1)
+             (func (export "not_the_entry_point") (result i32) (call $f)))"#,
+    );
+
+    assert_stage!(refusal, CheckError::Import(_));
+}
+
+/// The signature is the one part of an import screening does not compare, so a
+/// module that will not link can still pass. Recorded here because it is the gap
+/// this stage leaves, not because it is wanted.
+#[test]
+fn an_import_with_the_wrong_signature_still_passes() {
+    let wat = module(
+        &[
+            r#"(import "host_lib" "ldgr_index" (func $f (param i64 i64) (result i32)))"#,
+            ONE_PAGE,
+        ],
+        "(i32.const 0)",
+    );
+    passes(&wat);
+
+    let host = FakeHost::new();
+    let failure = xrpl_wasm_vm::run(&assemble(&wat), PLENTY_OF_GAS, &host, ENTRY)
+        .expect_err("a mistyped import must not link");
+    assert!(
+        matches!(failure.error, RunError::Instantiate(_)),
+        "{failure}"
+    );
+}
+
+// ---------------------------------------------------------------------------
+// The entry point
+// ---------------------------------------------------------------------------
+
+#[test]
+fn a_missing_entry_point_does_not_pass() {
+    let refusal = refusal(
+        r#"(module (memory (export "memory") 1)
+                              (func (export "other") (result i32) (i32.const 0)))"#,
+    );
+    let refusal = assert_stage!(refusal, CheckError::EntryPoint(_)).to_string();
+    assert_eq!(refusal, "no entry point 'finish'");
+}
+
+/// The entry point is looked up by the name the caller asks for, as a run looks it
+/// up: screening a contract for one entry point says nothing about another.
+#[test]
+fn the_entry_point_is_the_name_the_caller_gives() {
+    let wasm = assemble(
+        r#"(module (memory (export "memory") 1)
+             (func (export "other") (result i32) (i32.const 0)))"#,
+    );
+
+    assert!(xrpl_wasm_vm::check(&wasm, "other").is_ok());
+    assert!(xrpl_wasm_vm::check(&wasm, ENTRY).is_err());
+}
+
+/// Both halves of the entry point's type are screened: a module returning the
+/// wrong thing, or taking anything at all, would fail the run's typed lookup.
+#[test]
+fn an_entry_point_of_the_wrong_type_does_not_pass() {
+    for (signature, body) in [
+        ("(result i64)", "(i64.const 0)"),
+        ("(param i32) (result i32)", "(i32.const 0)"),
+        ("", "(nop)"),
+    ] {
+        let refusal = refusal(&format!(
+            r#"(module (memory (export "memory") 1)
+                 (func (export "finish") {signature} {body}))"#
+        ));
+        let refusal = assert_stage!(refusal, CheckError::EntryPoint(_)).to_string();
+        assert_eq!(
+            refusal, "entry point 'finish' has the wrong signature, expected '() -> i32'",
+            "{signature}"
+        );
+    }
+}
+
+/// An export of the entry point's name that is not a function at all is a third
+/// case, and named as such: nothing is missing and no signature is wrong.
+#[test]
+fn an_entry_point_that_is_not_a_function_does_not_pass() {
+    let refusal = refusal(
+        r#"(module (memory (export "memory") 1) (global (export "finish") i32 (i32.const 0)))"#,
+    );
+    let refusal = assert_stage!(refusal, CheckError::EntryPoint(_)).to_string();
+    assert_eq!(refusal, "export 'finish' is not a function");
+}
+
+// ---------------------------------------------------------------------------
+// Agreement with a run
+// ---------------------------------------------------------------------------
+
+/// A module with no linear memory to export passes. A contract that makes no host
+/// call needs none, and one that does is refused at the call and charged — a
+/// runtime fault, not a malformed module.
+#[test]
+fn a_module_exporting_no_memory_passes() {
+    let wat = r#"(module (func (export "finish") (result i32) (i32.const 0)))"#;
+    passes(wat);
+
+    let host = FakeHost::new();
+    assert_eq!(
+        xrpl_wasm_vm::run(&assemble(wat), PLENTY_OF_GAS, &host, ENTRY)
+            .expect("a module that calls no host function needs no memory")
+            .result,
+        0
+    );
+}
+
+/// Modules spanning what screening decides, each also put through a run.
+fn modules() -> Vec<(&'static str, String)> {
+    vec![
+        (
+            "a runnable contract",
+            module(&[import::LDGR_INDEX, ONE_PAGE], "(i32.const 0)"),
+        ),
+        (
+            "a contract that traps",
+            module(&[ONE_PAGE], "(unreachable)"),
+        ),
+        (
+            "a disabled feature",
+            module(&[ONE_PAGE], "(i32.extend8_s (i32.const 1))"),
+        ),
+        (
+            "an unknown host function",
+            module(
+                &[
+                    r#"(import "host_lib" "nope" (func $f (result i32)))"#,
+                    ONE_PAGE,
+                ],
+                "(call $f)",
+            ),
+        ),
+        (
+            "an import from another module",
+            module(
+                &[
+                    r#"(import "env" "ldgr_index" (func $f (param i32 i32) (result i32)))"#,
+                    ONE_PAGE,
+                ],
+                "(i32.const 0)",
+            ),
+        ),
+        (
+            "a host function imported as a global",
+            module(
+                &[r#"(import "host_lib" "trace" (global $g i32))"#, ONE_PAGE],
+                "(global.get $g)",
+            ),
+        ),
+        (
+            "no entry point",
+            r#"(module (memory (export "memory") 1)
+                 (func (export "other") (result i32) (i32.const 0)))"#
+                .to_string(),
+        ),
+        (
+            "an entry point of the wrong type",
+            r#"(module (memory (export "memory") 1)
+                 (func (export "finish") (result i64) (i64.const 0)))"#
+                .to_string(),
+        ),
+    ]
+}
+
+/// Screening refuses a module exactly when a run would refuse it at one of the
+/// three stages screening covers — nothing it rejects would have run, and nothing
+/// it passes stops before the entry point is called. The exceptions are the ones
+/// [`what_static_screening_cannot_see`] lists.
+#[test]
+fn screening_and_a_run_agree() {
+    let host = FakeHost::new();
+
+    for (label, wat) in modules() {
+        let wasm = assemble(&wat);
+        let refused_early = match xrpl_wasm_vm::run(&wasm, PLENTY_OF_GAS, &host, ENTRY) {
+            Err(failure) => matches!(
+                failure.error,
+                RunError::Compile(_) | RunError::Instantiate(_) | RunError::EntryPoint(_)
+            ),
+            Ok(_) => false,
+        };
+
+        assert_eq!(
+            xrpl_wasm_vm::check(&wasm, ENTRY).is_err(),
+            refused_early,
+            "{label}"
+        );
+    }
+}
+
+/// A module asking for more memory than the engine grants is refused, so the
+/// contract that could never run does not reach the ledger. The cap itself passes.
+#[test]
+fn an_exported_memory_past_the_cap_does_not_pass() {
+    let wat = module(
+        &[&format!(
+            r#"(memory (export "memory") {})"#,
+            MAX_MEMORY_PAGES + 1
+        )],
+        "(i32.const 0)",
+    );
+    let refusal = assert_stage!(refusal(&wat), CheckError::Memory(_)).to_string();
+    assert!(refusal.contains("past the 128-page cap"), "{refusal}");
+
+    passes(&module(
+        &[&format!(r#"(memory (export "memory") {MAX_MEMORY_PAGES})"#)],
+        "(i32.const 0)",
+    ));
+}
+
+/// A declared *maximum* past the cap is legal and simply unreachable, so screening
+/// must not turn it away: `vm_limits` runs this very module to completion.
+#[test]
+fn a_declared_maximum_past_the_cap_still_passes() {
+    passes(&module(
+        &[&format!(
+            r#"(memory (export "memory") 1 {})"#,
+            MAX_MEMORY_PAGES + 1
+        )],
+        "(i32.const 0)",
+    ));
+}
+
+/// The gap, listed rather than described, and now one entry long. A memory a module
+/// keeps to itself is not in its exports, so this is the one module that passes
+/// screening and then fails to *instantiate* — which is why a run's refusal at that
+/// stage cannot be read as the node's fault.
+///
+/// A contract needs an exported memory to make any host call, so a module of this
+/// shape can do nothing but compute; the SDK does not produce one.
+#[test]
+fn what_static_screening_cannot_see() {
+    let host = FakeHost::new();
+    let wat = format!(
+        r#"(module (memory {})
+             (func (export "finish") (result i32) (i32.const 0)))"#,
+        MAX_MEMORY_PAGES + 1
+    );
+
+    passes(&wat);
+
+    let failure = xrpl_wasm_vm::run(&assemble(&wat), PLENTY_OF_GAS, &host, ENTRY)
+        .expect_err("the store's limiter must refuse the memory");
+    assert!(
+        matches!(failure.error, RunError::Instantiate(_)),
+        "{failure}"
+    );
+}
+
+/// A start section is guest code, so screening cannot see whether it traps — but it
+/// no longer has to. A trap is the guest's fault wherever it happens, so the run
+/// charges the contract for what it burned instead of reporting a module the node
+/// should have screened.
+#[test]
+fn a_start_section_screening_cannot_see_is_charged_as_a_trap() {
+    let host = FakeHost::new();
+    let wat = format!(
+        r#"(module {ONE_PAGE}
+             (func $init (unreachable))
+             (start $init)
+             (func (export "finish") (result i32) (i32.const 0)))"#
+    );
+
+    passes(&wat);
+
+    let failure = xrpl_wasm_vm::run(&assemble(&wat), PLENTY_OF_GAS, &host, ENTRY)
+        .expect_err("a start section that traps must not complete the run");
+    assert!(matches!(failure.error, RunError::Trap(_)), "{failure}");
+    assert!(
+        failure.fuel_used > 0,
+        "charged for what it burned: {failure}"
+    );
+}
diff --git a/crates/xrpl-wasm-vm/tests/support/mod.rs b/crates/xrpl-wasm-vm/tests/support/mod.rs
new file mode 100644
index 00000000000..32b9dfe83a3
--- /dev/null
+++ b/crates/xrpl-wasm-vm/tests/support/mod.rs
@@ -0,0 +1,302 @@
+//! Shared scaffolding for the integration tests: a host whose every answer the
+//! test sets, and the pieces of a wasm module to run against it.
+//!
+//! `abi.rs`'s guest-memory marshaling is reachable only from a live host call, so
+//! each test assembles the smallest module that exercises one rule and reads the
+//! verdict out of `finish`'s return value.
+
+#![allow(dead_code)] // Each test binary uses a different part of this module.
+
+use std::cell::RefCell;
+use std::collections::HashMap;
+
+use xrpl_host_functions::{HostError, HostFunctions, HostResult, TraceDataType};
+use xrpl_wasm_vm::{RunFailure, RunOutcome};
+
+/// The entry point every test module exports.
+pub const ENTRY: &str = "finish";
+
+/// Gas for a test that is not about gas: enough that nothing runs out.
+pub const PLENTY_OF_GAS: u64 = 100_000_000;
+
+// ---------------------------------------------------------------------------
+// The fake host
+// ---------------------------------------------------------------------------
+
+/// What the host does when asked for a value.
+#[derive(Clone, Debug)]
+pub enum Answer {
+    /// Writes `bytes` into the output region if they fit, and reports `len` as
+    /// the true length either way. `len` is separate from `bytes.len()` so a
+    /// test can reach the over-cap and buffer-fit rules without a value that
+    /// large.
+    Value { bytes: Vec<u8>, len: usize },
+    /// Fails without touching the output region.
+    Fail(HostError),
+}
+
+impl Answer {
+    /// Writes `bytes` and reports their true length.
+    pub fn bytes(bytes: impl Into<Vec<u8>>) -> Answer {
+        let bytes = bytes.into();
+        Answer::Value {
+            len: bytes.len(),
+            bytes,
+        }
+    }
+
+    /// Writes nothing and claims a value of `len` bytes. It under-writes relative
+    /// to a real host, which writes whenever the value fits `out`, so a test about
+    /// what lands in guest memory wants [`Answer::bytes`] instead.
+    pub fn claiming(len: usize) -> Answer {
+        Answer::Value {
+            bytes: Vec::new(),
+            len,
+        }
+    }
+
+    /// Writes `bytes` and reports `len` regardless — a host whose value is longer
+    /// than what it put in the buffer, which the engine has to refuse without
+    /// letting those bytes reach the guest.
+    pub fn writing_but_claiming(bytes: impl Into<Vec<u8>>, len: usize) -> Answer {
+        Answer::Value {
+            bytes: bytes.into(),
+            len,
+        }
+    }
+
+    /// `len` bytes counting up from 0, written and reported.
+    pub fn filler(len: usize) -> Answer {
+        Answer::bytes((0..len).map(|i| i as u8).collect::<Vec<u8>>())
+    }
+
+    fn fill(&self, out: &mut [u8]) -> HostResult<usize> {
+        match self {
+            Answer::Value { bytes, len } => {
+                if bytes.len() <= out.len() {
+                    out[..bytes.len()].copy_from_slice(bytes);
+                }
+                Ok(*len)
+            }
+            Answer::Fail(error) => Err(*error),
+        }
+    }
+}
+
+/// One `trace` call, as the host received it.
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct Trace {
+    pub msg: String,
+    pub data_type: TraceDataType,
+    pub data: Vec<u8>,
+}
+
+/// A `HostFunctions` implementation that answers from what the test put in it and
+/// records what it was asked. The ABI's receiver is `&self`, so the recording goes
+/// behind `RefCell`, as a real mutating host's would.
+pub struct FakeHost {
+    /// What `get_ledger_sqn` answers.
+    pub ledger_sqn: Answer,
+    /// What `get_current_ledger_obj_field` answers, by field selector. An
+    /// unlisted selector answers `FieldNotFound`.
+    pub fields: HashMap<i32, Answer>,
+    /// What `sha512_half` answers, whatever it is given.
+    pub digest: Answer,
+    /// Every field selector `get_current_ledger_obj_field` was asked for.
+    pub fields_asked: RefCell<Vec<i32>>,
+    /// Every input `sha512_half` was given.
+    pub digested: RefCell<Vec<Vec<u8>>>,
+    /// Every `trace` call, in order.
+    pub traces: RefCell<Vec<Trace>>,
+    /// What `trace` fails with, after recording the call. `trace` has no result,
+    /// so this is how a test reaches what the engine does with an error it cannot
+    /// report.
+    pub trace_failure: Option<HostError>,
+}
+
+impl Default for FakeHost {
+    fn default() -> FakeHost {
+        FakeHost {
+            // 4 little-endian bytes, as the declaration's doc comment specifies.
+            ledger_sqn: Answer::bytes(7u32.to_le_bytes()),
+            fields: HashMap::new(),
+            digest: Answer::filler(32),
+            fields_asked: RefCell::new(Vec::new()),
+            digested: RefCell::new(Vec::new()),
+            traces: RefCell::new(Vec::new()),
+            trace_failure: None,
+        }
+    }
+}
+
+impl FakeHost {
+    pub fn new() -> FakeHost {
+        FakeHost::default()
+    }
+
+    pub fn answering_sqn(mut self, answer: Answer) -> FakeHost {
+        self.ledger_sqn = answer;
+        self
+    }
+
+    pub fn answering_field(mut self, field: i32, answer: Answer) -> FakeHost {
+        self.fields.insert(field, answer);
+        self
+    }
+
+    pub fn answering_digest(mut self, answer: Answer) -> FakeHost {
+        self.digest = answer;
+        self
+    }
+
+    pub fn failing_trace(mut self, error: HostError) -> FakeHost {
+        self.trace_failure = Some(error);
+        self
+    }
+
+    pub fn traces(&self) -> Vec<Trace> {
+        self.traces.borrow().clone()
+    }
+}
+
+impl HostFunctions for FakeHost {
+    fn get_ledger_sqn(&self, out: &mut [u8]) -> HostResult<usize> {
+        self.ledger_sqn.fill(out)
+    }
+
+    fn get_current_ledger_obj_field(&self, field: i32, out: &mut [u8]) -> HostResult<usize> {
+        self.fields_asked.borrow_mut().push(field);
+        match self.fields.get(&field) {
+            Some(answer) => answer.fill(out),
+            None => Err(HostError::FieldNotFound),
+        }
+    }
+
+    fn sha512_half(&self, data: &[u8], out: &mut [u8]) -> HostResult<usize> {
+        self.digested.borrow_mut().push(data.to_vec());
+        self.digest.fill(out)
+    }
+
+    /// Records before failing, so a test can tell a host that was called and then
+    /// failed from one that was never reached.
+    fn trace(&self, msg: &str, data: &[u8], data_type: TraceDataType) -> HostResult<()> {
+        self.traces.borrow_mut().push(Trace {
+            msg: msg.to_owned(),
+            data_type,
+            data: data.to_vec(),
+        });
+        match self.trace_failure {
+            Some(error) => Err(error),
+            None => Ok(()),
+        }
+    }
+}
+
+// ---------------------------------------------------------------------------
+// Module pieces
+// ---------------------------------------------------------------------------
+
+/// One `(import …)` declaration per host function, spelled with the module name
+/// and signature it is registered under and binding the `$name` call sites use. A
+/// wrong module name or signature fails instantiation.
+pub mod import {
+    pub const LDGR_INDEX: &str =
+        r#"(import "host_lib" "ldgr_index" (func $ldgr_index (param i32 i32) (result i32)))"#;
+    pub const HOME_LE_FIELD: &str = r#"(import "host_lib" "home_le_field" (func $home_le_field (param i32 i32 i32) (result i32)))"#;
+    pub const SHA512_HALF: &str = r#"(import "host_lib" "sha512_half" (func $sha512_half (param i32 i32 i32 i32) (result i32)))"#;
+    /// No result, unlike every other import here: `trace` answers the guest nothing.
+    pub const TRACE: &str =
+        r#"(import "host_lib" "trace" (func $trace (param i32 i32 i32 i32 i32)))"#;
+}
+
+/// One page of linear memory, exported under the name the engine looks for.
+pub const ONE_PAGE: &str = r#"(memory (export "memory") 1)"#;
+
+/// What a module returns after a `trace`: the call leaves nothing on the stack, so a
+/// test asserting on the run rather than on an answer asserts this.
+pub const COMPLETED: i32 = 1;
+
+/// A `(ptr, len)` pair naming no bytes, for the half of a `trace` a test is not
+/// about.
+pub const EMPTY_REGION: &str = "(i32.const 0) (i32.const 0)";
+
+/// A `trace` of `data` as `data_type`. `msg` and `data` are each a `(ptr, len)`
+/// pair.
+pub fn trace_call(data_type: TraceDataType, msg: &str, data: &str) -> String {
+    format!(
+        "(call $trace {msg} (i32.const {code}) {data})",
+        code = data_type.code()
+    )
+}
+
+/// [`trace_call`] as a whole module body: the call, then the constant that stands
+/// in for the status it does not return.
+pub fn traced(data_type: TraceDataType, msg: &str, data: &str) -> String {
+    format!(
+        "{call}\n    (i32.const {COMPLETED})",
+        call = trace_call(data_type, msg, data)
+    )
+}
+
+/// A module of `parts`, wrapping `body` in an exported `finish` returning `i32`.
+pub fn module(parts: &[&str], body: &str) -> String {
+    format!(
+        "(module {parts}\n  (func (export \"{ENTRY}\") (result i32)\n    {body}))",
+        parts = parts.join("\n  ")
+    )
+}
+
+// ---------------------------------------------------------------------------
+// Running
+//
+// The tests write their modules as text and assemble them here: the VM takes
+// binaries only, so the crate builds `wasmi` without its `wat` feature.
+// ---------------------------------------------------------------------------
+
+/// Assembles a text-format module into the binary the VM takes.
+///
+/// Panics rather than returning an error: text that will not assemble is a
+/// mistake in the test, not a case under test.
+pub fn assemble(wat: &str) -> Vec<u8> {
+    wat::parse_str(wat)
+        .unwrap_or_else(|e| panic!("this test's module does not assemble: {e}\n{wat}"))
+}
+
+/// Runs `wat`'s `finish` against `host` with gas to spare.
+pub fn run(wat: &str, host: &FakeHost) -> Result<RunOutcome, RunFailure> {
+    run_with_gas(wat, PLENTY_OF_GAS, host)
+}
+
+/// Runs `wat`'s `finish` against `host` with exactly `gas` to spend.
+pub fn run_with_gas(wat: &str, gas: u64, host: &FakeHost) -> Result<RunOutcome, RunFailure> {
+    xrpl_wasm_vm::run(&assemble(wat), gas, host, ENTRY)
+}
+
+/// Runs the export named `entry` rather than `finish`.
+pub fn run_entry(wat: &str, host: &FakeHost, entry: &str) -> Result<RunOutcome, RunFailure> {
+    xrpl_wasm_vm::run(&assemble(wat), PLENTY_OF_GAS, host, entry)
+}
+
+/// The value `finish` returned, for a run expected to complete: the host call's
+/// status, so a byte count on success or a negative [`HostError`] code.
+pub fn status(wat: &str, host: &FakeHost) -> i32 {
+    run(wat, host)
+        .unwrap_or_else(|e| panic!("expected the module to run, but: {e}\n{wat}"))
+        .result
+}
+
+/// The wire code a `HostError` reaches the guest as, for readable assertions.
+pub fn code(error: HostError) -> i32 {
+    error.code()
+}
+
+/// The failure from a run that was expected not to complete.
+pub fn failure(wat: &str, host: &FakeHost) -> RunFailure {
+    match run(wat, host) {
+        Err(failure) => failure,
+        Ok(outcome) => panic!(
+            "expected a failure, but the module returned {}",
+            outcome.result
+        ),
+    }
+}
diff --git a/crates/xrpl-wasm-vm/tests/vm_limits.rs b/crates/xrpl-wasm-vm/tests/vm_limits.rs
new file mode 100644
index 00000000000..4fa60e80148
--- /dev/null
+++ b/crates/xrpl-wasm-vm/tests/vm_limits.rs
@@ -0,0 +1,580 @@
+//! What the engine refuses outright: modules it will not compile, will not
+//! instantiate, or cannot find an entry point in — plus the linear-memory cap.
+//!
+//! These are the sandbox's outer wall. Everything here fails the run rather than
+//! returning a code to the guest, so each test reads the failure's message.
+
+mod support;
+
+use support::{
+    FakeHost, ONE_PAGE, PLENTY_OF_GAS, failure, import, module, run, run_entry, run_with_gas,
+};
+use xrpl_wasm_vm::{MAX_MEMORY_PAGES, RunError};
+
+/// Assert which stage a run failed at, because the caller maps the stages to
+/// different outcomes. A stage is one `RunError` variant, so the expectation is a
+/// pattern; the failure comes back out for the tests that also read its message.
+macro_rules! assert_stage {
+    ($failure:expr, $stage:pat) => {{
+        let failure = $failure;
+        assert!(
+            matches!(failure.error, $stage),
+            concat!("expected a ", stringify!($stage), " failure, got: {}"),
+            failure
+        );
+        failure
+    }};
+}
+
+// ---------------------------------------------------------------------------
+// Linear memory
+// ---------------------------------------------------------------------------
+
+/// A module declaring more than the cap fails to instantiate — the limit applies
+/// to the initial memory, not only to growth.
+#[test]
+fn an_initial_memory_past_the_cap_is_refused() {
+    let host = FakeHost::new();
+
+    let wat = module(
+        &[&format!(
+            r#"(memory (export "memory") {})"#,
+            MAX_MEMORY_PAGES + 1
+        )],
+        "(i32.const 0)",
+    );
+    assert_stage!(failure(&wat, &host), RunError::Instantiate(_));
+}
+
+/// The cap itself is allowed.
+#[test]
+fn an_initial_memory_at_the_cap_is_allowed() {
+    let host = FakeHost::new();
+
+    let wat = module(
+        &[&format!(r#"(memory (export "memory") {MAX_MEMORY_PAGES})"#)],
+        "(i32.const 0)",
+    );
+    assert_eq!(run(&wat, &host).expect("should run").result, 0);
+}
+
+/// Growth up to the cap succeeds; growth past it traps rather than answering -1 as
+/// `memory.grow` otherwise would, because the engine's limiter sets
+/// `trap_on_grow_failure(true)`.
+#[test]
+fn growth_stops_at_the_cap() {
+    let host = FakeHost::new();
+
+    let wat = module(
+        &[ONE_PAGE],
+        &format!("(memory.grow (i32.const {}))", MAX_MEMORY_PAGES - 1),
+    );
+    assert_eq!(
+        run(&wat, &host).expect("should run").result,
+        1,
+        "growing to exactly the cap answers the previous size"
+    );
+
+    let wat = module(
+        &[ONE_PAGE],
+        &format!("(memory.grow (i32.const {MAX_MEMORY_PAGES}))"),
+    );
+    assert_stage!(failure(&wat, &host), RunError::Trap(_));
+}
+
+/// A module may declare a maximum above the cap: the cap is enforced on the initial
+/// memory and on growth, not on the memory type's declared bound.
+#[test]
+fn a_declared_maximum_past_the_cap_is_allowed_but_unreachable() {
+    let host = FakeHost::new();
+    let memory = format!(r#"(memory (export "memory") 1 {})"#, MAX_MEMORY_PAGES + 1);
+
+    let wat = module(&[&memory], "(i32.const 0)");
+    assert_eq!(run(&wat, &host).expect("should run").result, 0);
+
+    let wat = module(
+        &[&memory],
+        &format!("(memory.grow (i32.const {MAX_MEMORY_PAGES}))"),
+    );
+    assert_stage!(failure(&wat, &host), RunError::Trap(_));
+}
+
+// ---------------------------------------------------------------------------
+// Engine configuration
+// ---------------------------------------------------------------------------
+
+/// One row per feature `build_wasm_engine` turns off: the smallest module that uses
+/// it, and the fragment of wasmi's refusal that names the feature. A row declaring
+/// its own memory omits [`ONE_PAGE`], or it is refused for having two memories
+/// instead.
+fn disabled_features() -> Vec<(&'static str, Vec<&'static str>, &'static str, &'static str)> {
+    vec![
+        (
+            "wasm_multi_value",
+            vec![
+                ONE_PAGE,
+                "(func $two (result i32 i32) (i32.const 1) (i32.const 2))",
+            ],
+            "(call $two) (drop) (drop) (i32.const 0)",
+            "multi-value",
+        ),
+        (
+            "wasm_sign_extension",
+            vec![ONE_PAGE],
+            "(i32.extend8_s (i32.const 1))",
+            "sign extension",
+        ),
+        (
+            "wasm_bulk_memory",
+            vec![ONE_PAGE],
+            "(memory.fill (i32.const 0) (i32.const 0) (i32.const 1)) (i32.const 0)",
+            "bulk memory",
+        ),
+        (
+            "wasm_reference_types",
+            vec![ONE_PAGE, "(table 1 externref)"],
+            "(i32.const 0)",
+            "reference types",
+        ),
+        // The proposal covers mutable globals crossing the module boundary; an
+        // internal one is core wasm and stays allowed — see the test below.
+        (
+            "wasm_mutable_global",
+            vec![ONE_PAGE, r#"(global (export "g") (mut i32) (i32.const 0))"#],
+            "(i32.const 0)",
+            "mutable global",
+        ),
+        (
+            "wasm_tail_call",
+            vec![ONE_PAGE, "(func $f (result i32) (i32.const 0))"],
+            "(return_call $f)",
+            "tail call",
+        ),
+        // Arithmetic in a constant initialiser. wasmi names the operator rather
+        // than the proposal here.
+        (
+            "wasm_extended_const",
+            vec![
+                ONE_PAGE,
+                "(global $g i32 (i32.add (i32.const 1) (i32.const 2)))",
+            ],
+            "(global.get $g)",
+            "non-constant operator",
+        ),
+        (
+            "wasm_multi_memory",
+            vec![ONE_PAGE, "(memory 1)"],
+            "(i32.const 0)",
+            "multiple memories",
+        ),
+        (
+            "wasm_memory64",
+            vec![r#"(memory (export "memory") i64 1)"#],
+            "(i32.const 0)",
+            "memory64",
+        ),
+        (
+            "wasm_custom_page_sizes",
+            vec![r#"(memory (export "memory") 1 (pagesize 1))"#],
+            "(i32.const 0)",
+            "custom page sizes",
+        ),
+        (
+            "wasm_wide_arithmetic",
+            vec![ONE_PAGE],
+            "(drop (i64.add128 (i64.const 1) (i64.const 2) (i64.const 3) (i64.const 4)))
+             (i32.const 0)",
+            "wide arithmetic",
+        ),
+        // Determinism across nodes is the reason floats are off.
+        (
+            "floats",
+            vec![ONE_PAGE],
+            "(drop (f64.add (f64.const 1) (f64.const 2))) (i32.const 0)",
+            "floating-point",
+        ),
+    ]
+}
+
+/// Every feature the engine disables is refused, and refused for that reason.
+///
+/// `wasm_custom_page_sizes` and `wasm_wide_arithmetic` are off by default in wasmi
+/// 1.1 (`engine/config.rs:72,74`), so their rows guard against wasmi changing that
+/// default rather than against our own config.
+#[test]
+fn every_disabled_feature_is_refused_by_name() {
+    let host = FakeHost::new();
+
+    for (knob, parts, body, expected) in disabled_features() {
+        let wat = module(&parts, body);
+        let failure = assert_stage!(failure(&wat, &host), RunError::Compile(_)).to_string();
+
+        assert!(
+            failure.contains(expected),
+            "{knob}: expected a refusal mentioning {expected:?}, got: {failure}"
+        );
+    }
+}
+
+/// The three knobs [`every_disabled_feature_is_refused_by_name`] cannot cover. The
+/// engine is a process-wide `LazyLock`, so a test observes the one configuration we
+/// build: a knob masked by another, or with no caller-visible effect, has no
+/// distinguishing module.
+#[test]
+fn the_knobs_without_a_module_of_their_own() {
+    let host = FakeHost::new();
+
+    // `wasm_saturating_float_to_int(false)`: every saturating conversion takes a
+    // float operand, so `floats(false)` refuses it first, as the message shows.
+    let wat = module(&[ONE_PAGE], "(i32.trunc_sat_f32_s (f32.const 1))");
+    let refusal = failure(&wat, &host).to_string();
+    assert!(refusal.contains("floating-point"), "{refusal}");
+    assert!(!refusal.contains("saturating"), "{refusal}");
+
+    // `ignore_custom_sections(true)`: governs whether wasmi retains custom
+    // sections, not accept/reject, so this pins only that one is harmless.
+    let wat = module(
+        &[ONE_PAGE, r#"(@custom "note" "ignored")"#],
+        "(i32.const 0)",
+    );
+    assert_eq!(run(&wat, &host).expect("should run").result, 0);
+
+    // `consume_fuel(true)`: with it off, `Store::set_fuel` fails and `run` returns
+    // before instantiating, so every test in the suite fails.
+    let wat = module(&[ONE_PAGE], "(i32.const 0)");
+    assert!(run(&wat, &host).expect("should run").fuel_used > 0);
+}
+
+/// A mutable global the module keeps to itself is core wasm, so the disabled
+/// proposal does not reach it: a guest can still have mutable state.
+#[test]
+fn an_internal_mutable_global_is_still_allowed() {
+    let host = FakeHost::new();
+
+    let wat = module(
+        &[ONE_PAGE, "(global $g (mut i32) (i32.const 0))"],
+        "(global.set $g (i32.const 7)) (global.get $g)",
+    );
+    assert_eq!(run(&wat, &host).expect("should run").result, 7);
+}
+
+/// Bytes that are not a wasm module at all.
+#[test]
+fn garbage_does_not_compile() {
+    let host = FakeHost::new();
+
+    for bytes in [b"".as_slice(), b"not wasm", &[0x00, 0x61, 0x73, 0x6d]] {
+        let failure = xrpl_wasm_vm::run(bytes, PLENTY_OF_GAS, &host, support::ENTRY)
+            .expect_err("garbage must not compile");
+        assert_stage!(failure, RunError::Compile(_));
+    }
+}
+
+/// The VM takes wasm binaries, and text is not one. wasmi's `wat` feature is on by
+/// default and would have `Module::new` assemble text too, so the crate builds
+/// wasmi without it; turning it back on would make this transaction blob valid.
+#[test]
+fn the_vm_refuses_a_text_format_module() {
+    let host = FakeHost::new();
+    let text = module(&[ONE_PAGE], "(i32.const 0)");
+
+    let failure = xrpl_wasm_vm::run(text.as_bytes(), PLENTY_OF_GAS, &host, support::ENTRY)
+        .expect_err("text must not compile as a module");
+    assert_stage!(failure, RunError::Compile(_));
+
+    // The same module, assembled first, runs: the text is sound and only the
+    // format was refused.
+    assert_eq!(run(&text, &host).expect("should run").result, 0);
+}
+
+// ---------------------------------------------------------------------------
+// Imports
+// ---------------------------------------------------------------------------
+
+/// A module may import fewer host functions than are registered, but not more:
+/// an import the linker does not define fails instantiation.
+#[test]
+fn an_unknown_import_fails_instantiation() {
+    let host = FakeHost::new();
+
+    let wat = module(
+        &[
+            r#"(import "host_lib" "no_such_function" (func $f (param i32) (result i32)))"#,
+            ONE_PAGE,
+        ],
+        "(call $f (i32.const 0))",
+    );
+    assert_stage!(failure(&wat, &host), RunError::Instantiate(_));
+}
+
+/// Host functions are registered under one module name — `host_lib`, the name the
+/// guest SDK and this repo's fixtures import from — and a guest naming a different
+/// one does not link. `env` is in the list because that is what plain clang emits.
+#[test]
+fn the_import_module_name_must_match() {
+    let host = FakeHost::new();
+
+    for module_name in ["host", "env", ""] {
+        let wat = module(
+            &[
+                &format!(
+                    r#"(import "{module_name}" "ldgr_index" (func $f (param i32 i32) (result i32)))"#
+                ),
+                ONE_PAGE,
+            ],
+            "(call $f (i32.const 0) (i32.const 4))",
+        );
+        assert_stage!(failure(&wat, &host), RunError::Instantiate(_));
+    }
+}
+
+/// An import spelled with the wrong signature does not link even under the right
+/// name, which is what makes the registered signatures load-bearing.
+#[test]
+fn an_import_with_the_wrong_signature_fails_instantiation() {
+    let host = FakeHost::new();
+
+    for signature in [
+        "(param i32) (result i32)",         // too few parameters
+        "(param i32 i32 i32) (result i32)", // too many
+        "(param i64 i64) (result i32)",     // wrong parameter types
+        "(param i32 i32) (result i64)",     // wrong result type
+        "(param i32 i32)",                  // no result
+    ] {
+        let wat = module(
+            &[
+                &format!(r#"(import "host_lib" "ldgr_index" (func $f {signature}))"#),
+                ONE_PAGE,
+            ],
+            "(i32.const 0)",
+        );
+        assert_stage!(failure(&wat, &host), RunError::Instantiate(_));
+    }
+}
+
+/// A module that imports a host function it never calls still has to link.
+#[test]
+fn an_unused_import_is_still_linked() {
+    let host = FakeHost::new();
+
+    let wat = module(
+        &[import::LDGR_INDEX, import::TRACE, ONE_PAGE],
+        "(i32.const 0)",
+    );
+    assert_eq!(run(&wat, &host).expect("should run").result, 0);
+}
+
+// ---------------------------------------------------------------------------
+// The start section
+// ---------------------------------------------------------------------------
+
+/// A start section runs guest code during instantiation, before the entry point
+/// is even looked up, and `set_fuel` and the memory limiter are both installed by
+/// then — so it is metered like any other guest code, and a run it stops is
+/// charged for what it burned.
+///
+/// Reported as a **trap**, not as a module that would not instantiate: a trap is the
+/// guest's fault wherever it happens, and the stage a run stopped at is not what the
+/// caller maps. Filing it under the stage would put a contract's own defect among the
+/// faults a caller treats as the node's, and charge nothing for the instructions the
+/// contract burned reaching it.
+#[test]
+fn a_trapping_start_section_is_a_guest_trap_and_is_charged() {
+    let host = FakeHost::new();
+
+    let wat = format!(
+        r#"(module {ONE_PAGE}
+             (func $init (unreachable))
+             (start $init)
+             (func (export "finish") (result i32) (i32.const 0)))"#
+    );
+    let failure = assert_stage!(
+        run_with_gas(&wat, PLENTY_OF_GAS, &host)
+            .expect_err("a start section that traps must not complete the run"),
+        RunError::Trap(_)
+    );
+    assert!(
+        failure.fuel_used > 0,
+        "the start section's instructions are metered: {failure}"
+    );
+}
+
+/// What `RunError::Instantiate` is left to mean: a module the linker or the store
+/// would not accept, rather than one whose guest code failed. Its two shapes, so the
+/// variant is not left standing for nothing.
+#[test]
+fn instantiation_failure_is_a_module_the_engine_will_not_accept() {
+    let host = FakeHost::new();
+
+    // The linker defines no such import.
+    let wat = module(
+        &[
+            r#"(import "host_lib" "no_such_function" (func $f (result i32)))"#,
+            ONE_PAGE,
+        ],
+        "(call $f)",
+    );
+    assert_stage!(failure(&wat, &host), RunError::Instantiate(_));
+
+    // The store's limiter will not grant the memory, and does not trap to say so.
+    let wat = module(
+        &[&format!("(memory {})", MAX_MEMORY_PAGES + 1)],
+        "(i32.const 0)",
+    );
+    assert_stage!(failure(&wat, &host), RunError::Instantiate(_));
+}
+
+/// A start section that runs out of gas is reported as out of gas, not as a module
+/// that would not instantiate. The stage a run stopped at is not what the caller
+/// maps — the reason is — and gas exhaustion is one outcome wherever the guest
+/// reaches it.
+#[test]
+fn a_start_section_that_exhausts_gas_is_out_of_gas_not_an_instantiation_failure() {
+    const GAS: u64 = 10_000;
+
+    let host = FakeHost::new();
+    let wat = format!(
+        r#"(module {ONE_PAGE}
+             (func $init (loop $l (br $l)))
+             (start $init)
+             (func (export "finish") (result i32) (i32.const 0)))"#
+    );
+
+    let failure = assert_stage!(
+        run_with_gas(&wat, GAS, &host).expect_err("an endless start section must not instantiate"),
+        RunError::OutOfGas
+    );
+    assert_eq!(
+        failure.fuel_used, GAS,
+        "a runaway start section burns the whole limit"
+    );
+}
+
+/// A start section cannot make a host call that needs guest memory, even in a
+/// module that exports one: the memory is resolved from the *instance's* exports,
+/// and instantiation is what produces the instance, so a call made while it is
+/// still running has no memory to work in and ends the run.
+///
+/// Not a choice: `Module::instantiate` is `pub(crate)` in wasmi, so instantiation
+/// cannot be split from the start section to resolve the memory in between.
+#[test]
+fn a_start_section_cannot_make_a_host_call() {
+    let host = FakeHost::new();
+
+    let wat = format!(
+        r#"(module {ldgr_index} {ONE_PAGE}
+             (func $init (drop (call $ldgr_index (i32.const 0) (i32.const 4))))
+             (start $init)
+             (func (export "finish") (result i32) (i32.const 0)))"#,
+        ldgr_index = import::LDGR_INDEX
+    );
+
+    let failure = assert_stage!(
+        run_with_gas(&wat, PLENTY_OF_GAS, &host)
+            .expect_err("a host call from a start section must not be served"),
+        RunError::NoMemory
+    );
+    assert!(
+        failure.fuel_used > 0,
+        "the start section is metered up to the refused call: {failure}"
+    );
+}
+
+// ---------------------------------------------------------------------------
+// The entry point
+// ---------------------------------------------------------------------------
+
+#[test]
+fn a_missing_entry_point_fails() {
+    let host = FakeHost::new();
+
+    let wat = r#"(module (memory (export "memory") 1) (func (export "other") (result i32) (i32.const 0)))"#;
+    let failure = assert_stage!(
+        run_with_gas(wat, PLENTY_OF_GAS, &host)
+            .expect_err("a module without the entry point must not run"),
+        RunError::EntryPoint(_)
+    );
+    assert!(
+        failure.to_string().contains("no entry point 'finish'"),
+        "{failure}"
+    );
+}
+
+/// The entry point is looked up by the name the caller asks for.
+#[test]
+fn the_entry_point_is_the_name_the_caller_gives() {
+    let host = FakeHost::new();
+
+    let wat = r#"(module (memory (export "memory") 1) (func (export "other") (result i32) (i32.const 9)))"#;
+    let outcome = run_entry(wat, &host, "other").expect("should run");
+    assert_eq!(outcome.result, 9);
+}
+
+/// The entry point must take nothing and return an `i32`. A module that exports the
+/// name with another signature is told so, rather than being told the export is
+/// missing: wasmi answers both cases with one error, and "no entry point" would send
+/// a contract author looking for a function they already have.
+#[test]
+fn an_entry_point_of_the_wrong_type_fails() {
+    let host = FakeHost::new();
+
+    for signature in ["(result i64)", "(param i32) (result i32)", ""] {
+        let body = if signature.contains("result i64") {
+            "(i64.const 0)"
+        } else if signature.is_empty() {
+            "(nop)"
+        } else {
+            "(i32.const 0)"
+        };
+        let wat = format!(
+            r#"(module (memory (export "memory") 1) (func (export "finish") {signature} {body}))"#
+        );
+        let failure = assert_stage!(
+            run_with_gas(&wat, PLENTY_OF_GAS, &host)
+                .expect_err("a wrongly-typed entry point must not run"),
+            RunError::EntryPoint(_)
+        )
+        .to_string();
+        assert!(
+            failure.contains("entry point 'finish' has the wrong signature"),
+            "{signature}: {failure}"
+        );
+        assert!(
+            !failure.contains("no entry point"),
+            "a present export must not be reported as absent — {signature}: {failure}"
+        );
+    }
+}
+
+/// An export of the entry point's name that is not a function at all is a third
+/// case, and named as such: nothing is missing and no signature is wrong.
+#[test]
+fn an_entry_point_that_is_not_a_function_fails() {
+    let host = FakeHost::new();
+
+    let wat =
+        r#"(module (memory (export "memory") 1) (global (export "finish") i32 (i32.const 0)))"#;
+    let failure = assert_stage!(
+        run_with_gas(wat, PLENTY_OF_GAS, &host).expect_err("a non-function export must not run"),
+        RunError::EntryPoint(_)
+    )
+    .to_string();
+    assert!(
+        failure.contains("export 'finish' is not a function"),
+        "{failure}"
+    );
+}
+
+/// A guest that traps fails the run rather than returning a value.
+#[test]
+fn a_trapping_guest_fails_the_run() {
+    let host = FakeHost::new();
+
+    let wat = module(&[ONE_PAGE], "(unreachable)");
+    assert_stage!(failure(&wat, &host), RunError::Trap(_));
+
+    // An out-of-bounds guest access is a trap too, caught by the engine rather
+    // than anything the host is asked about.
+    let wat = module(&[ONE_PAGE], "(i32.load (i32.const 100000))");
+    assert_stage!(failure(&wat, &host), RunError::Trap(_));
+}
diff --git a/include/xrpl/tx/wasm/HostContext.h b/include/xrpl/tx/wasm/HostContext.h
new file mode 100644
index 00000000000..7ba70e0b6e7
--- /dev/null
+++ b/include/xrpl/tx/wasm/HostContext.h
@@ -0,0 +1,74 @@
+#pragma once
+
+#include <rust/cxx.h>
+
+#include <cstdint>
+
+namespace xrpl {
+// `xrpl::HostFunctions` is forward-declared rather than included: this header is
+// `include!()`d by the cxxbridge-generated translation unit, whose target gets only the
+// project's `include/` directory - not the Boost paths that HostFunc.h -> Slice.h ->
+// strHex.h transitively need. A reference member and declarations alone do not require a
+// complete type; HostContext.cpp, compiled into libxrpl, includes the real header.
+class HostFunctions;
+
+// Defined by the cxx bridge, which emits it into `xrpl_wasm_vm_ffi_cxxbridge/lib.h` from the
+// declaration in `crates/xrpl-wasm-vm-ffi` - so the data types and their wire values are
+// written once, in Rust, rather than kept in step with a copy here.
+//
+// Forward-declared for the reason `HostFunctions` above is: that generated header includes
+// this one, so naming its definition here would be circular. A scoped enum with a fixed
+// underlying type needs no definition to appear in a signature; `HostContext.cpp` includes
+// the generated header for the `switch`.
+enum class TraceDataType : std::int32_t;
+
+// The host handed to the Rust wasm engine: one method per entry in the wasm host ABI,
+// each forwarding to `xrpl::HostFunctions` - the single source of truth for ledger
+// access - and lowering its typed `std::expected` result onto the ABI's wire form.
+//
+// Every method is `noexcept`, and every body catches everything: a C++ exception
+// unwinding into the Rust frames that called it would be undefined behaviour, so a
+// failure leaves here as -1, which the engine reads as a fatal error and reports as
+// `tecINTERNAL`.
+//
+// Not an owner: it borrows `hf` for the length of one run. Declared `struct` because the
+// Rust side only ever sees an opaque pointer.
+class HostContext
+{
+    // Non-const so a host function that mutates (`cacheLedgerObj`, `updateData`) can be
+    // reached from the `const` methods below: constness of the reference is not
+    // constness of the referent.
+    HostFunctions& hostFunctions_;
+
+public:
+    HostContext(HostFunctions& hostFunctions);
+
+    // A byte-producing call is handed `out` - a slice aliasing either guest linear
+    // memory or the engine's output buffer - writes the value only if the whole of it
+    // fits, and returns the value's *true* length, which may exceed `out`. That is how a
+    // guest learns the size to ask for, and it is why these methods never need to know
+    // the guest's capacity: the engine owns the buffer-fit, field-cap and transfer-budget
+    // rules and derives all three from the length returned here.
+    //
+    // A negative return is a `HostFunctionError` code.
+    [[nodiscard]] std::int32_t
+    getLedgerSqn(rust::Slice<std::uint8_t> out) const noexcept;
+
+    [[nodiscard]] std::int32_t
+    getCurrentLedgerObjField(std::int32_t field, rust::Slice<std::uint8_t> out) const noexcept;
+
+    [[nodiscard]] std::int32_t
+    sha512Half(rust::Slice<std::uint8_t const> data, rust::Slice<std::uint8_t> out) const noexcept;
+
+    // Renders `data` as `dataType` says, and hands the text to `HostFunctions::trace`, which
+    // is what puts it in this node's log.
+    //
+    // The one call that answers nothing: the guest's wasm function has no result, and this
+    // node's own log is the only thing a trace touches, so a buffer that does not hold what
+    // it claims is logged here and dropped rather than reported to a contract.
+    void
+    trace(rust::Str msg, rust::Slice<std::uint8_t const> data, TraceDataType dataType)
+        const noexcept;
+};
+
+}  // namespace xrpl
diff --git a/include/xrpl/tx/wasm/HostFunc.h b/include/xrpl/tx/wasm/HostFunc.h
index 96953fbf90c..ae0adcd9be4 100644
--- a/include/xrpl/tx/wasm/HostFunc.h
+++ b/include/xrpl/tx/wasm/HostFunc.h
@@ -2,7 +2,6 @@
 
 #include <xrpl/basics/Slice.h>
 #include <xrpl/basics/base_uint.h>
-#include <xrpl/basics/contract.h>
 #include <xrpl/beast/utility/Journal.h>
 #include <xrpl/protocol/AccountID.h>
 #include <xrpl/protocol/Asset.h>
@@ -12,9 +11,6 @@
 
 #include <cstdint>
 #include <expected>
-#include <functional>
-#include <optional>
-#include <stdexcept>
 #include <string>
 #include <string_view>
 
@@ -73,7 +69,6 @@ floatPowerImpl(Slice const& x, int32_t n, int32_t mode);
 class HostFunctions
 {
 protected:
-    RTOptRef rt_;
     beast::Journal j_;
 
 public:
@@ -81,26 +76,6 @@ class HostFunctions
     {
     }
 
-    void
-    setRT(WasmRuntimeWrapper& rt)
-    {
-        rt_ = rt;
-    }
-
-    void
-    resetRT()
-    {
-        rt_ = std::nullopt;
-    }
-
-    [[nodiscard]] WasmRuntimeWrapper&
-    getRT() const
-    {
-        if (!rt_)
-            Throw<std::logic_error>("Wasm runtime not set");
-        return rt_->get();
-    }
-
     [[nodiscard]] beast::Journal
     getJournal() const
     {
@@ -495,6 +470,4 @@ class HostFunctions
     // LCOV_EXCL_STOP
 };
 
-using HFRef = std::reference_wrapper<HostFunctions>;
-
 }  // namespace xrpl
diff --git a/include/xrpl/tx/wasm/HostFuncWrapper.h b/include/xrpl/tx/wasm/HostFuncWrapper.h
deleted file mode 100644
index 4884c750f16..00000000000
--- a/include/xrpl/tx/wasm/HostFuncWrapper.h
+++ /dev/null
@@ -1,244 +0,0 @@
-#pragma once
-
-#include <xrpl/tx/wasm/HostFunc.h>
-
-#include <wasm.h>
-
-#include <cstdint>
-
-namespace xrpl {
-
-#define WASM_CB_PARAMS_LIST void *env, wasm_val_vec_t const *params, wasm_val_vec_t *results
-#define WASM_SECONDARY_CB_PARAMS_LIST \
-    HostFunctions &hf, wasm_val_vec_t const *params, wasm_val_vec_t *results
-
-wasm_trap_t* HostFuncMain_wrap(WASM_CB_PARAMS_LIST);
-
-using getLedgerSqn_proto = int32_t(uint8_t*, int32_t);
-wasm_trap_t* getLedgerSqn_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using getParentLedgerTime_proto = int32_t(uint8_t*, int32_t);
-wasm_trap_t* getParentLedgerTime_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using getParentLedgerHash_proto = int32_t(uint8_t*, int32_t);
-wasm_trap_t* getParentLedgerHash_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using getBaseFee_proto = int32_t(uint8_t*, int32_t);
-wasm_trap_t* getBaseFee_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using isAmendmentEnabled_proto = int32_t(uint8_t const*, int32_t);
-wasm_trap_t* isAmendmentEnabled_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using cacheLedgerObj_proto = int32_t(uint8_t const*, int32_t, int32_t);
-wasm_trap_t* cacheLedgerObj_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using getTxField_proto = int32_t(int32_t, uint8_t*, int32_t);
-wasm_trap_t* getTxField_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using getCurrentLedgerObjField_proto = int32_t(int32_t, uint8_t*, int32_t);
-wasm_trap_t* getCurrentLedgerObjField_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using getLedgerObjField_proto = int32_t(int32_t, int32_t, uint8_t*, int32_t);
-wasm_trap_t* getLedgerObjField_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using getTxNestedField_proto = int32_t(uint8_t const*, int32_t, uint8_t*, int32_t);
-wasm_trap_t* getTxNestedField_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using getCurrentLedgerObjNestedField_proto = int32_t(uint8_t const*, int32_t, uint8_t*, int32_t);
-wasm_trap_t* getCurrentLedgerObjNestedField_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using getLedgerObjNestedField_proto = int32_t(int32_t, uint8_t const*, int32_t, uint8_t*, int32_t);
-wasm_trap_t* getLedgerObjNestedField_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using getTxArrayLen_proto = int32_t(int32_t);
-wasm_trap_t* getTxArrayLen_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using getCurrentLedgerObjArrayLen_proto = int32_t(int32_t);
-wasm_trap_t* getCurrentLedgerObjArrayLen_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using getLedgerObjArrayLen_proto = int32_t(int32_t, int32_t);
-wasm_trap_t* getLedgerObjArrayLen_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using getTxNestedArrayLen_proto = int32_t(uint8_t const*, int32_t);
-wasm_trap_t* getTxNestedArrayLen_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using getCurrentLedgerObjNestedArrayLen_proto = int32_t(uint8_t const*, int32_t);
-wasm_trap_t* getCurrentLedgerObjNestedArrayLen_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using getLedgerObjNestedArrayLen_proto = int32_t(int32_t, uint8_t const*, int32_t);
-wasm_trap_t* getLedgerObjNestedArrayLen_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using updateData_proto = int32_t(uint8_t const*, int32_t);
-wasm_trap_t* updateData_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using checkSignature_proto =
-    int32_t(uint8_t const*, int32_t, uint8_t const*, int32_t, uint8_t const*, int32_t);
-wasm_trap_t* checkSignature_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using computeSha512HalfHash_proto = int32_t(uint8_t const*, int32_t, uint8_t*, int32_t);
-wasm_trap_t* computeSha512HalfHash_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using accountKeylet_proto = int32_t(uint8_t const*, int32_t, uint8_t*, int32_t);
-wasm_trap_t* accountKeylet_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using ammKeylet_proto =
-    int32_t(uint8_t const*, int32_t, uint8_t const*, int32_t, uint8_t*, int32_t);
-wasm_trap_t* ammKeylet_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using checkKeylet_proto =
-    int32_t(uint8_t const*, int32_t, uint8_t const*, int32_t, uint8_t*, int32_t);
-wasm_trap_t* checkKeylet_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using credentialKeylet_proto = int32_t(
-    uint8_t const*,
-    int32_t,
-    uint8_t const*,
-    int32_t,
-    uint8_t const*,
-    int32_t,
-    uint8_t*,
-    int32_t);
-wasm_trap_t* credentialKeylet_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using delegateKeylet_proto =
-    int32_t(uint8_t const*, int32_t, uint8_t const*, int32_t, uint8_t*, int32_t);
-wasm_trap_t* delegateKeylet_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using depositPreauthKeylet_proto =
-    int32_t(uint8_t const*, int32_t, uint8_t const*, int32_t, uint8_t*, int32_t);
-wasm_trap_t* depositPreauthKeylet_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using didKeylet_proto = int32_t(uint8_t const*, int32_t, uint8_t*, int32_t);
-wasm_trap_t* didKeylet_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using escrowKeylet_proto =
-    int32_t(uint8_t const*, int32_t, uint8_t const*, int32_t, uint8_t*, int32_t);
-wasm_trap_t* escrowKeylet_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using trustLineKeylet_proto = int32_t(
-    uint8_t const*,
-    int32_t,
-    uint8_t const*,
-    int32_t,
-    uint8_t const*,
-    int32_t,
-    uint8_t*,
-    int32_t);
-wasm_trap_t* trustLineKeylet_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using mptokenIssuanceKeylet_proto =
-    int32_t(uint8_t const*, int32_t, uint8_t const*, int32_t, uint8_t*, int32_t);
-wasm_trap_t* mptokenIssuanceKeylet_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using mptokenKeylet_proto =
-    int32_t(uint8_t const*, int32_t, uint8_t const*, int32_t, uint8_t*, int32_t);
-wasm_trap_t* mptokenKeylet_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using nftokenOfferKeylet_proto =
-    int32_t(uint8_t const*, int32_t, uint8_t const*, int32_t, uint8_t*, int32_t);
-wasm_trap_t* nftokenOfferKeylet_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using offerKeylet_proto =
-    int32_t(uint8_t const*, int32_t, uint8_t const*, int32_t, uint8_t*, int32_t);
-wasm_trap_t* offerKeylet_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using oracleKeylet_proto =
-    int32_t(uint8_t const*, int32_t, uint8_t const*, int32_t, uint8_t*, int32_t);
-wasm_trap_t* oracleKeylet_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using paychannelKeylet_proto = int32_t(
-    uint8_t const*,
-    int32_t,
-    uint8_t const*,
-    int32_t,
-    uint8_t const*,
-    int32_t,
-    uint8_t*,
-    int32_t);
-wasm_trap_t* paychannelKeylet_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using permissionedDomainKeylet_proto =
-    int32_t(uint8_t const*, int32_t, uint8_t const*, int32_t, uint8_t*, int32_t);
-wasm_trap_t* permissionedDomainKeylet_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using signerListKeylet_proto = int32_t(uint8_t const*, int32_t, uint8_t*, int32_t);
-wasm_trap_t* signerListKeylet_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using ticketKeylet_proto =
-    int32_t(uint8_t const*, int32_t, uint8_t const*, int32_t, uint8_t*, int32_t);
-wasm_trap_t* ticketKeylet_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using vaultKeylet_proto =
-    int32_t(uint8_t const*, int32_t, uint8_t const*, int32_t, uint8_t*, int32_t);
-wasm_trap_t* vaultKeylet_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using getNFT_proto = int32_t(uint8_t const*, int32_t, uint8_t const*, int32_t, uint8_t*, int32_t);
-wasm_trap_t* getNFT_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using getNFTIssuer_proto = int32_t(uint8_t const*, int32_t, uint8_t*, int32_t);
-wasm_trap_t* getNFTIssuer_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using getNFTTaxon_proto = int32_t(uint8_t const*, int32_t, uint8_t*, int32_t);
-wasm_trap_t* getNFTTaxon_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using getNFTFlags_proto = int32_t(uint8_t const*, int32_t);
-wasm_trap_t* getNFTFlags_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using getNFTTransferFee_proto = int32_t(uint8_t const*, int32_t);
-wasm_trap_t* getNFTTransferFee_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using getNFTSequence_proto = int32_t(uint8_t const*, int32_t, uint8_t*, int32_t);
-wasm_trap_t* getNFTSequence_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-// trace(msg_ptr, msg_len, data_type, data_ptr, data_len); data_type is a
-// TraceDataType.
-using trace_proto = void(uint8_t const*, int32_t, int32_t, uint8_t const*, int32_t);
-wasm_trap_t* trace_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using floatFromInt_proto = int32_t(int64_t, uint8_t*, int32_t, int32_t);
-wasm_trap_t* floatFromInt_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using floatFromUint_proto = int32_t(uint8_t const*, int32_t, uint8_t*, int32_t, int32_t);
-wasm_trap_t* floatFromUint_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using floatFromSTAmount_proto = int32_t(uint8_t const*, int32_t, uint8_t*, int32_t, int32_t);
-wasm_trap_t* floatFromSTAmount_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using floatFromSTNumber_proto = int32_t(uint8_t const*, int32_t, uint8_t*, int32_t, int32_t);
-wasm_trap_t* floatFromSTNumber_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using floatToInt_proto = int32_t(uint8_t const*, int32_t, uint8_t*, int32_t, int32_t);
-wasm_trap_t* floatToInt_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using floatToMantExp_proto = int32_t(uint8_t const*, int32_t, uint8_t*, int32_t, uint8_t*, int32_t);
-wasm_trap_t* floatToMantExp_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using floatFromMantExp_proto = int32_t(int64_t, int32_t, uint8_t*, int32_t, int32_t);
-wasm_trap_t* floatFromMantExp_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using floatCompare_proto = int32_t(uint8_t const*, int32_t, uint8_t const*, int32_t);
-wasm_trap_t* floatCompare_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using floatAdd_proto =
-    int32_t(uint8_t const*, int32_t, uint8_t const*, int32_t, uint8_t*, int32_t, int32_t);
-wasm_trap_t* floatAdd_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using floatSubtract_proto =
-    int32_t(uint8_t const*, int32_t, uint8_t const*, int32_t, uint8_t*, int32_t, int32_t);
-wasm_trap_t* floatSubtract_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using floatMultiply_proto =
-    int32_t(uint8_t const*, int32_t, uint8_t const*, int32_t, uint8_t*, int32_t, int32_t);
-wasm_trap_t* floatMultiply_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using floatDivide_proto =
-    int32_t(uint8_t const*, int32_t, uint8_t const*, int32_t, uint8_t*, int32_t, int32_t);
-wasm_trap_t* floatDivide_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using floatRoot_proto = int32_t(uint8_t const*, int32_t, int32_t, uint8_t*, int32_t, int32_t);
-wasm_trap_t* floatRoot_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-using floatPower_proto = int32_t(uint8_t const*, int32_t, int32_t, uint8_t*, int32_t, int32_t);
-wasm_trap_t* floatPower_wrap(WASM_SECONDARY_CB_PARAMS_LIST);
-
-}  // namespace xrpl
diff --git a/include/xrpl/tx/wasm/README.md b/include/xrpl/tx/wasm/README.md
index 04958b663a6..7be22a6feb2 100644
--- a/include/xrpl/tx/wasm/README.md
+++ b/include/xrpl/tx/wasm/README.md
@@ -1,189 +1,40 @@
 # WASM Module for Programmable Escrows
 
-This module provides WebAssembly (WASM) execution capabilities for programmable
-escrows on the XRP Ledger. When an escrow is finished, the WASM code runs to
-determine whether the escrow conditions are met, enabling custom programmable
-logic for escrow release conditions.
-
-For the full specification, see
+WebAssembly execution for programmable escrows. When an escrow is finished, its contract
+runs to decide whether the release conditions are met. Specification:
 [XLS-0102: WASM VM](https://xls.xrpl.org/xls/XLS-0102-wasm-vm.html).
 
-## Architecture
-
-The module follows a layered architecture:
-
-```
-┌─────────────────────────────────────────────────────────────┐
-│                 WasmEngine (WasmVM.h)                       │
-│         runEscrowWasm(), preflightEscrowWasm()              │
-│              Host function registration                     │
-├─────────────────────────────────────────────────────────────┤
-│                 WasmiEngine (WasmiVM.h)                     │
-│            Low-level wasmi interpreter integration          │
-├─────────────────────────────────────────────────────────────┤
-│    HostFuncWrapper          │       HostFuncImpl            │
-│   C-style WASM bridges      │   C++ implementations         │
-├─────────────────────────────────────────────────────────────┤
-│                   HostFunc (Interface)                      │
-│            Abstract base class for host functions           │
-└─────────────────────────────────────────────────────────────┘
-```
-
-### Key Components
-
-- **`WasmVM.h` / `detail/WasmVM.cpp`** - High-level facade providing:
-  - `WasmEngine` singleton that wraps the underlying WASM interpreter
-  - `runEscrowWasm()` - Execute WASM code for escrow finish
-  - `preflightEscrowWasm()` - Validate WASM code during preflight
-  - `createWasmImport()` - Register all host functions
-
-- **`WasmiVM.h` / `detail/WasmiVM.cpp`** - Low-level integration with the
-  [wasmi](https://github.com/wasmi-labs/wasmi) WebAssembly interpreter:
-  - `WasmiEngine` - Manages WASM modules, instances, and execution
-  - Memory management and gas metering
-  - Function invocation and result handling
-
-- **`HostFunc.h`** - Abstract `HostFunctions` base class defining the interface
-  for all callable host functions. Each method returns
-  `std::expected<T, HostFunctionError>`.
-
-- **`HostFuncImpl.h` / `detail/HostFuncImpl*.cpp`** - Concrete
-  `WasmHostFunctionsImpl` class that implements host functions with access to
-  `ApplyContext` for ledger state queries. Implementation split across files:
-  - `HostFuncImpl.cpp` - Core utilities (updateData, checkSignature, etc.)
-  - `HostFuncImplFloat.cpp` - Float/number arithmetic operations
-  - `HostFuncImplGetter.cpp` - Field access (transaction, ledger objects)
-  - `HostFuncImplKeylet.cpp` - Keylet construction functions
-  - `HostFuncImplLedgerHeader.cpp` - Ledger header info access
-  - `HostFuncImplNFT.cpp` - NFT-related queries
-  - `HostFuncImplTrace.cpp` - Debugging/tracing functions
-
-- **`HostFuncWrapper.h` / `detail/HostFuncWrapper.cpp`** - C-style wrapper
-  functions that bridge WASM calls to C++ `HostFunctions` methods. Each host
-  function has:
-  - A `_proto` type alias defining the function signature
-  - A `_wrap` function that extracts parameters and calls the implementation
-
-- **`ParamsHelper.h`** - Utilities for WASM parameter handling:
-  - `WASM_IMPORT_FUNC` / `WASM_IMPORT_FUNC2` macros for registration
-  - `wasmParams()` helper for building parameter vectors
-  - Type conversion between WASM and C++ types
-
-## Host Functions
-
-Host functions allow WASM code to interact with the XRP Ledger. They are
-organized into categories:
-
-- **Ledger Information** - Access ledger sequence, timestamps, hashes, fees
-- **Transaction & Ledger Object Access** - Read fields from the transaction
-  and ledger objects (including the current escrow object)
-- **Keylet Construction** - Build keylets to look up various ledger object types
-- **Cryptography** - Signature verification and hashing
-- **Float Arithmetic** - Mathematical operations for amount calculations
-- **NFT Operations** - Query NFT properties
-- **Tracing/Debugging** - Log messages for debugging
-
-For the complete list of available host functions, their WASM names, and gas
-costs, see the [XLS-0102 specification](https://xls.xrpl.org/xls/XLS-0102-wasm-vm.html)
-or `detail/WasmVM.cpp` where they are registered via `WASM_IMPORT_FUNC2` macros.
-For method signatures, see `HostFunc.h`.
-
-## Gas Model
-
-Each host function has an associated gas cost. The gas cost is specified when
-registering the function in `detail/WasmVM.cpp`:
-
-```cpp
-WASM_IMPORT_FUNC2(i, getLedgerSqn, "get_ledger_sqn", hfs, 60);
-//                                                        ^^ gas cost
-```
-
-WASM execution is metered, and if the gas limit is exceeded, execution fails.
-
-## Entry Point
-
-The WASM module must export a function with the name defined by
-`escrowFunctionName` (currently `"escrow_finish"`). This function:
-
-- Takes no parameters (or parameters passed via host function calls)
-- Returns an `int32_t`:
-  - `1` (or positive): Escrow conditions are met, allow finish
-  - `0` (or negative): Escrow conditions are not met, reject finish
-
-## Adding a New Host Function
-
-To add a new host function, follow these steps:
-
-### 1. Add to HostFunc.h (Base Class)
-
-Add a virtual method declaration with a default implementation that returns an
-error:
-
-```cpp
-virtual std::expected<ReturnType, HostFunctionError>
-myNewFunction(ParamType1 param1, ParamType2 param2)
-{
-    return std::unexpected(HostFunctionError::INTERNAL);
-}
-```
-
-### 2. Add to HostFuncImpl.h (Declaration)
-
-Add the method override declaration in `WasmHostFunctionsImpl`:
-
-```cpp
-std::expected<ReturnType, HostFunctionError>
-myNewFunction(ParamType1 param1, ParamType2 param2) override;
-```
-
-### 3. Implement in detail/HostFuncImpl\*.cpp
-
-Add the implementation in the appropriate file:
-
-```cpp
-std::expected<ReturnType, HostFunctionError>
-WasmHostFunctionsImpl::myNewFunction(ParamType1 param1, ParamType2 param2)
-{
-    // Implementation using ctx (ApplyContext) for ledger access
-    return result;
-}
-```
-
-### 4. Add Wrapper to HostFuncWrapper.h
-
-Add the prototype and wrapper declaration:
-
-```cpp
-using myNewFunction_proto = int32_t(uint8_t const*, int32_t, ...);
-wasm_trap_t*
-myNewFunction_wrap(void* env, wasm_val_vec_t const* params, wasm_val_vec_t* results);
-```
+The engine itself is Rust (`crates/xrpl-wasm-vm`, over wasmi), reached through a cxx
+bridge.
 
-### 5. Implement Wrapper in detail/HostFuncWrapper.cpp
+## What is in this directory
 
-Implement the C-style wrapper that bridges WASM to C++:
+- **`WasmVM.h`** — the entry points xrpld calls: `runEscrowWasm` (execute a contract,
+  returning a result and its gas cost, or a `WasmTER`) and `preflightEscrowWasm` (screen a
+  module with no host and no execution). Both own their TER maps.
+- **`HostFunc.h`** — the `HostFunctions` interface: one virtual per host function, each
+  defaulting to `Unimplemented`, returning `std::expected<T, HostFunctionError>`.
+- **`HostFuncImpl.h`** — `WasmHostFunctionsImpl`, the implementation over an
+  `ApplyContext&`. Bodies are split across `HostFuncImpl*.cpp` by category.
+- **`HostContext.h`** — the bridge's C++ half: an ABI-shaped, `noexcept` view of
+  `HostFunctions` that the engine calls back into. Nothing may unwind into Rust, so every
+  method routes through `guarded()`.
+- **`WasmCommon.h`** — the shared vocabulary: `HostFunctionError` (the codes a contract
+  sees), `Bytes`, `FieldLocator`, `WasmTER`, `adjustWasmEndianess`, which is where the
+  boundary's byte order is decided, and `guarded()`, the one catch every crossing of the
+  bridge's C++ half goes through.
 
-```cpp
-wasm_trap_t*
-myNewFunction_wrap(void* env, wasm_val_vec_t const* params, wasm_val_vec_t* results)
-{
-    // Extract parameters from params
-    // Call hfs->myNewFunction(...)
-    // Set results and return
-}
-```
+## Host functions
 
-### 6. Register in WasmVM.cpp
+Grouped by what they reach: ledger information; transaction and ledger-object field access;
+keylet construction; cryptography; float arithmetic; NFT queries; tracing.
 
-Add the function registration in `setCommonHostFunctions()` or
-`createWasmImport()`:
+The wire names and per-call gas costs are declared in `crates/xrpl-host-functions` —
+one `host_functions!` block that generates the ABI trait and the spec table. That
+declaration is the single source of truth; `HostFunc.h` is the C++ side of it.
 
-```cpp
-WASM_IMPORT_FUNC2(i, myNewFunction, "my_new_function", hfs, 100);
-//                                   ^^ WASM name       ^^ gas cost
-```
+## Entry point
 
-> [!IMPORTANT]
-> New host functions MUST be amendment-gated in `WasmVM.cpp`.
-> Wrap the registration in an amendment check to ensure the function is only
-> available after the corresponding amendment is enabled on the network.
+A module must export `escrow_finish` (`escrowFunctionName`) taking no parameters and
+returning `int32_t`: positive means the conditions are met, zero or negative rejects the
+finish. Everything the contract needs it asks for through a host call.
diff --git a/include/xrpl/tx/wasm/WasmCommon.h b/include/xrpl/tx/wasm/WasmCommon.h
index f73ca7c2d26..fa651bef105 100644
--- a/include/xrpl/tx/wasm/WasmCommon.h
+++ b/include/xrpl/tx/wasm/WasmCommon.h
@@ -1,16 +1,18 @@
 #pragma once
 
+#include <xrpl/basics/Log.h>
 #include <xrpl/basics/base_uint.h>
 #include <xrpl/basics/contract.h>
+#include <xrpl/beast/utility/Journal.h>
 #include <xrpl/protocol/TER.h>
 
 #include <bit>
 #include <cstddef>
 #include <cstdint>
-#include <functional>
+#include <exception>
 #include <optional>
+#include <source_location>
 #include <stdexcept>
-#include <string_view>
 #include <type_traits>
 #include <utility>
 #include <vector>
@@ -21,30 +23,6 @@ using Bytes = std::vector<std::uint8_t>;
 using Hash = xrpl::uint256;
 using FloatPair = std::pair<int64_t, int32_t>;
 
-// Error signals that cross the wasm boundary as trap messages (the C API has no
-// trap code). WasmiEngine::call maps them to TER: hfErrInternal -> tecINTERNAL,
-// hfErrOutOfGas / wasmi's OutOfFuel -> tecOUT_OF_GAS, anything else ->
-// tecFAILED_PROCESSING.
-//
-// Matched as substrings, not by equality: the C API returns the Rust Debug form
-// of the error, e.g. `Error { kind: Message("HfInternal") }` or
-// `Error { kind: TrapCode(OutOfFuel) }`.
-std::string_view inline constexpr hfErrInternal = "HfInternal";
-std::string_view inline constexpr hfErrOutOfGas = "HfOutOfGas";
-std::string_view inline constexpr wasmiTrapOutOfFuel = "OutOfFuel";
-
-// Guest ABI, mirrored in the wasm stdlib: append only, never renumber. Starts at
-// 1 so a zeroed data_type is rejected rather than treated as Int64.
-enum class TraceDataType : std::int32_t {
-    Int64 = 1,
-    Uint64,
-    Xfloat,
-    Account,
-    Amount,
-    AsHex,   // raw bytes, hex-encoded by the host before printing
-    AsText,  // bytes printed verbatim as text
-};
-
 enum class HostFunctionError : int32_t {
     Unimplemented = -1,
     FieldNotFound = -2,
@@ -68,19 +46,6 @@ enum class HostFunctionError : int32_t {
     FloatComputationError = -20,
 };
 
-enum class WasmTypes { WtI32, WtI64 };
-
-struct Wmem
-{
-    std::uint8_t* p = nullptr;
-    std::size_t s = 0;
-
-    Wmem() = default;
-    Wmem(void* ptr, std::size_t size) : p(reinterpret_cast<std::uint8_t*>(ptr)), s(size)
-    {
-    }
-};
-
 template <typename T>
 struct WasmResult
 {
@@ -148,71 +113,6 @@ class FieldLocator
     }
 };
 
-class WasmRuntimeWrapper
-{
-public:
-    virtual ~WasmRuntimeWrapper() = default;
-
-    virtual Wmem
-    getMem() = 0;
-
-    virtual std::int64_t
-    getGas() = 0;
-
-    virtual std::int64_t
-    setGas(std::int64_t gas) = 0;
-
-    virtual std::int64_t
-    getTransferLimit() = 0;
-
-    virtual std::int64_t
-    setTransferLimit(std::int64_t transferLimit) = 0;
-};
-using RTOptRef = std::optional<std::reference_wrapper<WasmRuntimeWrapper>>;
-
-struct WasmParam
-{
-    // We are not supporting float/double
-
-    WasmTypes type = WasmTypes::WtI32;
-    union
-    {
-        std::int32_t i32;
-        std::int64_t i64 = 0;
-    } of;
-};
-
-template <class... Types>
-inline void
-wasmParamsHlp(std::vector<WasmParam>& v, std::int32_t p, Types&&... args)
-{
-    v.push_back({.type = WasmTypes::WtI32, .of = {.i32 = p}});
-    wasmParamsHlp(v, std::forward<Types>(args)...);
-}
-
-template <class... Types>
-inline void
-wasmParamsHlp(std::vector<WasmParam>& v, std::int64_t p, Types&&... args)
-{
-    v.push_back({.type = WasmTypes::WtI64, .of = {.i64 = p}});
-    wasmParamsHlp(v, std::forward<Types>(args)...);
-}
-
-inline void
-wasmParamsHlp(std::vector<WasmParam>& v)
-{
-}
-
-template <class... Types>
-inline std::vector<WasmParam>
-wasmParams(Types&&... args)
-{
-    std::vector<WasmParam> v;
-    v.reserve(sizeof...(args));
-    wasmParamsHlp(v, std::forward<Types>(args)...);
-    return v;
-}
-
 template <typename T, size_t Size = sizeof(T)>
 constexpr T
 adjustWasmEndianessHlp(T x)
@@ -250,4 +150,28 @@ hfErrorToInt(HostFunctionError e)
     return static_cast<int32_t>(e);
 }
 
+template <class Body>
+std::invoke_result_t<Body>
+guarded(
+    beast::Journal journal,
+    std::invoke_result_t<Body> onThrow,
+    Body&& body,
+    std::source_location const location = std::source_location::current()) noexcept
+{
+    try
+    {
+        return body();
+    }
+    catch (std::exception const& e)
+    {
+        JLOG(journal.error()) << "wasm: " << location.function_name() << " threw: " << e.what();
+    }
+    catch (...)
+    {
+        JLOG(journal.error()) << "wasm: " << location.function_name() << " threw";
+    }
+
+    return onThrow;
+}
+
 }  // namespace xrpl
diff --git a/include/xrpl/tx/wasm/WasmImportsHelper.h b/include/xrpl/tx/wasm/WasmImportsHelper.h
deleted file mode 100644
index 0c31e969c15..00000000000
--- a/include/xrpl/tx/wasm/WasmImportsHelper.h
+++ /dev/null
@@ -1,126 +0,0 @@
-#pragma once
-
-#include <xrpl/tx/wasm/HostFunc.h>
-#include <xrpl/tx/wasm/WasmCommon.h>
-
-#include <boost/function_types/function_arity.hpp>
-#include <boost/function_types/parameter_types.hpp>
-#include <boost/function_types/result_type.hpp>
-#include <boost/mpl/vector.hpp>
-
-#include <wasm.h>
-
-#include <cstdint>
-#include <optional>
-#include <string_view>
-#include <unordered_map>
-#include <utility>
-#include <vector>
-
-namespace bft = boost::function_types;
-
-namespace xrpl {
-
-using wasmSecondaryCbFuncType =
-    wasm_trap_t*(HostFunctions&, wasm_val_vec_t const*, wasm_val_vec_t*);
-
-struct WasmImportFunc
-{
-    std::string_view name;
-    std::optional<WasmTypes> result;
-    std::vector<WasmTypes> params;
-
-    wasmSecondaryCbFuncType* wrap = nullptr;
-    uint32_t gas = 0;
-};
-
-using WasmUserData = std::pair<HFRef, WasmImportFunc>;
-// string - import function name
-using ImportVec = std::unordered_map<std::string_view, WasmUserData>;
-
-template <int N, int C, typename Mpl>
-void
-WasmImpArgs(WasmImportFunc& e)
-{
-    if constexpr (N < C)
-    {
-        using at = boost::mpl::at_c<Mpl, N>::type;
-        if constexpr (std::is_pointer_v<at> || std::is_same_v<at, std::int32_t>)
-        {
-            e.params.push_back(WasmTypes::WtI32);
-        }
-        else if constexpr (std::is_same_v<at, std::int64_t>)
-        {
-            e.params.push_back(WasmTypes::WtI64);
-        }
-        else
-        {
-            static_assert(std::is_pointer_v<at>, "Unsupported argument type");
-        }
-
-        return WasmImpArgs<N + 1, C, Mpl>(e);
-    }
-}
-
-template <typename>
-inline constexpr bool wasmDependentFalse = false;
-
-template <typename Rt>
-void
-WasmImpRet(WasmImportFunc& e)
-{
-    if constexpr (std::is_pointer_v<Rt> || std::is_same_v<Rt, std::int32_t>)
-    {
-        e.result = WasmTypes::WtI32;
-    }
-    else if constexpr (std::is_same_v<Rt, std::int64_t>)
-    {
-        e.result = WasmTypes::WtI64;
-    }
-    else if constexpr (std::is_void_v<Rt>)
-    {
-        e.result.reset();
-    }
-    else
-    {
-        static_assert(wasmDependentFalse<Rt>, "Unsupported return type");
-    }
-}
-
-template <typename F>
-void
-WasmImpFuncHelper(WasmImportFunc& e)
-{
-    using rt = bft::result_type<F>::type;
-    using pt = bft::parameter_types<F>::type;
-    // typename boost::mpl::at_c<mpl, N>::type
-
-    WasmImpRet<rt>(e);
-    WasmImpArgs<0, bft::function_arity<F>::value, pt>(e);
-    // WasmImpWrap(e, std::forward<F>(f));
-}
-
-// imp_name - string literal, must have static lifetime
-template <typename F>
-void
-WasmImpFunc(
-    ImportVec& v,
-    std::string_view impName,
-    wasmSecondaryCbFuncType* fWrap,
-    HostFunctions& hf,
-    uint32_t gas = 0)
-{
-    WasmImportFunc e;
-    e.name = impName;
-    e.wrap = fWrap;
-    e.gas = gas;
-    WasmImpFuncHelper<F>(e);
-    v.emplace(impName, std::make_pair(HFRef(hf), std::move(e)));
-}
-
-#define WASM_IMPORT_FUNC(v, f, ...) WasmImpFunc<f##_proto>(v, #f, &f##_wrap, ##__VA_ARGS__)
-
-// n - string literal name, must have static lifetime
-#define WASM_IMPORT_FUNC2(v, f, n, ...) WasmImpFunc<f##_proto>(v, n, &f##_wrap, ##__VA_ARGS__)
-
-}  // namespace xrpl
diff --git a/include/xrpl/tx/wasm/WasmVM.h b/include/xrpl/tx/wasm/WasmVM.h
index e20488de00d..99161b93afe 100644
--- a/include/xrpl/tx/wasm/WasmVM.h
+++ b/include/xrpl/tx/wasm/WasmVM.h
@@ -4,94 +4,47 @@
 #include <xrpl/protocol/TER.h>
 #include <xrpl/tx/wasm/HostFunc.h>
 #include <xrpl/tx/wasm/WasmCommon.h>
-#include <xrpl/tx/wasm/WasmImportsHelper.h>
 
 #include <cstdint>
 #include <expected>
-#include <memory>
-#include <string>
 #include <string_view>
-#include <vector>
 
 namespace xrpl {
 
-std::string_view inline constexpr wEnv = "env";
-std::string_view inline constexpr wHostLib = "host_lib";
-std::string_view inline constexpr wMem = "memory";
-std::string_view inline constexpr wStore = "store";
-std::string_view inline constexpr wLoad = "load";
-std::string_view inline constexpr wSize = "size";
-std::string_view inline constexpr wAlloc = "allocate";
-std::string_view inline constexpr wDealloc = "deallocate";
-std::string_view inline constexpr wProcExit = "proc_exit";
-
+// The export a programmable escrow's contract is run through.
 std::string_view inline constexpr escrowFunctionName = "escrow_finish";
 
-uint32_t inline constexpr maxPages = 128;  // 8MB = 64KB*128
-
-class WasmiEngine;
-
-class WasmEngine
-{
-    std::unique_ptr<WasmiEngine> const impl_;
-
-    WasmEngine();
-
-public:
-    WasmEngine(WasmEngine const&) = delete;
-    WasmEngine(WasmEngine&&) = delete;
-    WasmEngine&
-    operator=(WasmEngine const&) = delete;
-    WasmEngine&
-    operator=(WasmEngine&&) = delete;
-
-    static WasmEngine&
-    instance();
-
-    std::expected<WasmResult<int32_t>, WasmTER>
-    run(Bytes const& wasmCode,
-        HostFunctions& hfs,
-        int64_t gasLimit,
-        std::string_view funcName = {},
-        std::vector<WasmParam> const& params = {},
-        ImportVec const& imports = {},
-        beast::Journal j = beast::Journal{beast::Journal::getNullSink()});
-
-    NotTEC
-    check(
-        Bytes const& wasmCode,
-        HostFunctions& hfs,
-        std::string_view funcName,
-        std::vector<WasmParam> const& params = {},
-        ImportVec const& imports = {},
-        beast::Journal j = beast::Journal{beast::Journal::getNullSink()});
-
-    // Host functions helper functionality
-    void*
-    newTrap(std::string const& txt = std::string());
-
-    [[nodiscard]] beast::Journal
-    getJournal() const;
-};
-
-////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
-
-ImportVec
-createWasmImport(HostFunctions& hfs);
-
+// Run `wasmCode`'s `funcName` export with `gasLimit` gas, servicing its host calls
+// through `hfs`.
+//
+// On success the result is what the contract returned - positive means the escrow may
+// finish - together with the gas it consumed. On failure it is the TER to apply and,
+// when the number means anything, the gas to write to transaction metadata: a contract
+// that traps or exhausts its budget is charged for what it burned, while a `tecINTERNAL`
+// reports no cost because the fault is the node's rather than the transaction's.
 std::expected<EscrowResult, WasmTER>
 runEscrowWasm(
     Bytes const& wasmCode,
     HostFunctions& hfs,
-    int64_t gasLimit,
-    std::string_view funcName = escrowFunctionName,
-    std::vector<WasmParam> const& params = {});
-
+    std::int64_t gasLimit,
+    std::string_view funcName = escrowFunctionName) noexcept;
+
+// Screen `wasmCode`: whether `runEscrowWasm` would refuse it before the contract's
+// first instruction. Compiles the module and reads its imports and exports; runs
+// nothing.
+//
+// Takes no `HostFunctions`, because the verdict comes from the compiled module alone.
+// That is what makes this callable from a transactor's `preflight`, which has no view
+// to build a host over.
+//
+// `temBAD_WASM` for every fault in the module - the transaction carries something this
+// engine cannot run, so it is refused before it can reach the ledger.
+// `telFAILED_PROCESSING` if the engine itself failed: nothing was learned about the
+// module, and a defect here is not evidence that the transaction is malformed.
 NotTEC
 preflightEscrowWasm(
     Bytes const& wasmCode,
-    HostFunctions& hfs,
-    std::string_view funcName = escrowFunctionName,
-    std::vector<WasmParam> const& params = {});
+    beast::Journal j,
+    std::string_view funcName = escrowFunctionName) noexcept;
 
 }  // namespace xrpl
diff --git a/include/xrpl/tx/wasm/WasmiVM.h b/include/xrpl/tx/wasm/WasmiVM.h
deleted file mode 100644
index 5a72cd35f67..00000000000
--- a/include/xrpl/tx/wasm/WasmiVM.h
+++ /dev/null
@@ -1,462 +0,0 @@
-#pragma once
-
-#include <xrpl/basics/contract.h>
-#include <xrpl/beast/utility/Journal.h>
-#include <xrpl/protocol/Protocol.h>
-#include <xrpl/protocol/TER.h>
-#include <xrpl/tx/wasm/HostFunc.h>
-#include <xrpl/tx/wasm/WasmCommon.h>
-#include <xrpl/tx/wasm/WasmImportsHelper.h>
-#include <xrpl/tx/wasm/WasmVM.h>
-
-#include <wasm.h>
-
-#include <cstddef>
-#include <cstdint>
-#include <expected>
-#include <memory>
-#include <mutex>
-#include <optional>
-#include <stdexcept>
-#include <string>
-#include <string_view>
-#include <type_traits>
-#include <utility>
-#include <vector>
-
-namespace xrpl {
-
-template <class T, void (*Create)(T*, size_t), void (*Destroy)(T*)>
-class WasmVec
-{
-    using TD = std::remove_pointer_t<decltype(T::data)>;
-    T vec_;
-
-public:
-    WasmVec(size_t s = 0) : vec_ WASM_EMPTY_VEC
-    {
-        if (s > 0)
-            Create(&vec_, s);  // zeroes memory
-    }
-
-    ~WasmVec()
-    {
-        clear();
-    }
-
-    WasmVec(WasmVec const&) = delete;
-    WasmVec&
-    operator=(WasmVec const&) = delete;
-
-    WasmVec(WasmVec&& other) noexcept : vec_ WASM_EMPTY_VEC
-    {
-        *this = std::move(other);
-    }
-
-    WasmVec&
-    operator=(WasmVec&& other) noexcept
-    {
-        if (this != &other)
-        {
-            clear();
-            vec_ = other.vec_;
-            other.vec_ = WASM_EMPTY_VEC;
-        }
-        return *this;
-    }
-
-    void
-    clear()
-    {
-        Destroy(&vec_);  // call destructor for every elements too
-        vec_ = WASM_EMPTY_VEC;
-    }
-
-    T
-    release()
-    {
-        T result = vec_;
-        vec_ = WASM_EMPTY_VEC;
-        return result;
-    }
-
-    T*
-    get()
-    {
-        return &vec_;
-    }
-
-    [[nodiscard]] T const*
-    get() const
-    {
-        return &vec_;
-    }
-
-    TD&
-    operator[](size_t i)
-    {
-        if (i >= vec_.size)
-            Throw<std::runtime_error>("Out of bound");
-        return vec_.data[i];
-    }
-
-    TD const&
-    operator[](size_t i) const
-    {
-        if (i >= vec_.size)
-            Throw<std::runtime_error>("Out of bound");
-        return vec_.data[i];
-    }
-
-    [[nodiscard]] size_t
-    size() const
-    {
-        return vec_.size;
-    }
-
-    [[nodiscard]] bool
-    empty() const
-    {
-        return vec_.size == 0u;
-    }
-};
-
-using WasmValtypeVec =
-    WasmVec<wasm_valtype_vec_t, &wasm_valtype_vec_new_uninitialized, &wasm_valtype_vec_delete>;
-using WasmValVec = WasmVec<wasm_val_vec_t, &wasm_val_vec_new_uninitialized, &wasm_val_vec_delete>;
-using WasmExternVec =
-    WasmVec<wasm_extern_vec_t, &wasm_extern_vec_new_uninitialized, &wasm_extern_vec_delete>;
-using WasmExporttypeVec = WasmVec<
-    wasm_exporttype_vec_t,
-    &wasm_exporttype_vec_new_uninitialized,
-    &wasm_exporttype_vec_delete>;
-using WasmImporttypeVec = WasmVec<
-    wasm_importtype_vec_t,
-    &wasm_importtype_vec_new_uninitialized,
-    &wasm_importtype_vec_delete>;
-
-struct WasmiResult
-{
-    WasmValVec r;
-    // Set iff the call trapped. Holds the TER the trap was classified into
-    // (tecINTERNAL / tecOUT_OF_GAS / tecFAILED_PROCESSING); see
-    // WasmiEngine::call. std::nullopt means the call returned normally.
-    std::optional<TER> ter;
-
-    WasmiResult(unsigned n = 0) : r(n)
-    {
-    }
-
-    WasmiResult() = delete;
-    ~WasmiResult() = default;
-    WasmiResult(WasmiResult&& o) = default;
-    WasmiResult&
-    operator=(WasmiResult&& o) = default;
-};
-
-using ModulePtr = std::unique_ptr<wasm_module_t, decltype(&wasm_module_delete)>;
-using InstancePtr = std::unique_ptr<wasm_instance_t, decltype(&wasm_instance_delete)>;
-using EnginePtr = std::unique_ptr<wasm_engine_t, decltype(&wasm_engine_delete)>;
-using StorePtr = std::unique_ptr<wasm_store_t, decltype(&wasm_store_delete)>;
-
-using FuncInfo = std::pair<wasm_func_t const*, wasm_functype_t const*>;
-
-class InstanceWrapper
-{
-    wasm_store_t* store_ = nullptr;
-    WasmExternVec exports_;
-    mutable int memIdx_ = -1;
-    InstancePtr instance_;
-    beast::Journal j_ = beast::Journal(beast::Journal::getNullSink());
-    std::int64_t transferLimit_ = kWasmTransferLimit;
-
-private:
-    static InstancePtr
-    init(
-        StorePtr& s,
-        ModulePtr& m,
-        WasmExternVec& expt,
-        WasmExternVec const& imports,
-        beast::Journal j);
-
-public:
-    InstanceWrapper() : instance_(nullptr, &wasm_instance_delete) {};
-
-    InstanceWrapper(InstanceWrapper const&) = delete;
-
-    InstanceWrapper(InstanceWrapper&& o) : instance_(nullptr, &wasm_instance_delete)
-    {
-        *this = std::move(o);  // LCOV_EXCL_LINE
-    }
-
-    InstanceWrapper(StorePtr& s, ModulePtr& m, WasmExternVec const& imports, beast::Journal j)
-        : store_(s.get()), instance_(init(s, m, exports_, imports, j)), j_(j)
-    {
-    }
-
-    InstanceWrapper&
-    operator=(InstanceWrapper&& o);
-
-    InstanceWrapper&
-    operator=(InstanceWrapper const&) = delete;
-
-    operator bool() const
-    {
-        return static_cast<bool>(instance_);
-    }
-
-    FuncInfo
-    getFunc(std::string_view funcName, WasmExporttypeVec const& exportTypes) const;
-
-    Wmem
-    getMem() const;
-
-    std::int64_t
-    getGas() const;
-
-    std::int64_t
-    setGas(std::int64_t) const;
-
-    std::int64_t
-    getTransferLimit() const;
-
-    std::int64_t
-    setTransferLimit(std::int64_t);
-};
-
-class ModuleWrapper
-{
-    ModulePtr module_;
-    InstanceWrapper instanceWrap_;
-    WasmExporttypeVec exportTypes_;
-    beast::Journal j_ = beast::Journal(beast::Journal::getNullSink());
-
-public:
-    // LCOV_EXCL_START
-    ModuleWrapper() : module_(nullptr, &wasm_module_delete)
-    {
-    }
-
-    ModuleWrapper(ModuleWrapper&& o) : module_(nullptr, &wasm_module_delete)
-    {
-        *this = std::move(o);
-    }
-    // LCOV_EXCL_STOP
-
-    ModuleWrapper&
-    operator=(ModuleWrapper&& o);
-    ModuleWrapper(
-        StorePtr& s,
-        Bytes const& wasmBin,
-        bool instantiate,
-        ImportVec const& imports,
-        beast::Journal j);
-    ~ModuleWrapper() = default;
-
-    operator bool() const
-    {
-        return instanceWrap_;
-    }
-
-    FuncInfo
-    getFunc(std::string_view funcName) const
-    {
-        return instanceWrap_.getFunc(funcName, exportTypes_);
-    }
-
-    wasm_functype_t const*
-    getFuncType(std::string_view funcName) const;
-
-    Wmem
-    getMem() const
-    {
-        return instanceWrap_.getMem();
-    }
-
-    InstanceWrapper&
-    getInstance(int i = 0)
-    {
-        return instanceWrap_;
-    }
-
-    InstanceWrapper const&
-    getInstance(int i = 0) const
-    {
-        return instanceWrap_;
-    }
-
-    int
-    addInstance(StorePtr& s, WasmExternVec const& imports)
-    {
-        instanceWrap_ = {s, module_, imports, j_};
-        return 0;
-    }
-
-    std::int64_t
-    getGas() const
-    {
-        return instanceWrap_ ? instanceWrap_.getGas() : -1;
-    }
-
-private:
-    static ModulePtr
-    init(StorePtr& s, Bytes const& wasmBin, beast::Journal j);
-
-    WasmExternVec
-    buildImports(StorePtr& s, ImportVec const& imports) const;
-};
-
-class WasmiEngine
-{
-    EnginePtr engine_;
-    StorePtr store_;
-    std::unique_ptr<ModuleWrapper> moduleWrap_;
-    beast::Journal j_ = beast::Journal(beast::Journal::getNullSink());
-
-    std::mutex m_;  // 1 instance mutex
-
-public:
-    WasmiEngine() : engine_(init()), store_(nullptr, &wasm_store_delete)
-    {
-    }
-
-    ~WasmiEngine() = default;
-
-    static EnginePtr
-    init();
-
-    std::expected<WasmResult<int32_t>, WasmTER>
-    run(Bytes const& wasmCode,
-        HostFunctions& hfs,
-        int64_t gas,
-        std::string_view funcName,
-        std::vector<WasmParam> const& params,
-        ImportVec const& imports,
-        beast::Journal j);
-
-    NotTEC
-    check(
-        Bytes const& wasmCode,
-        HostFunctions& hfs,
-        std::string_view funcName,
-        std::vector<WasmParam> const& params,
-        ImportVec const& imports,
-        beast::Journal j);
-
-    [[nodiscard]] std::int64_t
-    getGas() const
-    {
-        return moduleWrap_ ? moduleWrap_->getGas() : -1;  // LCOV_EXCL_LINE
-    }
-
-    // Host functions helper functionality
-    wasm_trap_t*
-    newTrap(std::string const& msg);
-
-    // LCOV_EXCL_START
-    [[nodiscard]] beast::Journal
-    getJournal() const
-    {
-        return j_;
-    }
-    // LCOV_EXCL_STOP
-
-private:
-    [[nodiscard]] InstanceWrapper&
-    getRT(int m = 0, int i = 0) const
-    {
-        if (!moduleWrap_)
-            Throw<std::runtime_error>("no module");
-        return moduleWrap_->getInstance(i);
-    }
-
-    [[nodiscard]] Wmem
-    getMem() const
-    {
-        return moduleWrap_ ? moduleWrap_->getMem() : Wmem();
-    }
-
-    std::expected<WasmResult<int32_t>, WasmTER>
-    runHlp(
-        Bytes const& wasmCode,
-        HostFunctions& hfs,
-        int64_t gas,
-        std::string_view funcName,
-        std::vector<WasmParam> const& params,
-        ImportVec const& imports,
-        beast::Journal j);
-
-    NotTEC
-    checkHlp(
-        Bytes const& wasmCode,
-        HostFunctions& hfs,
-        std::string_view funcName,
-        std::vector<WasmParam> const& params,
-        ImportVec const& imports,
-        beast::Journal j);
-
-    int
-    addModule(Bytes const& wasmCode, bool instantiate, ImportVec const& imports, int64_t gas);
-    void
-    clearModules();
-
-    // int  addInstance();
-
-    int32_t
-    runFunc(std::string_view const funcName, int32_t p);
-
-    int32_t
-    makeModule(Bytes const& wasmCode, WasmExternVec const& imports = {});
-
-    [[nodiscard]] FuncInfo
-    getFunc(std::string_view funcName) const
-    {
-        return moduleWrap_->getFunc(funcName);
-    }
-
-    static std::vector<wasm_val_t>
-    convertParams(std::vector<WasmParam> const& params);
-
-    static int
-    compareParamTypes(wasm_valtype_vec_t const* ftp, std::vector<wasm_val_t> const& p);
-
-    static void
-    addParam(std::vector<wasm_val_t>& in, int32_t p);
-    static void
-    addParam(std::vector<wasm_val_t>& in, int64_t p);
-
-    template <int NR, class... Types>
-    inline WasmiResult
-    call(std::string_view func, Types&&... args);
-
-    template <int NR, class... Types>
-    inline WasmiResult
-    call(FuncInfo const& f, Types&&... args);
-
-    template <int NR, class... Types>
-    inline WasmiResult
-    call(FuncInfo const& f, std::vector<wasm_val_t>& in);
-
-    template <int NR, class... Types>
-    inline WasmiResult
-    call(FuncInfo const& f, std::vector<wasm_val_t>& in, std::int32_t p, Types&&... args);
-
-    template <int NR, class... Types>
-    inline WasmiResult
-    call(FuncInfo const& f, std::vector<wasm_val_t>& in, std::int64_t p, Types&&... args);
-
-    template <int NR, class... Types>
-    inline WasmiResult
-    call(
-        FuncInfo const& f,
-        std::vector<wasm_val_t>& in,
-        uint8_t const* d,
-        int32_t sz,
-        Types&&... args);
-
-    template <int NR, class... Types>
-    inline WasmiResult
-    call(FuncInfo const& f, std::vector<wasm_val_t>& in, Bytes const& p, Types&&... args);
-};
-
-}  // namespace xrpl
diff --git a/src/libxrpl/tx/wasm/HostContext.cpp b/src/libxrpl/tx/wasm/HostContext.cpp
new file mode 100644
index 00000000000..1c35789bdfc
--- /dev/null
+++ b/src/libxrpl/tx/wasm/HostContext.cpp
@@ -0,0 +1,223 @@
+#include <xrpl/tx/wasm/HostContext.h>
+
+#include <xrpl/basics/Slice.h>
+#include <xrpl/basics/base_uint.h>
+#include <xrpl/basics/strHex.h>
+#include <xrpl/protocol/AccountID.h>
+#include <xrpl/protocol/Protocol.h>
+#include <xrpl/protocol/SField.h>
+#include <xrpl/protocol/STAmount.h>
+#include <xrpl/protocol/Serializer.h>
+#include <xrpl/tx/wasm/HostFunc.h>
+#include <xrpl/tx/wasm/WasmCommon.h>
+
+#include <rust/cxx.h>
+// For `TraceDataType`, which the bridge declares and this header defines.
+#include <xrpl_wasm_vm_ffi_cxxbridge/lib.h>
+
+#include <cstddef>
+#include <cstdint>
+#include <cstring>
+#include <exception>
+#include <optional>
+#include <string>
+#include <string_view>
+#include <type_traits>
+
+namespace xrpl {
+
+namespace {
+
+// What a host call answers when it could not be served at all: every method below hands it
+// to `guarded` as the answer for a body that throws. The engine reads -1 as its fatal
+// `Internal`, stops the run and reports `tecINTERNAL`.
+//
+// `HostFunctionError` spells -1 `Unimplemented`, so the two share a code. They also share
+// a meaning worth keeping together - "the host could not serve this call, and the contract
+// has no business interpreting why" - and they must share a fate. Named here so a call
+// site reads as what it is rather than as "unimplemented".
+constexpr std::int32_t kHostInternal = hfErrorToInt(HostFunctionError::Unimplemented);
+
+// Copy `value` into `out` only if the whole of it fits, and answer its true length either
+// way. A value too large for the guest's buffer must reach it in no part: a prefix would
+// be a wrong answer where a length is a usable one.
+std::int32_t
+answer(rust::Slice<std::uint8_t> out, std::uint8_t const* value, std::size_t size)
+{
+    if (size <= out.size())
+        std::memcpy(out.data(), value, size);
+    return static_cast<std::int32_t>(size);
+}
+
+// A scalar the ABI carries as bytes, in the wire's byte order.
+//
+// `adjustWasmEndianess` is the one place that order is decided for the whole wasm boundary,
+// and it is `constexpr` with the swap under `if constexpr (std::endian::native ==
+// std::endian::big)` - so this costs nothing on a little-endian host and is correct on a
+// big-endian one, which a hand-written shift sequence per call site would have to get right
+// each time.
+template <class T>
+std::int32_t
+answerScalar(rust::Slice<std::uint8_t> out, T value)
+{
+    auto const wire = adjustWasmEndianess(value);
+    return answer(out, reinterpret_cast<std::uint8_t const*>(&wire), sizeof(wire));
+}
+
+// A traced integer, which the guest sends as bytes rather than as a wasm scalar so that one
+// import serves every type. `std::nullopt` if the buffer is not the width the type needs.
+//
+// `memcpy` regardless of alignment, and no `reinterpret_cast` fast path: a trace must cost
+// the same whatever address the guest chose for its buffer.
+template <class T>
+std::optional<T>
+traceInt(Slice const& data)
+{
+    static_assert(std::is_integral_v<T>);
+    if (data.size() != sizeof(T))
+        return std::nullopt;
+
+    T x;
+    std::memcpy(&x, data.data(), sizeof(T));
+    return adjustWasmEndianess(x);
+}
+
+// The guest's bytes as the text a log line carries, or `std::nullopt` when they do not hold
+// the type they claim.
+//
+// The engine refuses a code that names no type before it crosses, so `type` is always one of
+// the variants; the trailing `return` is what the `switch` owes a scoped enum, not a case
+// this can meet.
+//
+// May throw: `STAmount`'s deserializer rejects malformed input that way.
+std::optional<std::string>
+traceFormat(TraceDataType type, Slice const& data)
+{
+    switch (type)
+    {
+        case TraceDataType::Int64:
+            if (auto const x = traceInt<std::int64_t>(data))
+                return std::to_string(*x);
+            return std::nullopt;
+
+        case TraceDataType::Uint64:
+            if (auto const x = traceInt<std::uint64_t>(data))
+                return std::to_string(*x);
+            return std::nullopt;
+
+        case TraceDataType::Xfloat:
+            return wasm_float::floatToString(data);
+
+        case TraceDataType::Account:
+            if (data.size() != AccountID::size())
+                return std::nullopt;
+            return toBase58(AccountID::fromVoid(data.data()));
+
+        case TraceDataType::Amount: {
+            SerialIter iter(data);
+            STAmount const amount(iter, sfGeneric);
+            return amount.getFullText();
+        }
+
+        case TraceDataType::AsHex:
+            return strHex(data);
+
+        case TraceDataType::AsText:
+            // An empty Slice has a null data(), which std::string may not be handed.
+            if (data.empty())
+                return std::string();
+            return std::string(reinterpret_cast<char const*>(data.data()), data.size());
+    }
+
+    return std::nullopt;
+}
+
+}  // namespace
+
+HostContext::HostContext(HostFunctions& hostFunctions) : hostFunctions_(hostFunctions)
+{
+}
+
+std::int32_t
+HostContext::getLedgerSqn(rust::Slice<std::uint8_t> out) const noexcept
+{
+    return guarded(hostFunctions_.getJournal(), kHostInternal, [&] {
+        auto const sqn = hostFunctions_.getLedgerSqn();
+        if (!sqn)
+            return hfErrorToInt(sqn.error());
+
+        return answerScalar(out, *sqn);
+    });
+}
+
+std::int32_t
+HostContext::getCurrentLedgerObjField(std::int32_t field, rust::Slice<std::uint8_t> out)
+    const noexcept
+{
+    return guarded(hostFunctions_.getJournal(), kHostInternal, [&] {
+        auto const& knownSFields = SField::getKnownCodeToField();
+        auto const it = knownSFields.find(field);
+        if (it == knownSFields.end())
+            return hfErrorToInt(HostFunctionError::InvalidField);
+
+        auto const value = hostFunctions_.getCurrentLedgerObjField(*it->second);
+        if (!value)
+            return hfErrorToInt(value.error());
+
+        return answer(out, value->data(), value->size());
+    });
+}
+
+std::int32_t
+HostContext::sha512Half(rust::Slice<std::uint8_t const> data, rust::Slice<std::uint8_t> out)
+    const noexcept
+{
+    return guarded(hostFunctions_.getJournal(), kHostInternal, [&] {
+        auto const digest = hostFunctions_.computeSha512HalfHash(Slice{data.data(), data.size()});
+        if (!digest)
+            return hfErrorToInt(digest.error());
+
+        return answer(out, digest->data(), digest->size());
+    });
+}
+
+void
+HostContext::trace(rust::Str msg, rust::Slice<std::uint8_t const> data, TraceDataType dataType)
+    const noexcept
+{
+    auto const journal = hostFunctions_.getJournal();
+
+    // Not `guarded`: a buffer that does not hold what it claims is an ordinary contract
+    // mistake, so it belongs in the log the contract is writing to rather than in the error
+    // log as an internal failure - and it must not become one, since there is nothing to
+    // report it to.
+    try
+    {
+        if (msg.size() + data.size() > kMaxWasmDataLength)
+        {
+            JLOG(journal.trace()) << "WasmTrace: message and data too long";
+            return;
+        }
+
+        // Rendered whatever the log level: the level decides what is written, never whether
+        // the host is called, so a run costs the same on every node.
+        auto const text = traceFormat(dataType, Slice{data.data(), data.size()});
+        if (!text)
+        {
+            JLOG(journal.trace()) << "WasmTrace: data does not hold the type it names";
+            return;
+        }
+
+        hostFunctions_.trace(std::string_view{msg.data(), msg.size()}, *text);
+    }
+    catch (std::exception const& e)
+    {
+        JLOG(journal.trace()) << "WasmTrace: threw: " << e.what();
+    }
+    catch (...)
+    {
+        JLOG(journal.trace()) << "WasmTrace: threw";
+    }
+}
+
+}  // namespace xrpl
diff --git a/src/libxrpl/tx/wasm/HostFuncImplGetter.cpp b/src/libxrpl/tx/wasm/HostFuncImplGetter.cpp
index 4ae0c724268..e622e62b0b8 100644
--- a/src/libxrpl/tx/wasm/HostFuncImplGetter.cpp
+++ b/src/libxrpl/tx/wasm/HostFuncImplGetter.cpp
@@ -15,7 +15,6 @@
 #include <cstdint>
 #include <expected>
 #include <stdexcept>
-#include <string>
 #include <utility>
 #include <variant>
 
@@ -124,9 +123,10 @@ getAnyFieldData(FieldValue const& variantObj)
     if (uint256 const* const* u = std::get_if<uint256 const*>(&variantObj))
         return Bytes((*u)->begin(), (*u)->end());
 
-    // Unreachable: the variant only holds the two alternatives above. If not,
-    // it's an xrpld bug -> tecINTERNAL (thrown, caught by HostFuncMain_wrap).
-    Throw<std::runtime_error>(std::string(hfErrInternal));  // LCOV_EXCL_LINE
+    // Unreachable: the variant only holds the two alternatives above. If not, it is an
+    // xrpld bug, and `guarded` turns the throw into the engine's fatal `Internal` ->
+    // tecINTERNAL.
+    Throw<std::runtime_error>("field value variant holds neither alternative");  // LCOV_EXCL_LINE
 }
 
 static inline bool
diff --git a/src/libxrpl/tx/wasm/HostFuncWrapper.cpp b/src/libxrpl/tx/wasm/HostFuncWrapper.cpp
deleted file mode 100644
index a6cd5fc1e3a..00000000000
--- a/src/libxrpl/tx/wasm/HostFuncWrapper.cpp
+++ /dev/null
@@ -1,1903 +0,0 @@
-#include <xrpl/tx/wasm/HostFuncWrapper.h>
-
-#include <xrpl/basics/Slice.h>
-#include <xrpl/basics/base_uint.h>
-#include <xrpl/basics/contract.h>
-#include <xrpl/beast/utility/Journal.h>
-#include <xrpl/protocol/AccountID.h>
-#include <xrpl/protocol/Asset.h>
-#include <xrpl/protocol/Issue.h>
-#include <xrpl/protocol/KeyType.h>
-#include <xrpl/protocol/Protocol.h>
-#include <xrpl/protocol/PublicKey.h>
-#include <xrpl/protocol/SField.h>
-#include <xrpl/protocol/STAmount.h>
-#include <xrpl/protocol/STNumber.h>
-#include <xrpl/protocol/SecretKey.h>
-#include <xrpl/protocol/Seed.h>
-#include <xrpl/protocol/Serializer.h>
-#include <xrpl/protocol/UintTypes.h>
-#include <xrpl/protocol/digest.h>
-#include <xrpl/tx/wasm/HostFunc.h>
-#include <xrpl/tx/wasm/WasmCommon.h>
-#include <xrpl/tx/wasm/WasmImportsHelper.h>
-#include <xrpl/tx/wasm/WasmVM.h>
-
-#include <boost/algorithm/hex.hpp>
-
-#include <wasm.h>
-
-#include <array>
-#include <cstddef>
-#include <cstdint>
-#include <cstring>
-#include <exception>
-#include <expected>
-#include <functional>
-#include <iterator>
-#include <optional>
-#include <stdexcept>
-#include <string>
-#include <string_view>
-#include <tuple>
-#include <type_traits>
-#include <utility>
-#include <vector>
-
-namespace xrpl {
-
-using SFieldCRef = std::reference_wrapper<SField const>;
-
-constexpr int64_t unalignedGas = 50;
-
-// Charge `delta` gas; returns the remaining gas. Out-of-gas throws hfErrOutOfGas
-// (-> tecOUT_OF_GAS); a failed setGas is an xrpld bug, throws hfErrInternal
-// (-> tecINTERNAL). HostFuncMain_wrap turns both into traps.
-static inline std::int64_t
-checkGas(WasmRuntimeWrapper& rt, int64_t delta)
-{
-    int64_t const gas = rt.getGas();
-    if (delta == 0)
-        return gas;
-
-    int64_t const x = gas >= delta ? gas - delta : 0;
-
-    if (rt.setGas(x) < 0)
-        Throw<std::runtime_error>(std::string(hfErrInternal));  // LCOV_EXCL_LINE
-
-    if (gas < delta)
-        Throw<std::runtime_error>(std::string(hfErrOutOfGas));
-
-    return x;
-}
-
-// Transfer limit is a separate soft budget: exceeding it is a normal guest-facing
-// return code, not a trap. Only a failed setTransferLimit (an xrpld bug) throws.
-static inline std::expected<std::int64_t, HostFunctionError>
-checkTransfer(WasmRuntimeWrapper& rt, int64_t delta)
-{
-    auto const transLimit = rt.getTransferLimit();
-    int64_t const x = transLimit >= delta ? transLimit - delta : 0;
-
-    if (rt.setTransferLimit(x) < 0)
-        Throw<std::runtime_error>(std::string(hfErrInternal));  // LCOV_EXCL_LINE
-
-    if (transLimit < delta)
-        return std::unexpected(HostFunctionError::OutOfTransferLimit);
-
-    return x;
-}
-
-// On any failure here a C++ exception is thrown; HostFuncMain_wrap's catch-all
-// turns it into tecINTERNAL. These conditions are all xrpld-side invariants.
-static std::tuple<HostFunctions&, WasmImportFunc const&>
-mainCheck(void* env, wasm_val_vec_t const* params, wasm_val_vec_t* results)
-{
-    if (env == nullptr)
-        Throw<std::runtime_error>(std::string(hfErrInternal));  // LCOV_EXCL_LINE
-
-    if (params == nullptr)
-        Throw<std::runtime_error>(std::string(hfErrInternal));  // LCOV_EXCL_LINE
-
-    if (results == nullptr)
-        Throw<std::runtime_error>(std::string(hfErrInternal));  // LCOV_EXCL_LINE
-
-    WasmUserData const* udata = reinterpret_cast<WasmUserData*>(env);
-    HostFunctions& hf = udata->first;
-    WasmRuntimeWrapper& rt = hf.getRT();
-    WasmImportFunc const& impFunc = udata->second;
-
-    // Charge the per-call gas. Throws (and terminates) if out of gas.
-    checkGas(rt, impFunc.gas);
-
-    return std::tie(hf, impFunc);
-}
-
-//----------------------------------------------------------------------------------------------------------------------
-
-static int32_t
-setData(
-    WasmRuntimeWrapper& runtime,
-    int32_t dst,
-    int32_t dstSize,
-    uint8_t const* src,
-    int32_t srcSize)
-{
-    if (srcSize == 0)
-        return 0;  // LCOV_EXCL_LINE
-
-    if (dst < 0 || dstSize < 0 || (src == nullptr) || srcSize < 0)
-        return hfErrorToInt(HostFunctionError::InvalidParams);
-
-    if (srcSize > kMaxWasmDataLength)
-        return hfErrorToInt(HostFunctionError::DataFieldTooLarge);
-
-    auto const memory = runtime.getMem();
-
-    // LCOV_EXCL_START
-    if (memory.s == 0u)
-        return hfErrorToInt(HostFunctionError::NoMemExported);
-    // LCOV_EXCL_STOP
-    if (std::cmp_greater((int64_t)dst + dstSize, memory.s))
-        return hfErrorToInt(HostFunctionError::PointerOutOfBounds);
-    if (srcSize > dstSize)
-        return hfErrorToInt(HostFunctionError::BufferTooSmall);
-
-    if (auto t = checkTransfer(runtime, srcSize); !t)
-        return hfErrorToInt(t.error());
-
-    memcpy(memory.p + dst, src, srcSize);
-
-    return srcSize;
-}
-
-static std::expected<Slice, HostFunctionError>
-getDataSlice(WasmRuntimeWrapper& runtime, wasm_val_vec_t const* params, int32_t& i)
-{
-    int64_t const ptr = params->data[i].of.i32;
-    int64_t const size = params->data[i + 1].of.i32;
-    i += 2;
-    if (ptr < 0 || size < 0)
-        return std::unexpected(HostFunctionError::InvalidParams);
-
-    if (size == 0)
-        return Slice();
-
-    if (size > kMaxWasmDataLength)
-        return std::unexpected(HostFunctionError::DataFieldTooLarge);
-
-    auto const memory = runtime.getMem();
-    // LCOV_EXCL_START
-    if (memory.s == 0u)
-        return std::unexpected(HostFunctionError::NoMemExported);
-    // LCOV_EXCL_STOP
-
-    if (std::cmp_greater(ptr + size, memory.s))
-        return std::unexpected(HostFunctionError::PointerOutOfBounds);
-
-    Slice const data(memory.p + ptr, size);
-    return data;
-}
-
-static std::expected<int32_t, HostFunctionError>
-getDataInt32(WasmRuntimeWrapper const&, wasm_val_vec_t const* params, int32_t& i)
-{
-    auto const result = params->data[i].of.i32;
-    i++;
-    return result;
-}
-
-static std::expected<int64_t, HostFunctionError>
-getDataInt64(WasmRuntimeWrapper const&, wasm_val_vec_t const* params, int32_t& i)
-{
-    auto const result = params->data[i].of.i64;
-    i++;
-    return result;
-}
-
-template <class T>
-static std::expected<T, HostFunctionError>
-getDataUnsigned(WasmRuntimeWrapper& runtime, wasm_val_vec_t const* params, int32_t& i)
-{
-    static_assert(std::is_unsigned_v<T>);
-    auto const r = getDataSlice(runtime, params, i);
-    if (!r)
-        return std::unexpected(r.error());
-    if (r->size() != sizeof(T))
-        return std::unexpected(HostFunctionError::InvalidParams);
-
-    T x;
-    auto const p = reinterpret_cast<uintptr_t>(r->data());
-    if (p & (alignof(T) - 1))  // unaligned
-    {
-        memcpy(&x, r->data(), sizeof(T));
-    }
-    else
-    {
-        x = *reinterpret_cast<T const*>(r->data());
-    }
-    x = adjustWasmEndianess(x);
-
-    return x;
-}
-
-static std::expected<uint32_t, HostFunctionError>
-getDataUInt32(WasmRuntimeWrapper& runtime, wasm_val_vec_t const* params, int32_t& i)
-{
-    return getDataUnsigned<uint32_t>(runtime, params, i);
-}
-
-static std::expected<uint64_t, HostFunctionError>
-getDataUInt64(WasmRuntimeWrapper& runtime, wasm_val_vec_t const* params, int32_t& i)
-{
-    return getDataUnsigned<uint64_t>(runtime, params, i);
-}
-
-static std::expected<SFieldCRef, HostFunctionError>
-getDataSField(WasmRuntimeWrapper& runtime, wasm_val_vec_t const* params, int32_t& i)
-{
-    auto const& m = SField::getKnownCodeToField();
-    auto const it = m.find(params->data[i].of.i32);
-    i++;
-    if (it == m.end())
-        return std::unexpected(HostFunctionError::InvalidField);
-
-    return *it->second;
-}
-
-static std::expected<uint256, HostFunctionError>
-getDataUInt256(WasmRuntimeWrapper& runtime, wasm_val_vec_t const* params, int32_t& i)
-{
-    auto const slice = getDataSlice(runtime, params, i);
-    if (!slice)
-        return std::unexpected(slice.error());
-
-    if (slice->size() != uint256::size())
-        return std::unexpected(HostFunctionError::InvalidParams);
-
-    if (auto t = checkTransfer(runtime, uint256::size()); !t)
-        return std::unexpected(t.error());
-
-    return uint256::fromVoid(slice->data());
-}
-
-static std::expected<AccountID, HostFunctionError>
-getDataAccountID(WasmRuntimeWrapper& runtime, wasm_val_vec_t const* params, int32_t& i)
-{
-    auto const slice = getDataSlice(runtime, params, i);
-    if (!slice)
-        return std::unexpected(slice.error());
-
-    if (slice->size() != AccountID::size())
-        return std::unexpected(HostFunctionError::InvalidParams);
-
-    if (auto t = checkTransfer(runtime, AccountID::size()); !t)
-        return std::unexpected(t.error());
-
-    return AccountID::fromVoid(slice->data());
-}
-
-static std::expected<Currency, HostFunctionError>
-getDataCurrency(WasmRuntimeWrapper& runtime, wasm_val_vec_t const* params, int32_t& i)
-{
-    auto const slice = getDataSlice(runtime, params, i);
-    if (!slice)
-        return std::unexpected(slice.error());
-
-    if (slice->size() != Currency::size())
-        return std::unexpected(HostFunctionError::InvalidParams);
-
-    if (auto t = checkTransfer(runtime, Currency::size()); !t)
-        return std::unexpected(t.error());
-
-    return Currency::fromVoid(slice->data());
-}
-
-static std::expected<Asset, HostFunctionError>
-getDataAsset(WasmRuntimeWrapper& runtime, wasm_val_vec_t const* params, int32_t& i)
-{
-    auto const slice = getDataSlice(runtime, params, i);
-    if (!slice)
-        return std::unexpected(slice.error());
-
-    if (slice->size() == MPTID::size())
-    {
-        if (auto t = checkTransfer(runtime, slice->size()); !t)
-            return std::unexpected(t.error());
-
-        auto const mptid = MPTID::fromVoid(slice->data());
-        return Asset{mptid};
-    }
-
-    if (slice->size() == Currency::size())
-    {
-        if (auto t = checkTransfer(runtime, slice->size()); !t)
-            return std::unexpected(t.error());
-
-        auto const currency = Currency::fromVoid(slice->data());
-        auto const issue = Issue{currency, xrpAccount()};
-        if (!issue.native())
-            return std::unexpected(HostFunctionError::InvalidParams);
-
-        return Asset{issue};
-    }
-
-    if (slice->size() == (Currency::size() + AccountID::size()))
-    {
-        if (auto t = checkTransfer(runtime, slice->size()); !t)
-            return std::unexpected(t.error());
-
-        auto const issue = Issue(
-            Currency::fromVoid(slice->data()),
-            AccountID::fromVoid(slice->data() + Currency::size()));
-
-        if (issue.native())
-            return std::unexpected(HostFunctionError::InvalidParams);
-
-        return Asset{issue};
-    }
-
-    return std::unexpected(HostFunctionError::InvalidParams);
-}
-
-static std::expected<std::string_view, HostFunctionError>
-getDataString(WasmRuntimeWrapper& runtime, wasm_val_vec_t const* params, int32_t& i)
-{
-    auto const slice = getDataSlice(runtime, params, i);
-    if (!slice)
-        return std::unexpected(slice.error());
-
-    return std::string_view(reinterpret_cast<char const*>(slice->data()), slice->size());
-}
-
-static std::expected<FieldLocator, HostFunctionError>
-getDataLocator(WasmRuntimeWrapper& runtime, wasm_val_vec_t const* params, int32_t& i)
-{
-    static_assert(kMaxWasmDataLength % sizeof(int32_t) == 0);
-
-    auto const slice = getDataSlice(runtime, params, i);
-    if (!slice)
-        return std::unexpected(slice.error());
-    if (slice->empty() || ((slice->size() & 3) != 0u))  // must be multiple of 4
-        return std::unexpected(HostFunctionError::LocatorMalformed);
-
-    uint32_t const locSize = slice->size() / sizeof(int32_t);
-    auto const p = reinterpret_cast<uintptr_t>(slice->data());
-
-    if ((p & (alignof(int32_t) - 1)) != 0u)
-    {  // unaligned
-
-        // Use gas and transfer limit for copying. checkGas throws (and
-        // terminates execution) if out of gas; checkTransfer keeps returning a
-        // guest-facing code when the transfer limit is exceeded.
-        checkGas(runtime, unalignedGas);
-        if (auto t = checkTransfer(runtime, slice->size()); !t)
-            return std::unexpected(t.error());
-
-        std::vector<int32_t> locBuf(locSize);
-        memcpy(&locBuf[0], slice->data(), slice->size());
-        FieldLocator locator(std::move(locBuf));
-
-        return locator;
-    }
-
-    auto const* locPtr = reinterpret_cast<int32_t const*>(slice->data());
-    return FieldLocator(locPtr, locSize);
-}
-
-static inline std::nullptr_t
-hfResult(wasm_val_vec_t* results, int32_t value)
-{
-    results->data[0] = WASM_I32_VAL(value);
-    // results->size = 1;
-    return nullptr;
-}
-
-static inline std::nullptr_t
-hfResult(wasm_val_vec_t* results, HostFunctionError value)
-{
-    results->data[0] = WASM_I32_VAL(hfErrorToInt(value));
-    // results->size = 1;
-    return nullptr;
-}
-
-template <typename T>
-static std::nullptr_t
-returnResult(
-    WasmRuntimeWrapper& runtime,
-    wasm_val_vec_t const* params,
-    wasm_val_vec_t* results,
-    std::expected<T, HostFunctionError> const& res,
-    int32_t index)
-{
-    if (!res)
-        return hfResult(results, res.error());
-
-    if constexpr (std::is_same_v<T, Bytes>)
-    {
-        if (index < 0 || index + 1 >= params->size)
-            Throw<std::runtime_error>(std::string(hfErrInternal));  // LCOV_EXCL_LINE
-
-        auto const dataResult = setData(
-            runtime,
-            params->data[index].of.i32,
-            params->data[index + 1].of.i32,
-            res->data(),
-            res->size());
-        return hfResult(results, dataResult);
-    }
-    else if constexpr (std::is_same_v<T, Hash>)
-    {
-        if (index < 0 || index + 1 >= params->size)
-            Throw<std::runtime_error>(std::string(hfErrInternal));  // LCOV_EXCL_LINE
-
-        auto const dataResult = setData(
-            runtime,
-            params->data[index].of.i32,
-            params->data[index + 1].of.i32,
-            res->data(),
-            res->size());
-        return hfResult(results, dataResult);
-    }
-    else if constexpr (std::is_same_v<T, int32_t>)
-    {
-        return hfResult(results, res.value());
-    }
-    else if constexpr (std::is_same_v<T, std::uint32_t>)
-    {
-        if (index < 0 || index + 1 >= params->size)
-            Throw<std::runtime_error>(std::string(hfErrInternal));  // LCOV_EXCL_LINE
-
-        auto const resultValue = adjustWasmEndianess(res.value());
-        auto const dataResult = setData(
-            runtime,
-            params->data[index].of.i32,
-            params->data[index + 1].of.i32,
-            reinterpret_cast<uint8_t const*>(&resultValue),
-            static_cast<int32_t>(sizeof(resultValue)));
-        return hfResult(results, dataResult);
-    }
-    else if constexpr (std::is_same_v<T, int64_t>)
-    {
-        if (index < 0 || index + 1 >= params->size)
-            Throw<std::runtime_error>(std::string(hfErrInternal));  // LCOV_EXCL_LINE
-
-        auto const resultValue = adjustWasmEndianess(res.value());
-        auto const dataResult = setData(
-            runtime,
-            params->data[index].of.i32,
-            params->data[index + 1].of.i32,
-            reinterpret_cast<uint8_t const*>(&resultValue),
-            static_cast<int32_t>(sizeof(resultValue)));
-        return hfResult(results, dataResult);
-    }
-    else if constexpr (std::is_same_v<T, FloatPair>)
-    {
-        if (index < 0 || index + 3 >= params->size)
-            Throw<std::runtime_error>(std::string(hfErrInternal));  // LCOV_EXCL_LINE
-
-        auto const mantissa = adjustWasmEndianess(res->first);
-        auto const r1 = setData(
-            runtime,
-            params->data[index].of.i32,
-            params->data[index + 1].of.i32,
-            reinterpret_cast<uint8_t const*>(&mantissa),
-            static_cast<int32_t>(sizeof(mantissa)));
-        if (r1 < 0)
-            return hfResult(results, r1);
-
-        index += 2;
-        auto const exponent = adjustWasmEndianess(res->second);
-        auto const r2 = setData(
-            runtime,
-            params->data[index].of.i32,
-            params->data[index + 1].of.i32,
-            reinterpret_cast<uint8_t const*>(&exponent),
-            static_cast<int32_t>(sizeof(exponent)));
-        if (r2 < 0)
-            return hfResult(results, r2);
-
-        return hfResult(results, r1 + r2);  // 12 bytes
-    }
-    else
-    {
-        static_assert([] { return false; }(), "Unhandled return type in returnResult");
-    }
-}
-
-//----------------------------------------------------------------------------------------------------------------------
-
-wasm_trap_t*
-HostFuncMain_wrap(WASM_CB_PARAMS_LIST)
-{
-    [[maybe_unused]] std::string_view hfName;
-
-    try
-    {
-        auto [hf, impFunc] = mainCheck(env, params, results);
-        hfName = impFunc.name;
-        auto* fWrap = reinterpret_cast<wasmSecondaryCbFuncType*>(impFunc.wrap);
-        return fWrap(hf, params, results);
-    }
-    catch (std::exception const& e)
-    {
-#ifdef DEBUG_OUTPUT
-        std::cerr << "Hostfunction " << hfName << " exception: " << e.what() << std::endl;
-#endif
-        // Normalize to the two boundary signals: explicit out-of-gas, else any
-        // exception (including stray ones from helpers) is an internal fault.
-        bool const oog = std::string_view(e.what()) == hfErrOutOfGas;
-        wasm_trap_t* trap = reinterpret_cast<wasm_trap_t*>(  // NOLINT
-            WasmEngine::instance().newTrap(std::string(oog ? hfErrOutOfGas : hfErrInternal)));
-        return trap;
-    }
-    catch (...)
-    {
-#ifdef DEBUG_OUTPUT
-        std::cerr << "Hostfunction " << hfName << " unknown exception." << std::endl;
-#endif
-        wasm_trap_t* trap = reinterpret_cast<wasm_trap_t*>(               // NOLINT
-            WasmEngine::instance().newTrap(std::string(hfErrInternal)));  // LCOV_EXCL_LINE
-        return trap;
-    }
-
-    return nullptr;  // LCOV_EXCL_LINE
-}
-
-//----------------------------------------------------------------------------------------------------------------------
-wasm_trap_t*
-getLedgerSqn_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t const index = 0;
-    auto& runtime = hf.getRT();
-
-    return returnResult(runtime, params, results, hf.getLedgerSqn(), index);
-}
-
-wasm_trap_t*
-getParentLedgerTime_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t const index = 0;
-    auto& runtime = hf.getRT();
-
-    return returnResult(runtime, params, results, hf.getParentLedgerTime(), index);
-}
-
-wasm_trap_t*
-getParentLedgerHash_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t const index = 0;
-    auto& runtime = hf.getRT();
-
-    return returnResult(runtime, params, results, hf.getParentLedgerHash(), index);
-}
-
-wasm_trap_t*
-getBaseFee_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t const index = 0;
-    auto& runtime = hf.getRT();
-
-    return returnResult(runtime, params, results, hf.getBaseFee(), index);
-}
-
-wasm_trap_t*
-isAmendmentEnabled_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const slice = getDataSlice(runtime, params, index);
-    if (!slice)
-        return hfResult(results, slice.error());
-
-    if (slice->size() == uint256::size())
-    {
-        if (auto const ret = hf.isAmendmentEnabled(uint256::fromVoid(slice->data()));
-            ret && *ret == 1)
-            return returnResult(runtime, params, results, ret, index);
-        // Fall through to string lookup — the 32 bytes may be an amendment name
-    }
-
-    if (slice->size() > 64)
-        return hfResult(results, HostFunctionError::DataFieldTooLarge);
-
-    auto const str = std::string_view(reinterpret_cast<char const*>(slice->data()), slice->size());
-    return returnResult(runtime, params, results, hf.isAmendmentEnabled(str), index);
-}
-
-wasm_trap_t*
-cacheLedgerObj_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const id = getDataUInt256(runtime, params, index);
-    if (!id)
-        return hfResult(results, id.error());
-
-    auto const cache = getDataInt32(runtime, params, index);
-    if (!cache)
-        return hfResult(results, cache.error());  // LCOV_EXCL_LINE
-
-    return returnResult(runtime, params, results, hf.cacheLedgerObj(*id, *cache), index);
-}
-
-wasm_trap_t*
-getTxField_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const fname = getDataSField(runtime, params, index);
-    if (!fname)
-        return hfResult(results, fname.error());
-
-    return returnResult(runtime, params, results, hf.getTxField(*fname), index);
-}
-
-wasm_trap_t*
-getCurrentLedgerObjField_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const fname = getDataSField(runtime, params, index);
-    if (!fname)
-        return hfResult(results, fname.error());
-
-    return returnResult(runtime, params, results, hf.getCurrentLedgerObjField(*fname), index);
-}
-
-wasm_trap_t*
-getLedgerObjField_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const cache = getDataInt32(runtime, params, index);
-    if (!cache)
-        return hfResult(results, cache.error());  // LCOV_EXCL_LINE
-
-    auto const fname = getDataSField(runtime, params, index);
-    if (!fname)
-        return hfResult(results, fname.error());
-
-    return returnResult(runtime, params, results, hf.getLedgerObjField(*cache, *fname), index);
-}
-
-wasm_trap_t*
-getTxNestedField_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const locator = getDataLocator(runtime, params, index);
-    if (!locator)
-        return hfResult(results, locator.error());
-
-    return returnResult(runtime, params, results, hf.getTxNestedField(*locator), index);
-}
-
-wasm_trap_t*
-getCurrentLedgerObjNestedField_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const locator = getDataLocator(runtime, params, index);
-    if (!locator)
-        return hfResult(results, locator.error());
-
-    return returnResult(
-        runtime, params, results, hf.getCurrentLedgerObjNestedField(*locator), index);
-}
-
-wasm_trap_t*
-getLedgerObjNestedField_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const cache = getDataInt32(runtime, params, index);
-    if (!cache)
-        return hfResult(results, cache.error());  // LCOV_EXCL_LINE
-
-    auto const locator = getDataLocator(runtime, params, index);
-    if (!locator)
-        return hfResult(results, locator.error());
-
-    return returnResult(
-        runtime, params, results, hf.getLedgerObjNestedField(*cache, *locator), index);
-}
-
-wasm_trap_t*
-getTxArrayLen_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const fname = getDataSField(runtime, params, index);
-    if (!fname)
-        return hfResult(results, fname.error());
-
-    return returnResult(runtime, params, results, hf.getTxArrayLen(*fname), index);
-}
-
-wasm_trap_t*
-getCurrentLedgerObjArrayLen_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const fname = getDataSField(runtime, params, index);
-    if (!fname)
-        return hfResult(results, fname.error());
-
-    return returnResult(runtime, params, results, hf.getCurrentLedgerObjArrayLen(*fname), index);
-}
-
-wasm_trap_t*
-getLedgerObjArrayLen_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const cache = getDataInt32(runtime, params, index);
-    if (!cache)
-        return hfResult(results, cache.error());  // LCOV_EXCL_LINE
-
-    auto const fname = getDataSField(runtime, params, index);
-    if (!fname)
-        return hfResult(results, fname.error());
-
-    return returnResult(runtime, params, results, hf.getLedgerObjArrayLen(*cache, *fname), index);
-}
-
-wasm_trap_t*
-getTxNestedArrayLen_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const locator = getDataLocator(runtime, params, index);
-    if (!locator)
-        return hfResult(results, locator.error());
-
-    return returnResult(runtime, params, results, hf.getTxNestedArrayLen(*locator), index);
-}
-
-wasm_trap_t*
-getCurrentLedgerObjNestedArrayLen_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const locator = getDataLocator(runtime, params, index);
-    if (!locator)
-        return hfResult(results, locator.error());
-
-    return returnResult(
-        runtime, params, results, hf.getCurrentLedgerObjNestedArrayLen(*locator), index);
-}
-wasm_trap_t*
-getLedgerObjNestedArrayLen_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const cache = getDataInt32(runtime, params, index);
-    if (!cache)
-        return hfResult(results, cache.error());  // LCOV_EXCL_LINE
-
-    auto const locator = getDataLocator(runtime, params, index);
-    if (!locator)
-        return hfResult(results, locator.error());
-
-    return returnResult(
-        runtime, params, results, hf.getLedgerObjNestedArrayLen(*cache, *locator), index);
-}
-
-wasm_trap_t*
-updateData_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const bytes = getDataSlice(runtime, params, index);
-    if (!bytes)
-        return hfResult(results, bytes.error());
-
-    return returnResult(runtime, params, results, hf.updateData(*bytes), index);
-}
-
-wasm_trap_t*
-checkSignature_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const message = getDataSlice(runtime, params, index);
-    if (!message)
-        return hfResult(results, message.error());
-
-    auto const signature = getDataSlice(runtime, params, index);
-    if (!signature)
-        return hfResult(results, signature.error());
-
-    auto const pubkey = getDataSlice(runtime, params, index);
-    if (!pubkey)
-        return hfResult(results, pubkey.error());
-
-    return returnResult(
-        runtime, params, results, hf.checkSignature(*message, *signature, *pubkey), index);
-}
-
-wasm_trap_t*
-computeSha512HalfHash_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const bytes = getDataSlice(runtime, params, index);
-    if (!bytes)
-        return hfResult(results, bytes.error());
-
-    return returnResult(runtime, params, results, hf.computeSha512HalfHash(*bytes), index);
-}
-
-wasm_trap_t*
-accountKeylet_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const acc = getDataAccountID(runtime, params, index);
-    if (!acc)
-        return hfResult(results, acc.error());
-
-    return returnResult(runtime, params, results, hf.accountKeylet(*acc), index);
-}
-
-wasm_trap_t*
-ammKeylet_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const issue1 = getDataAsset(runtime, params, index);
-    if (!issue1)
-        return hfResult(results, issue1.error());
-
-    auto const issue2 = getDataAsset(runtime, params, index);
-    if (!issue2)
-        return hfResult(results, issue2.error());
-
-    return returnResult(
-        runtime, params, results, hf.ammKeylet(issue1.value(), issue2.value()), index);
-}
-
-wasm_trap_t*
-checkKeylet_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const acc = getDataAccountID(runtime, params, index);
-    if (!acc)
-        return hfResult(results, acc.error());
-
-    auto const seq = getDataUInt32(runtime, params, index);
-    if (!seq)
-        return hfResult(results, seq.error());
-
-    return returnResult(runtime, params, results, hf.checkKeylet(acc.value(), *seq), index);
-}
-
-wasm_trap_t*
-credentialKeylet_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const subj = getDataAccountID(runtime, params, index);
-    if (!subj)
-        return hfResult(results, subj.error());
-
-    auto const iss = getDataAccountID(runtime, params, index);
-    if (!iss)
-        return hfResult(results, iss.error());
-
-    auto const credType = getDataSlice(runtime, params, index);
-    if (!credType)
-        return hfResult(results, credType.error());
-
-    return returnResult(
-        runtime, params, results, hf.credentialKeylet(*subj, *iss, *credType), index);
-}
-
-wasm_trap_t*
-delegateKeylet_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const acc = getDataAccountID(runtime, params, index);
-    if (!acc)
-        return hfResult(results, acc.error());
-
-    auto const authorize = getDataAccountID(runtime, params, index);
-    if (!authorize)
-        return hfResult(results, authorize.error());
-
-    return returnResult(
-        runtime, params, results, hf.delegateKeylet(acc.value(), authorize.value()), index);
-}
-
-wasm_trap_t*
-depositPreauthKeylet_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const acc = getDataAccountID(runtime, params, index);
-    if (!acc)
-        return hfResult(results, acc.error());
-
-    auto const authorize = getDataAccountID(runtime, params, index);
-    if (!authorize)
-        return hfResult(results, authorize.error());
-
-    return returnResult(
-        runtime, params, results, hf.depositPreauthKeylet(acc.value(), authorize.value()), index);
-}
-
-wasm_trap_t*
-didKeylet_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const acc = getDataAccountID(runtime, params, index);
-    if (!acc)
-        return hfResult(results, acc.error());
-
-    return returnResult(runtime, params, results, hf.didKeylet(acc.value()), index);
-}
-
-wasm_trap_t*
-escrowKeylet_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const acc = getDataAccountID(runtime, params, index);
-    if (!acc)
-        return hfResult(results, acc.error());
-
-    auto const seq = getDataUInt32(runtime, params, index);
-    if (!seq)
-        return hfResult(results, seq.error());
-
-    return returnResult(runtime, params, results, hf.escrowKeylet(*acc, *seq), index);
-}
-
-wasm_trap_t*
-trustLineKeylet_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const acc1 = getDataAccountID(runtime, params, index);
-    if (!acc1)
-        return hfResult(results, acc1.error());
-
-    auto const acc2 = getDataAccountID(runtime, params, index);
-    if (!acc2)
-        return hfResult(results, acc2.error());
-
-    auto const currency = getDataCurrency(runtime, params, index);
-    if (!currency)
-        return hfResult(results, currency.error());
-
-    return returnResult(
-        runtime,
-        params,
-        results,
-        hf.trustLineKeylet(acc1.value(), acc2.value(), currency.value()),
-        index);
-}
-
-wasm_trap_t*
-mptokenIssuanceKeylet_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const acc = getDataAccountID(runtime, params, index);
-    if (!acc)
-        return hfResult(results, acc.error());
-
-    auto const seq = getDataUInt32(runtime, params, index);
-    if (!seq)
-        return hfResult(results, seq.error());
-
-    return returnResult(
-        runtime, params, results, hf.mptokenIssuanceKeylet(acc.value(), seq.value()), index);
-}
-
-wasm_trap_t*
-mptokenKeylet_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const slice = getDataSlice(runtime, params, index);
-    if (!slice)
-        return hfResult(results, slice.error());
-
-    if (slice->size() != MPTID::size())
-        return hfResult(results, HostFunctionError::InvalidParams);
-    auto const mptid = MPTID::fromVoid(slice->data());
-
-    auto const holder = getDataAccountID(runtime, params, index);
-    if (!holder)
-        return hfResult(results, holder.error());
-
-    return returnResult(runtime, params, results, hf.mptokenKeylet(mptid, holder.value()), index);
-}
-
-wasm_trap_t*
-nftokenOfferKeylet_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const acc = getDataAccountID(runtime, params, index);
-    if (!acc)
-        return hfResult(results, acc.error());
-
-    auto const seq = getDataUInt32(runtime, params, index);
-    if (!seq)
-        return hfResult(results, seq.error());
-
-    return returnResult(
-        runtime, params, results, hf.nftokenOfferKeylet(acc.value(), seq.value()), index);
-}
-
-wasm_trap_t*
-offerKeylet_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const acc = getDataAccountID(runtime, params, index);
-    if (!acc)
-        return hfResult(results, acc.error());
-
-    auto const seq = getDataUInt32(runtime, params, index);
-    if (!seq)
-        return hfResult(results, seq.error());
-
-    return returnResult(runtime, params, results, hf.offerKeylet(acc.value(), seq.value()), index);
-}
-
-wasm_trap_t*
-oracleKeylet_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const acc = getDataAccountID(runtime, params, index);
-    if (!acc)
-        return hfResult(results, acc.error());
-
-    auto const documentId = getDataUInt32(runtime, params, index);
-    if (!documentId)
-        return hfResult(results, documentId.error());
-
-    return returnResult(runtime, params, results, hf.oracleKeylet(*acc, *documentId), index);
-}
-
-wasm_trap_t*
-paychannelKeylet_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const acc = getDataAccountID(runtime, params, index);
-    if (!acc)
-        return hfResult(results, acc.error());
-
-    auto const dest = getDataAccountID(runtime, params, index);
-    if (!dest)
-        return hfResult(results, dest.error());
-
-    auto const seq = getDataUInt32(runtime, params, index);
-    if (!seq)
-        return hfResult(results, seq.error());
-
-    return returnResult(
-        runtime,
-        params,
-        results,
-        hf.paychannelKeylet(acc.value(), dest.value(), seq.value()),
-        index);
-}
-
-wasm_trap_t*
-permissionedDomainKeylet_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const acc = getDataAccountID(runtime, params, index);
-    if (!acc)
-        return hfResult(results, acc.error());
-
-    auto const seq = getDataUInt32(runtime, params, index);
-    if (!seq)
-        return hfResult(results, seq.error());
-
-    return returnResult(
-        runtime, params, results, hf.permissionedDomainKeylet(acc.value(), seq.value()), index);
-}
-
-wasm_trap_t*
-signerListKeylet_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const acc = getDataAccountID(runtime, params, index);
-    if (!acc)
-        return hfResult(results, acc.error());
-
-    return returnResult(runtime, params, results, hf.signerListKeylet(acc.value()), index);
-}
-
-wasm_trap_t*
-ticketKeylet_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const acc = getDataAccountID(runtime, params, index);
-    if (!acc)
-        return hfResult(results, acc.error());
-
-    auto const seq = getDataUInt32(runtime, params, index);
-    if (!seq)
-        return hfResult(results, seq.error());
-
-    return returnResult(runtime, params, results, hf.ticketKeylet(acc.value(), seq.value()), index);
-}
-
-wasm_trap_t*
-vaultKeylet_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const acc = getDataAccountID(runtime, params, index);
-    if (!acc)
-        return hfResult(results, acc.error());
-
-    auto const seq = getDataUInt32(runtime, params, index);
-    if (!seq)
-        return hfResult(results, seq.error());
-
-    return returnResult(runtime, params, results, hf.vaultKeylet(acc.value(), seq.value()), index);
-}
-
-wasm_trap_t*
-getNFT_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const acc = getDataAccountID(runtime, params, index);
-    if (!acc)
-        return hfResult(results, acc.error());
-
-    auto const nftId = getDataUInt256(runtime, params, index);
-    if (!nftId)
-        return hfResult(results, nftId.error());
-
-    return returnResult(runtime, params, results, hf.getNFT(*acc, *nftId), index);
-}
-
-wasm_trap_t*
-getNFTIssuer_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const nftId = getDataUInt256(runtime, params, index);
-    if (!nftId)
-        return hfResult(results, nftId.error());
-
-    return returnResult(runtime, params, results, hf.getNFTIssuer(*nftId), index);
-}
-
-wasm_trap_t*
-getNFTTaxon_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const nftId = getDataUInt256(runtime, params, index);
-    if (!nftId)
-        return hfResult(results, nftId.error());
-
-    return returnResult(runtime, params, results, hf.getNFTTaxon(*nftId), index);
-}
-
-wasm_trap_t*
-getNFTFlags_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const nftId = getDataUInt256(runtime, params, index);
-    if (!nftId)
-        return hfResult(results, nftId.error());
-
-    return returnResult(runtime, params, results, hf.getNFTFlags(*nftId), index);
-}
-
-wasm_trap_t*
-getNFTTransferFee_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const nftId = getDataUInt256(runtime, params, index);
-    if (!nftId)
-        return hfResult(results, nftId.error());
-
-    return returnResult(runtime, params, results, hf.getNFTTransferFee(*nftId), index);
-}
-
-wasm_trap_t*
-getNFTSequence_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t index = 0;
-    auto& runtime = hf.getRT();
-
-    auto const nftId = getDataUInt256(runtime, params, index);
-    if (!nftId)
-        return hfResult(results, nftId.error());
-
-    return returnResult(runtime, params, results, hf.getNFTSequence(*nftId), index);
-}
-
-// log() ignores the journal under DEBUG_OUTPUT, so the gate must not either.
-static inline bool
-traceActive([[maybe_unused]] HostFunctions const& hf)
-{
-#ifdef DEBUG_OUTPUT
-    return true;
-#else
-    return hf.getJournal().active(beast::Severity::Trace);
-#endif
-}
-
-// Not getDataUnsigned: that branches on pointer alignment, and trace must cost
-// the same regardless of how the guest laid out its buffer.
-template <class T>
-static std::optional<T>
-traceInt(Slice const& data)
-{
-    static_assert(std::is_integral_v<T>);
-    if (data.size() != sizeof(T))
-        return std::nullopt;
-
-    T x;
-    memcpy(&x, data.data(), sizeof(T));
-    return adjustWasmEndianess(x);
-}
-
-// std::nullopt means the buffer does not match the type. May throw.
-static std::optional<std::string>
-traceFormat(TraceDataType type, Slice const& data)
-{
-    switch (type)
-    {
-        case TraceDataType::Int64:
-            if (auto const x = traceInt<std::int64_t>(data))
-                return std::to_string(*x);
-            return std::nullopt;
-
-        case TraceDataType::Uint64:
-            if (auto const x = traceInt<std::uint64_t>(data))
-                return std::to_string(*x);
-            return std::nullopt;
-
-        case TraceDataType::Xfloat:
-            return wasm_float::floatToString(data);
-
-        case TraceDataType::Account:
-            // Not getDataAccountID: it charges the transfer limit.
-            if (data.size() != AccountID::size())
-                return std::nullopt;
-            return toBase58(AccountID::fromVoid(data.data()));
-
-        case TraceDataType::Amount: {
-            auto serialIter = SerialIter(data);
-            STAmount const amount(serialIter, sfGeneric);  // may throw
-            return amount.getFullText();
-        }
-
-        case TraceDataType::AsHex: {
-            std::string hex;
-            hex.reserve(data.size() * 2);
-            boost::algorithm::hex(data.begin(), data.end(), std::back_inserter(hex));
-            return hex;
-        }
-
-        case TraceDataType::AsText:
-            // An empty Slice has a null data(), which std::string may not take.
-            if (data.empty())
-                return std::string();
-            return std::string(reinterpret_cast<char const*>(data.data()), data.size());
-    }
-
-    return std::nullopt;  // unknown data_type
-}
-
-// trace's only effect is this node's local log, so nothing observable may depend
-// on the log level: gas is charged in mainCheck before this runs, no transfer
-// limit is charged, and errors are logged rather than trapped.
-wasm_trap_t*
-trace_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    if (!traceActive(hf))
-        return nullptr;
-
-    try
-    {
-        int32_t index = 0;
-        auto& runtime = hf.getRT();
-
-        auto const msg = getDataString(runtime, params, index);
-        if (!msg)
-        {
-            hf.getJournal().trace() << "WasmTrace: invalid message";
-            return nullptr;
-        }
-
-        auto const type = getDataInt32(runtime, params, index);
-        // LCOV_EXCL_START
-        if (!type)
-        {
-            hf.getJournal().trace() << "WasmTrace: invalid data type";
-            return nullptr;
-        }
-        // LCOV_EXCL_STOP
-
-        auto const data = getDataSlice(runtime, params, index);
-        if (!data)
-        {
-            hf.getJournal().trace() << "WasmTrace: invalid data";
-            return nullptr;
-        }
-
-        if (msg->size() + data->size() > kMaxWasmDataLength)
-        {
-            hf.getJournal().trace() << "WasmTrace: message and data too long";
-            return nullptr;
-        }
-
-        auto const text = traceFormat(static_cast<TraceDataType>(*type), *data);
-        if (!text)
-        {
-            hf.getJournal().trace() << "WasmTrace: data does not match the data type";
-            return nullptr;
-        }
-
-        hf.trace(*msg, *text);
-    }
-    catch (std::exception const& e)
-    {
-        hf.getJournal().trace() << "WasmTrace: error: " << e.what();
-    }
-    // LCOV_EXCL_START
-    catch (...)
-    {
-        hf.getJournal().trace() << "WasmTrace: unknown error";
-    }
-    // LCOV_EXCL_STOP
-    return nullptr;
-}
-
-wasm_trap_t*
-floatFromInt_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t i = 0;
-    auto& runtime = hf.getRT();
-
-    auto const x = getDataInt64(runtime, params, i);
-    if (!x)
-        return hfResult(results, x.error());  // LCOV_EXCL_LINE
-
-    i = 3;
-    auto const rounding = getDataInt32(runtime, params, i);
-    if (!rounding)
-        return hfResult(results, rounding.error());  // LCOV_EXCL_LINE
-
-    i = 1;
-    return returnResult(runtime, params, results, hf.floatFromInt(*x, *rounding), i);
-}
-
-wasm_trap_t*
-floatFromUint_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t i = 0;
-    auto& runtime = hf.getRT();
-
-    auto const x = getDataUInt64(runtime, params, i);
-    if (!x)
-        return hfResult(results, x.error());
-
-    i = 4;
-    auto const rounding = getDataInt32(runtime, params, i);
-    if (!rounding)
-        return hfResult(results, rounding.error());  // LCOV_EXCL_LINE
-
-    i = 2;
-    return returnResult(runtime, params, results, hf.floatFromUint(*x, *rounding), i);
-}
-
-wasm_trap_t*
-floatFromSTAmount_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t i = 0;
-    auto& runtime = hf.getRT();
-
-    auto const x = getDataSlice(runtime, params, i);
-    if (!x)
-        return hfResult(results, x.error());
-
-    auto serialIter = SerialIter(*x);
-    std::optional<STAmount> amount;
-    try
-    {
-        amount = STAmount(serialIter, sfGeneric);
-    }
-    catch (std::exception const&)
-    {
-        amount = std::nullopt;
-    }
-    if (!amount)
-        return hfResult(results, HostFunctionError::InvalidParams);
-
-    i = 4;
-    auto const rounding = getDataInt32(runtime, params, i);
-    if (!rounding)
-        return hfResult(results, rounding.error());  // LCOV_EXCL_LINE
-
-    i = 2;
-    return returnResult(runtime, params, results, hf.floatFromSTAmount(*amount, *rounding), i);
-}
-
-wasm_trap_t*
-floatFromSTNumber_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t i = 0;
-    auto& runtime = hf.getRT();
-
-    auto const x = getDataSlice(runtime, params, i);
-    if (!x)
-        return hfResult(results, x.error());
-
-    auto serialIter = SerialIter(*x);
-    std::optional<STNumber> num;
-    try
-    {
-        num = STNumber(serialIter, sfGeneric);
-    }
-    catch (std::exception const&)
-    {
-        num = std::nullopt;
-    }
-    if (!num)
-        return hfResult(results, HostFunctionError::InvalidParams);
-
-    i = 4;
-    auto const rounding = getDataInt32(runtime, params, i);
-    if (!rounding)
-        return hfResult(results, rounding.error());  // LCOV_EXCL_LINE
-
-    i = 2;
-    return returnResult(runtime, params, results, hf.floatFromSTNumber(*num, *rounding), i);
-}
-
-wasm_trap_t*
-floatToInt_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t i = 0;
-    auto& runtime = hf.getRT();
-
-    auto const x = getDataSlice(runtime, params, i);
-    if (!x)
-        return hfResult(results, x.error());
-
-    i = 4;
-    auto const rounding = getDataInt32(runtime, params, i);
-    if (!rounding)
-        return hfResult(results, rounding.error());  // LCOV_EXCL_LINE
-
-    i = 2;
-    return returnResult(runtime, params, results, hf.floatToInt(*x, *rounding), i);
-}
-
-wasm_trap_t*
-floatToMantExp_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t i = 0;
-    auto& runtime = hf.getRT();
-
-    auto const x = getDataSlice(runtime, params, i);
-    if (!x)
-        return hfResult(results, x.error());
-
-    i = 2;
-    return returnResult(runtime, params, results, hf.floatToMantExp(*x), i);
-}
-
-wasm_trap_t*
-floatFromMantExp_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t i = 0;
-    auto& runtime = hf.getRT();
-
-    auto const mant = getDataInt64(runtime, params, i);
-    if (!mant)
-        return hfResult(results, mant.error());  // LCOV_EXCL_LINE
-
-    auto const exp = getDataInt32(runtime, params, i);
-    if (!exp)
-        return hfResult(results, exp.error());  // LCOV_EXCL_LINE
-
-    i = 4;
-    auto const rounding = getDataInt32(runtime, params, i);
-    if (!rounding)
-        return hfResult(results, rounding.error());  // LCOV_EXCL_LINE
-
-    i = 2;
-    return returnResult(runtime, params, results, hf.floatFromMantExp(*mant, *exp, *rounding), i);
-}
-
-wasm_trap_t*
-floatCompare_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t i = 0;
-    auto& runtime = hf.getRT();
-
-    auto const x = getDataSlice(runtime, params, i);
-    if (!x)
-        return hfResult(results, x.error());
-
-    auto const y = getDataSlice(runtime, params, i);
-    if (!y)
-        return hfResult(results, y.error());
-
-    return returnResult(runtime, params, results, hf.floatCompare(*x, *y), i);
-}
-
-wasm_trap_t*
-floatAdd_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t i = 0;
-    auto& runtime = hf.getRT();
-
-    auto const x = getDataSlice(runtime, params, i);
-    if (!x)
-        return hfResult(results, x.error());
-
-    auto const y = getDataSlice(runtime, params, i);
-    if (!y)
-        return hfResult(results, y.error());
-
-    i = 6;
-    auto const rounding = getDataInt32(runtime, params, i);
-    if (!rounding)
-        return hfResult(results, rounding.error());  // LCOV_EXCL_LINE
-
-    i = 4;
-    return returnResult(runtime, params, results, hf.floatAdd(*x, *y, *rounding), i);
-}
-
-wasm_trap_t*
-floatSubtract_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t i = 0;
-    auto& runtime = hf.getRT();
-
-    auto const x = getDataSlice(runtime, params, i);
-    if (!x)
-        return hfResult(results, x.error());
-
-    auto const y = getDataSlice(runtime, params, i);
-    if (!y)
-        return hfResult(results, y.error());
-
-    i = 6;
-    auto const rounding = getDataInt32(runtime, params, i);
-    if (!rounding)
-        return hfResult(results, rounding.error());  // LCOV_EXCL_LINE
-
-    i = 4;
-    return returnResult(runtime, params, results, hf.floatSubtract(*x, *y, *rounding), i);
-}
-
-wasm_trap_t*
-floatMultiply_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t i = 0;
-    auto& runtime = hf.getRT();
-
-    auto const x = getDataSlice(runtime, params, i);
-    if (!x)
-        return hfResult(results, x.error());
-
-    auto const y = getDataSlice(runtime, params, i);
-    if (!y)
-        return hfResult(results, y.error());
-
-    i = 6;
-    auto const rounding = getDataInt32(runtime, params, i);
-    if (!rounding)
-        return hfResult(results, rounding.error());  // LCOV_EXCL_LINE
-
-    i = 4;
-    return returnResult(runtime, params, results, hf.floatMultiply(*x, *y, *rounding), i);
-}
-
-wasm_trap_t*
-floatDivide_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t i = 0;
-    auto& runtime = hf.getRT();
-
-    auto const x = getDataSlice(runtime, params, i);
-    if (!x)
-        return hfResult(results, x.error());
-
-    auto const y = getDataSlice(runtime, params, i);
-    if (!y)
-        return hfResult(results, y.error());
-
-    i = 6;
-    auto const rounding = getDataInt32(runtime, params, i);
-    if (!rounding)
-        return hfResult(results, rounding.error());  // LCOV_EXCL_LINE
-
-    i = 4;
-    return returnResult(runtime, params, results, hf.floatDivide(*x, *y, *rounding), i);
-}
-
-wasm_trap_t*
-floatRoot_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t i = 0;
-    auto& runtime = hf.getRT();
-
-    auto const x = getDataSlice(runtime, params, i);
-    if (!x)
-        return hfResult(results, x.error());
-
-    auto const n = getDataInt32(runtime, params, i);
-    if (!n)
-        return hfResult(results, n.error());  // LCOV_EXCL_LINE
-
-    i = 5;
-    auto const rounding = getDataInt32(runtime, params, i);
-    if (!rounding)
-        return hfResult(results, rounding.error());  // LCOV_EXCL_LINE
-
-    i = 3;
-    return returnResult(runtime, params, results, hf.floatRoot(*x, *n, *rounding), i);
-}
-
-wasm_trap_t*
-floatPower_wrap(WASM_SECONDARY_CB_PARAMS_LIST)
-{
-    int32_t i = 0;
-    auto& runtime = hf.getRT();
-
-    auto const x = getDataSlice(runtime, params, i);
-    if (!x)
-        return hfResult(results, x.error());
-
-    auto const n = getDataInt32(runtime, params, i);
-    if (!n)
-        return hfResult(results, n.error());  // LCOV_EXCL_LINE
-
-    i = 5;
-    auto const rounding = getDataInt32(runtime, params, i);
-    if (!rounding)
-        return hfResult(results, rounding.error());  // LCOV_EXCL_LINE
-
-    i = 3;
-    return returnResult(runtime, params, results, hf.floatPower(*x, *n, *rounding), i);
-}
-
-// LCOV_EXCL_START
-namespace test {
-
-class MockWasmRuntimeWrapper : public WasmRuntimeWrapper
-{
-    Wmem mem_;
-
-    std::int64_t gas_ = 1'000'000;
-    std::int64_t transferLimit_ = kWasmTransferLimit;
-
-public:
-    MockWasmRuntimeWrapper(Wmem memory) : mem_(memory)
-    {
-    }
-
-    // Mock methods to simulate the behavior of WasmRuntimeWrapper
-    [[nodiscard]] Wmem
-    getMem() override
-    {
-        return mem_;
-    }
-
-    std::int64_t
-    getGas() override
-    {
-        return gas_;
-    }
-
-    std::int64_t
-    setGas(std::int64_t gas) override
-    {
-        gas_ = gas;
-        return gas_;
-    }
-
-    std::int64_t
-    getTransferLimit() override
-    {
-        return transferLimit_;
-    }
-
-    std::int64_t
-    setTransferLimit(std::int64_t x) override
-    {
-        transferLimit_ = x;
-        return transferLimit_;
-    }
-};
-
-bool
-testGetDataIncrement()
-{
-    wasm_val_t values[4];
-
-    std::array<std::uint8_t, 128> buffer = {'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h'};
-    MockWasmRuntimeWrapper runtime(Wmem(buffer.data(), buffer.size()));
-
-    {
-        // test int32_t
-        wasm_val_vec_t const params = {.size = 1, .data = &values[0]};
-
-        values[0] = WASM_I32_VAL(42);
-
-        int32_t index = 0;
-        auto const result = getDataInt32(runtime, &params, index);
-        if (!result || result.value() != 42 || index != 1)
-            return false;
-    }
-
-    {
-        // test int64_t
-        wasm_val_vec_t const params = {.size = 1, .data = &values[0]};
-
-        values[0] = WASM_I64_VAL(1234);
-
-        int32_t index = 0;
-        auto const result = getDataInt64(runtime, &params, index);
-        if (!result || result.value() != 1234 || index != 1)
-            return false;
-    }
-
-    {
-        // test SFieldCRef
-        wasm_val_vec_t const params = {.size = 1, .data = &values[0]};
-
-        values[0] = WASM_I32_VAL(sfAccount.getCode());
-
-        int32_t index = 0;
-        auto const result = getDataSField(runtime, &params, index);
-        if (!result || result.value().get() != sfAccount || index != 1)
-            return false;
-    }
-
-    {
-        // test Slice
-        wasm_val_vec_t const params = {.size = 2, .data = &values[0]};
-
-        values[0] = WASM_I32_VAL(0);
-        values[1] = WASM_I32_VAL(3);
-
-        int32_t index = 0;
-        auto const result = getDataSlice(runtime, &params, index);
-        if (!result || result.value() != Slice(buffer.data(), 3) || index != 2)
-            return false;
-    }
-
-    {
-        // test string
-        wasm_val_vec_t const params = {.size = 2, .data = &values[0]};
-
-        values[0] = WASM_I32_VAL(0);
-        values[1] = WASM_I32_VAL(5);
-
-        int32_t index = 0;
-        auto const result = getDataString(runtime, &params, index);
-        if (!result ||
-            result.value() != std::string_view(reinterpret_cast<char const*>(buffer.data()), 5) ||
-            index != 2)
-            return false;
-    }
-
-    {
-        // test account
-        AccountID const id(
-            calcAccountID(generateKeyPair(KeyType::Secp256k1, generateSeed("alice")).first));
-
-        wasm_val_vec_t const params = {.size = 2, .data = &values[0]};
-
-        values[0] = WASM_I32_VAL(0);
-        values[1] = WASM_I32_VAL(AccountID::size());
-        memcpy(&buffer[0], id.data(), AccountID::size());
-
-        int32_t index = 0;
-        auto const result = getDataAccountID(runtime, &params, index);
-        if (!result || result.value() != id || index != 2)
-            return false;
-    }
-
-    {
-        // test uint256
-
-        Hash h1 = sha512Half(Slice(buffer.data(), 8));
-        wasm_val_vec_t const params = {.size = 2, .data = &values[0]};
-
-        values[0] = WASM_I32_VAL(0);
-        values[1] = WASM_I32_VAL(Hash::size());
-        memcpy(&buffer[0], h1.data(), Hash::size());
-
-        int32_t index = 0;
-        auto const result = getDataUInt256(runtime, &params, index);
-        if (!result || result.value() != h1 || index != 2)
-            return false;
-    }
-
-    {
-        // test Currency
-
-        Currency const c = xrpCurrency();
-        wasm_val_vec_t const params = {.size = 2, .data = &values[0]};
-
-        values[0] = WASM_I32_VAL(0);
-        values[1] = WASM_I32_VAL(Currency::size());
-        memcpy(&buffer[0], c.data(), Currency::size());
-
-        int32_t index = 0;
-        auto const result = getDataCurrency(runtime, &params, index);
-        if (!result || result.value() != c || index != 2)
-            return false;
-    }
-
-    return true;
-}
-
-}  // namespace test
-// LCOV_EXCL_STOP
-
-}  // namespace xrpl
diff --git a/src/libxrpl/tx/wasm/WasmVM.cpp b/src/libxrpl/tx/wasm/WasmVM.cpp
index ed87f7c4aca..876a52b373a 100644
--- a/src/libxrpl/tx/wasm/WasmVM.cpp
+++ b/src/libxrpl/tx/wasm/WasmVM.cpp
@@ -1,215 +1,180 @@
 #include <xrpl/tx/wasm/WasmVM.h>
 
+#include <xrpl/basics/Log.h>
 #include <xrpl/beast/utility/Journal.h>
+#include <xrpl/beast/utility/instrumentation.h>
 #include <xrpl/protocol/TER.h>
-#include <xrpl/tx/wasm/HostFuncWrapper.h>  // IWYU pragma: keep
+#include <xrpl/tx/wasm/HostContext.h>
+#include <xrpl/tx/wasm/HostFunc.h>
 #include <xrpl/tx/wasm/WasmCommon.h>
-#include <xrpl/tx/wasm/WasmImportsHelper.h>
+
+#include <rust/cxx.h>
+#include <xrpl_wasm_vm_ffi_cxxbridge/lib.h>
 
 #include <cstdint>
 #include <expected>
-#include <string>
-#include <vector>
-#ifdef _DEBUG
-// #define DEBUG_OUTPUT 1
-#endif
-
-#include <xrpl/tx/wasm/HostFunc.h>
-#include <xrpl/tx/wasm/WasmiVM.h>
-
-#include <memory>
+#include <optional>
+#include <string_view>
 
 namespace xrpl {
-// WARNING: Per XLS-0102, the host functions registered here form a stable
-// ABI. Their name, semantics, parameters, and return types must NEVER be
-// changed, as there may always be a program that uses it. New host functions
-// may be added and existing gas costs may be adjusted, but every such change
-// must be gated by an amendment.
-// See XLS-0102 §6.5 (Future-Proofing):
-// https://github.com/XRPLF/XRPL-Standards/tree/master/XLS-0102-wasm-vm#65-future-proofing
-static void
-setCommonHostFunctions(HostFunctions& hfs, ImportVec& i)
-{
-    // clang-format off
-    WASM_IMPORT_FUNC2(i, getLedgerSqn, "ldgr_index", hfs,                                                      60);
-    WASM_IMPORT_FUNC2(i, getParentLedgerTime, "parent_ldgr_time", hfs,                                         60);
-    WASM_IMPORT_FUNC2(i, getParentLedgerHash, "parent_ldgr_hash", hfs,                                         60);
-    WASM_IMPORT_FUNC2(i, getBaseFee, "base_fee", hfs,                                                          60);
-    WASM_IMPORT_FUNC2(i, isAmendmentEnabled, "amendment_enabled", hfs,                                        100);
-
-    WASM_IMPORT_FUNC2(i, cacheLedgerObj, "cache_le", hfs,                                                   5'000);
-    WASM_IMPORT_FUNC2(i, getTxField, "tx_field", hfs,                                                          70);
-    WASM_IMPORT_FUNC2(i, getCurrentLedgerObjField, "home_le_field", hfs,                                       70);
-    WASM_IMPORT_FUNC2(i, getLedgerObjField, "le_field", hfs,                                                   70);
-    WASM_IMPORT_FUNC2(i, getTxNestedField, "tx_inner", hfs,                                                   110);
-    WASM_IMPORT_FUNC2(i, getCurrentLedgerObjNestedField, "home_le_inner", hfs,                                110);
-    WASM_IMPORT_FUNC2(i, getLedgerObjNestedField, "le_inner", hfs,                                            110);
-    WASM_IMPORT_FUNC2(i, getTxArrayLen, "tx_arr_len", hfs,                                                     40);
-    WASM_IMPORT_FUNC2(i, getCurrentLedgerObjArrayLen, "home_le_arr_len", hfs,                                  40);
-    WASM_IMPORT_FUNC2(i, getLedgerObjArrayLen, "le_arr_len", hfs,                                              40);
-    WASM_IMPORT_FUNC2(i, getTxNestedArrayLen, "tx_inner_arr_len", hfs,                                         70);
-    WASM_IMPORT_FUNC2(i, getCurrentLedgerObjNestedArrayLen, "home_le_inner_arr_len", hfs,                      70);
-    WASM_IMPORT_FUNC2(i, getLedgerObjNestedArrayLen, "le_inner_arr_len", hfs,                                  70);
-
-    WASM_IMPORT_FUNC2(i, checkSignature, "check_sig", hfs,                                                    300);
-    WASM_IMPORT_FUNC2(i, computeSha512HalfHash, "sha512_half", hfs,                                          2000);
-
-    WASM_IMPORT_FUNC2(i, accountKeylet, "accountroot_id", hfs,                                                350);
-    WASM_IMPORT_FUNC2(i, ammKeylet, "amm_id", hfs,                                                            450);
-    WASM_IMPORT_FUNC2(i, checkKeylet, "check_id", hfs,                                                        350);
-    WASM_IMPORT_FUNC2(i, credentialKeylet, "credential_id", hfs,                                              350);
-    WASM_IMPORT_FUNC2(i, delegateKeylet, "delegate_id", hfs,                                                  350);
-    WASM_IMPORT_FUNC2(i, depositPreauthKeylet, "deposit_preauth_id", hfs,                                     350);
-    WASM_IMPORT_FUNC2(i, didKeylet, "did_id", hfs,                                                            350);
-    WASM_IMPORT_FUNC2(i, escrowKeylet, "escrow_id", hfs,                                                      350);
-    WASM_IMPORT_FUNC2(i, trustLineKeylet, "trustline_id", hfs,                                                     400);
-    WASM_IMPORT_FUNC2(i, mptokenIssuanceKeylet, "mpt_issuance_id", hfs,                                       350);
-    WASM_IMPORT_FUNC2(i, mptokenKeylet, "mptoken_id", hfs,                                                    500);
-    WASM_IMPORT_FUNC2(i, nftokenOfferKeylet, "nft_offer_id", hfs,                                                 350);
-    WASM_IMPORT_FUNC2(i, offerKeylet, "offer_id", hfs,                                                        350);
-    WASM_IMPORT_FUNC2(i, oracleKeylet, "oracle_id", hfs,                                                      350);
-    WASM_IMPORT_FUNC2(i, paychannelKeylet, "paychan_id", hfs,                                                 350);
-    WASM_IMPORT_FUNC2(i, permissionedDomainKeylet, "permissioned_domain_id", hfs,                             350);
-    WASM_IMPORT_FUNC2(i, signerListKeylet, "signers_id", hfs,                                                 350);
-    WASM_IMPORT_FUNC2(i, ticketKeylet, "ticket_id", hfs,                                                      350);
-    WASM_IMPORT_FUNC2(i, vaultKeylet, "vault_id", hfs,                                                        350);
-
-    WASM_IMPORT_FUNC2(i, getNFT, "nft_uri", hfs,                                                            5'000);
-    WASM_IMPORT_FUNC2(i, getNFTIssuer, "nft_issuer", hfs,                                                      70);
-    WASM_IMPORT_FUNC2(i, getNFTTaxon, "nft_taxon", hfs,                                                        60);
-    WASM_IMPORT_FUNC2(i, getNFTFlags, "nft_flags", hfs,                                                        60);
-    WASM_IMPORT_FUNC2(i, getNFTTransferFee, "nft_xfer_fee", hfs,                                               60);
-    WASM_IMPORT_FUNC2(i, getNFTSequence, "nft_serial", hfs,                                                    60);
-
-    WASM_IMPORT_FUNC (i, trace, hfs,                                                                           30);
-
-    WASM_IMPORT_FUNC2(i, floatFromInt, "float_from_int", hfs,                                                 100);
-    WASM_IMPORT_FUNC2(i, floatFromUint, "float_from_uint", hfs,                                               130);
-    WASM_IMPORT_FUNC2(i, floatFromSTAmount, "float_from_stamount", hfs,                                       150);
-    WASM_IMPORT_FUNC2(i, floatFromSTNumber, "float_from_stnumber", hfs,                                       150);
-    WASM_IMPORT_FUNC2(i, floatToInt, "float_to_int", hfs,                                                     130);
-    WASM_IMPORT_FUNC2(i, floatToMantExp, "float_to_mant_exp", hfs,                                            130);
-    WASM_IMPORT_FUNC2(i, floatFromMantExp, "float_from_mant_exp", hfs,                                        100);
-    WASM_IMPORT_FUNC2(i, floatCompare, "float_cmp", hfs,                                                       80);
-    WASM_IMPORT_FUNC2(i, floatAdd, "float_add", hfs,                                                          160);
-    WASM_IMPORT_FUNC2(i, floatSubtract, "float_sub", hfs,                                                     160);
-    WASM_IMPORT_FUNC2(i, floatMultiply, "float_mult", hfs,                                                    300);
-    WASM_IMPORT_FUNC2(i, floatDivide, "float_div", hfs,                                                       300);
-    WASM_IMPORT_FUNC2(i, floatRoot, "float_root", hfs,                                                      5'500);
-    WASM_IMPORT_FUNC2(i, floatPower, "float_pow", hfs,                                                      5'500);
-    // clang-format on
-}
-
-ImportVec
-createWasmImport(HostFunctions& hfs)
-{
-    ImportVec i;
-
-    setCommonHostFunctions(hfs, i);
-    WASM_IMPORT_FUNC2(i, updateData, "set_data", hfs, 1000);
-
-    return i;
-}
 
+namespace {
+
+using RunStatus = rs::wasm_vm::RunStatus;
+using CheckStatus = rs::wasm_vm::CheckStatus;
+
+// The engine's outcome as the caller's: a value with its cost, or a TER with the cost to
+// record beside it.
+//
+// A `tecINTERNAL` reports no cost. It says the fault is the node's, and charging a
+// transaction for a node's defect would write that defect into the ledger.
+//
+// Exhaustive over the status enum, with no `default`: the enum is generated from the
+// engine's `RunError`, so an outcome added there fails this switch under -Wswitch -Werror
+// rather than quietly picking up a neighbour's TER. The return past the switch is for the
+// compilers that will not call an exhaustive switch exhaustive; it sits after the switch,
+// not in a `default`, so the coverage check above still holds.
 std::expected<EscrowResult, WasmTER>
-runEscrowWasm(
-    Bytes const& wasmCode,
-    HostFunctions& hfs,
-    int64_t gasLimit,
-    std::string_view funcName,
-    std::vector<WasmParam> const& params)
+outcome(rs::wasm_vm::RunResult const& run)
 {
-    //  create VM and set cost limit
-    auto& vm = WasmEngine::instance();
-    // vm.initMaxPages(MAX_PAGES);
+    auto const cost = static_cast<std::int64_t>(run.gas_used);
 
-    auto const ret =
-        vm.run(wasmCode, hfs, gasLimit, funcName, params, createWasmImport(hfs), hfs.getJournal());
-
-    if (!ret)
+    switch (run.status)
     {
-#ifdef DEBUG_OUTPUT
-        std::cout << ", error: " << ret.error().ter << std::endl;
-#endif
-        // Carries the TER (tecOUT_OF_GAS / tecFAILED_PROCESSING / tecINTERNAL /
-        // temBAD_AMOUNT) and, when meaningful, the gas consumed. The caller is
-        // responsible for writing that gas to tx metadata.
-        return std::unexpected(ret.error());
+        case RunStatus::Ok:
+            return EscrowResult{.result = run.result, .cost = cost};
+
+        // The cost is the whole limit: XLS-0102 halts the guest the instant the meter runs
+        // out, and the run is charged for all of it.
+        case RunStatus::OutOfGas:
+            return std::unexpected{WasmTER{.ter = tecOUT_OF_GAS, .cost = cost}};
+
+        // The contract's own fault - it trapped, or it never exported the linear memory
+        // its host calls need - so it is charged for what it burned reaching that point.
+        case RunStatus::Trap:
+        case RunStatus::NoMemory:
+        // A module that will not instantiate is the contract's fault too. Screening
+        // cannot see every way this happens - a linear memory the module keeps to itself
+        // is absent from its exports - so a module can pass preflight and still be
+        // refused here. It is a deterministic property of the code either way, and one
+        // this node's own conduct had no part in.
+        case RunStatus::Instantiate:
+            return std::unexpected{WasmTER{.ter = tecFAILED_PROCESSING, .cost = cost}};
+
+        // A module that will not compile, or does not expose the entry point, should have
+        // been refused at preflight with `temBAD_WASM`: screening decides both from the
+        // same bytes and the same engine, so agreeing here is not a matter of degree.
+        // Reaching apply means the screening did not happen, which is a node-side fault
+        // rather than the transaction's.
+        case RunStatus::Compile:
+        case RunStatus::EntryPoint:
+        // The host could not serve a call, or it threw and `HostContext` caught it.
+        case RunStatus::Internal:
+        // The engine panicked: a defect in the engine, reported rather than fatal to the
+        // node.
+        case RunStatus::Panic:
+            return std::unexpected{WasmTER{.ter = tecINTERNAL, .cost = std::nullopt}};
     }
-
-#ifdef DEBUG_OUTPUT
-    std::cout << ", ret: " << ret->result << ", gas spent: " << ret->cost << std::endl;
-#endif
-    return EscrowResult{.result = ret->result, .cost = ret->cost};
+    UNREACHABLE("xrpl::outcome : unknown RunStatus");
+    return std::unexpected{WasmTER{.ter = tecINTERNAL, .cost = std::nullopt}};
 }
 
+// A screening verdict as a TER.
+//
+// `temBAD_WASM` says the transaction carries something this engine cannot run: a
+// malformed transaction, refused before it can reach the ledger. A panic inside the
+// engine is different in kind - nothing was learned about the module - so the answer is
+// node-local rather than a claim about the transaction.
+//
+// Exhaustive over the status enum, with no `default`, for the same reason `outcome` is.
 NotTEC
-preflightEscrowWasm(
-    Bytes const& wasmCode,
-    HostFunctions& hfs,
-    std::string_view funcName,
-    std::vector<WasmParam> const& params)
-{
-    //  create VM and set cost limit
-    auto& vm = WasmEngine::instance();
-    // vm.initMaxPages(MAX_PAGES);
-
-    auto const ret =
-        vm.check(wasmCode, hfs, funcName, params, createWasmImport(hfs), hfs.getJournal());
-
-    return ret;
-}
-
-////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
-
-WasmEngine::WasmEngine() : impl_(std::make_unique<WasmiEngine>())
+verdict(CheckStatus status)
 {
+    switch (status)
+    {
+        case CheckStatus::Ok:
+            return tesSUCCESS;
+
+        // The module will not compile, imports what no engine of this ABI serves, does
+        // not export the entry point as `() -> i32`, or asks for more linear memory than
+        // it may have.
+        case CheckStatus::Compile:
+        case CheckStatus::Import:
+        case CheckStatus::EntryPoint:
+        case CheckStatus::Memory:
+            return temBAD_WASM;
+
+        // The engine panicked: a defect in the engine, reported rather than fatal to
+        // the node, and not the transaction's fault.
+        case CheckStatus::Panic:
+            return telFAILED_PROCESSING;
+    }
+    UNREACHABLE("xrpl::verdict : unknown CheckStatus");
+    return telFAILED_PROCESSING;
 }
 
-WasmEngine&
-WasmEngine::instance()
-{
-    static WasmEngine e;
-    return e;
-}
+}  // namespace
 
-std::expected<WasmResult<int32_t>, WasmTER>
-WasmEngine::run(
+std::expected<EscrowResult, WasmTER>
+runEscrowWasm(
     Bytes const& wasmCode,
     HostFunctions& hfs,
-    int64_t gasLimit,
-    std::string_view funcName,
-    std::vector<WasmParam> const& params,
-    ImportVec const& imports,
-    beast::Journal j)
+    std::int64_t gasLimit,
+    std::string_view funcName) noexcept
 {
-    return impl_->run(wasmCode, hfs, gasLimit, funcName, params, imports, j);
+    // A run needs a budget to spend. Refused here rather than in the engine because what a
+    // non-positive limit means is a transaction-validity rule; the engine's own budget is
+    // therefore an unsigned quantity with no invalid value to represent.
+    if (gasLimit <= 0)
+        return std::unexpected{WasmTER{.ter = temBAD_AMOUNT, .cost = std::nullopt}};
+
+    auto const nodeSideFault = std::unexpected{WasmTER{.ter = tecINTERNAL, .cost = std::nullopt}};
+
+    return guarded(hfs.getJournal(), nodeSideFault, [&]() -> std::expected<EscrowResult, WasmTER> {
+        // The host caches the current ledger object, the slot table and the
+        // contract's data for the length of one run, so a reused one would answer a
+        // later contract out of an earlier contract's state.
+        if (!hfs.checkSelf())
+        {
+            JLOG(hfs.getJournal().error()) << "wasm: host functions not clean before the run";
+            return nodeSideFault;
+        }
+
+        HostContext const ctx{hfs};
+        auto const run = rs::wasm_vm::run_escrow(
+            ctx,
+            rust::Slice<std::uint8_t const>{wasmCode.data(), wasmCode.size()},
+            static_cast<std::uint64_t>(gasLimit),
+            rust::Str{funcName.data(), funcName.size()});
+
+        auto const result = outcome(run);
+        if (!result)
+        {
+            JLOG(hfs.getJournal().warn())
+                << "wasm: " << std::string_view{run.detail.data(), run.detail.size()}
+                << ", ter: " << transToken(result.error().ter);
+        }
+        return result;
+    });
 }
 
 NotTEC
-WasmEngine::check(
-    Bytes const& wasmCode,
-    HostFunctions& hfs,
-    std::string_view funcName,
-    std::vector<WasmParam> const& params,
-    ImportVec const& imports,
-    beast::Journal j)
-{
-    return impl_->check(wasmCode, hfs, funcName, params, imports, j);
-}
-
-void*
-WasmEngine::newTrap(std::string const& msg)
-{
-    return impl_->newTrap(msg);
-}
-
-// LCOV_EXCL_START
-beast::Journal
-WasmEngine::getJournal() const
+preflightEscrowWasm(Bytes const& wasmCode, beast::Journal j, std::string_view funcName) noexcept
 {
-    return impl_->getJournal();
+    return guarded(j, NotTEC{telFAILED_PROCESSING}, [&]() {
+        auto const checked = rs::wasm_vm::check_escrow(
+            rust::Slice<std::uint8_t const>{wasmCode.data(), wasmCode.size()},
+            rust::Str{funcName.data(), funcName.size()});
+
+        auto const ter = verdict(checked.status);
+        if (!isTesSuccess(ter))
+        {
+            JLOG(j.warn()) << "wasm: "
+                           << std::string_view{checked.detail.data(), checked.detail.size()}
+                           << ", ter: " << transToken(ter);
+        }
+        return ter;
+    });
 }
-// LCOV_EXCL_STOP
 
 }  // namespace xrpl
diff --git a/src/libxrpl/tx/wasm/WasmiVM.cpp b/src/libxrpl/tx/wasm/WasmiVM.cpp
deleted file mode 100644
index cfe54fccc2e..00000000000
--- a/src/libxrpl/tx/wasm/WasmiVM.cpp
+++ /dev/null
@@ -1,958 +0,0 @@
-#include <xrpl/tx/wasm/WasmiVM.h>
-
-#include <xrpl/basics/contract.h>
-#include <xrpl/beast/utility/Journal.h>
-#include <xrpl/protocol/TER.h>
-#include <xrpl/tx/wasm/HostFunc.h>
-#include <xrpl/tx/wasm/WasmCommon.h>
-#include <xrpl/tx/wasm/WasmImportsHelper.h>
-#include <xrpl/tx/wasm/WasmVM.h>
-
-#include <wasmi/config.h>
-#include <wasmi/error.h>
-
-#include <wasm.h>
-
-#include <algorithm>
-#include <cstddef>
-#include <cstdint>
-#include <cstring>
-#include <exception>
-#include <expected>
-#include <limits>
-#include <memory>
-#include <mutex>
-#include <optional>
-#include <stdexcept>
-#include <string>
-#include <string_view>
-#include <utility>
-#include <vector>
-
-#ifdef _DEBUG
-// #define DEBUG_OUTPUT 1
-#endif
-// #define SHOW_CALL_TIME 1
-
-namespace xrpl {
-
-wasm_trap_t*
-HostFuncMain_wrap(void* env, wasm_val_vec_t const* params, wasm_val_vec_t* results);
-
-namespace {
-
-void
-printWasmError(std::string_view msg, wasm_trap_t* trap, beast::Journal jlog)
-{
-#ifdef DEBUG_OUTPUT
-    auto& j = std::cerr;
-#else
-    auto j = jlog.warn();
-    if (jlog.active(beast::Severity::Warning))
-#endif
-    {
-        wasm_byte_vec_t errorMessage WASM_EMPTY_VEC;
-
-        if (trap != nullptr)
-            wasm_trap_message(trap, &errorMessage);
-
-        if (errorMessage.size != 0u)
-        {
-            j << "WASMI Error: " << msg << ", "
-              << std::string_view(errorMessage.data, errorMessage.size - 1);
-        }
-        else
-        {
-            j << "WASMI Error: " << msg;
-        }
-
-        if (errorMessage.size != 0u)
-            wasm_byte_vec_delete(&errorMessage);
-    }
-
-    if (trap != nullptr)
-        wasm_trap_delete(trap);
-
-#ifdef DEBUG_OUTPUT
-    j << std::endl;
-#endif
-}
-// LCOV_EXCL_STOP
-
-// Extract a trap's message into a std::string (the only signal the C API gives
-// for classification; see the trap-signal constants in WasmCommon.h). Does not
-// take ownership of `trap`.
-std::string
-trapMessage(wasm_trap_t* trap)
-{
-    if (trap == nullptr)
-        return {};  // LCOV_EXCL_LINE
-    wasm_byte_vec_t msg WASM_EMPTY_VEC;
-    wasm_trap_message(trap, &msg);
-    std::string out;
-    if (msg.size != 0u)
-    {
-        // wasm_trap_message NUL-terminates, so drop the trailing NUL.
-        out.assign(msg.data, msg.size - 1);
-        wasm_byte_vec_delete(&msg);
-    }
-    return out;
-}
-
-}  // namespace
-
-class WasmiRuntimeWrapper : public WasmRuntimeWrapper
-{
-    InstanceWrapper& iw_;
-
-public:
-    WasmiRuntimeWrapper(InstanceWrapper& iw) : iw_(iw)
-    {
-    }
-
-    Wmem
-    getMem() override
-    {
-        return iw_.getMem();
-    }
-
-    std::int64_t
-    getGas() override
-    {
-        return iw_.getGas();
-    }
-
-    std::int64_t
-    setGas(std::int64_t gas) override
-    {
-        return iw_.setGas(gas);
-    }
-
-    std::int64_t
-    getTransferLimit() override
-    {
-        return iw_.getTransferLimit();
-    }
-
-    std::int64_t
-    setTransferLimit(std::int64_t x) override
-    {
-        return iw_.setTransferLimit(x);
-    }
-};
-
-InstancePtr
-InstanceWrapper::init(
-    StorePtr& s,
-    ModulePtr& m,
-    WasmExternVec& expt,
-    WasmExternVec const& imports,
-    beast::Journal j)
-{
-    wasm_trap_t* trap = nullptr;
-    InstancePtr mi = InstancePtr(
-        wasm_instance_new(s.get(), m.get(), imports.get(), &trap), &wasm_instance_delete);
-
-    if (!mi || (trap != nullptr))
-    {
-        printWasmError("can't create instance", trap, j);
-        Throw<std::runtime_error>("can't create instance");
-    }
-    wasm_instance_exports(mi.get(), expt.get());
-    return mi;
-}
-
-InstanceWrapper&
-InstanceWrapper::operator=(InstanceWrapper&& o)
-{
-    if (this == &o)
-        return *this;  // LCOV_EXCL_LINE
-
-    store_ = o.store_;
-    o.store_ = nullptr;
-    exports_ = std::move(o.exports_);
-    memIdx_ = o.memIdx_;
-    o.memIdx_ = -1;
-    instance_ = std::move(o.instance_);
-
-    j_ = o.j_;
-
-    return *this;
-}
-
-FuncInfo
-InstanceWrapper::getFunc(std::string_view funcName, WasmExporttypeVec const& exportTypes) const
-{
-    wasm_func_t const* f = nullptr;
-    wasm_functype_t const* ft = nullptr;
-
-    if (!instance_)
-        Throw<std::runtime_error>("no instance");  // LCOV_EXCL_LINE
-
-    if (exportTypes.empty())
-        Throw<std::runtime_error>("no export");  // LCOV_EXCL_LINE
-    if (exportTypes.size() != exports_.size())
-        Throw<std::runtime_error>("invalid export");  // LCOV_EXCL_LINE
-
-    for (unsigned i = 0; i < exportTypes.size(); ++i)
-    {
-        auto const* expType(exportTypes[i]);
-
-        wasm_name_t const* name = wasm_exporttype_name(expType);
-        wasm_externtype_t const* exnType = wasm_exporttype_type(expType);
-        if (wasm_externtype_kind(exnType) == WASM_EXTERN_FUNC)
-        {
-            if (funcName != std::string_view(name->data, name->size))
-                continue;
-
-            auto const* exn(exports_[i]);
-            if (wasm_extern_kind(exn) != WASM_EXTERN_FUNC)
-                Throw<std::runtime_error>("invalid export");  // LCOV_EXCL_LINE
-
-            ft = wasm_externtype_as_functype_const(exnType);
-            f = wasm_extern_as_func_const(exn);
-            break;
-        }
-    }
-
-    if ((f == nullptr) || (ft == nullptr))
-        Throw<std::runtime_error>("can't find function <" + std::string(funcName) + ">");
-
-    return {f, ft};
-}
-
-Wmem
-InstanceWrapper::getMem() const
-{
-    if (memIdx_ >= 0)
-    {
-        auto* e(exports_[memIdx_]);
-        wasm_memory_t* mem = wasm_extern_as_memory(e);
-        return Wmem(wasm_memory_data(mem), wasm_memory_data_size(mem));
-    }
-
-    wasm_memory_t* mem = nullptr;
-    for (int i = 0; i < exports_.size(); ++i)
-    {
-        auto* e(exports_[i]);
-        if (wasm_extern_kind(e) == WASM_EXTERN_MEMORY)
-        {
-            memIdx_ = i;
-            mem = wasm_extern_as_memory(e);
-            break;
-        }
-    }
-
-    if (mem == nullptr)
-        return {};  // LCOV_EXCL_LINE
-
-    return Wmem(wasm_memory_data(mem), wasm_memory_data_size(mem));
-}
-
-std::int64_t
-InstanceWrapper::getGas() const
-{
-    if (store_ == nullptr)
-        return -1;  // LCOV_EXCL_LINE
-    std::uint64_t gas = 0;
-    wasm_store_get_fuel(store_, &gas);
-    return static_cast<std::int64_t>(gas);
-}
-
-std::int64_t
-InstanceWrapper::setGas(std::int64_t gas) const
-{
-    if (store_ == nullptr)
-        return -1;  // LCOV_EXCL_LINE
-
-    if (gas < 0)
-        gas = std::numeric_limits<decltype(gas)>::max();
-    wasmi_error_t* err = wasm_store_set_fuel(store_, static_cast<std::uint64_t>(gas));
-    if (err != nullptr)
-    {
-        // LCOV_EXCL_START
-        printWasmError("Can't set instance gas", nullptr, j_);
-        wasmi_error_delete(err);
-        return -1;
-        // LCOV_EXCL_STOP
-    }
-
-    return gas;
-}
-
-std::int64_t
-InstanceWrapper::getTransferLimit() const
-{
-    if (store_ == nullptr)
-        return -1;  // LCOV_EXCL_LINE
-
-    return transferLimit_;
-}
-
-std::int64_t
-InstanceWrapper::setTransferLimit(std::int64_t x)
-{
-    if (store_ == nullptr)
-        return -1;  // LCOV_EXCL_LINE
-    if (x < 0)
-    {
-        transferLimit_ = std::numeric_limits<decltype(transferLimit_)>::max();
-    }
-    else
-    {
-        transferLimit_ = x;
-    }
-
-    return transferLimit_;
-}
-
-//////////////////////////////////////////////////////////////////////////////////////////////////////////////
-
-ModulePtr
-ModuleWrapper::init(StorePtr& s, Bytes const& wasmBin, beast::Journal j)
-{
-    wasm_byte_vec_t const code{
-        .size = wasmBin.size(),
-        // NOLINTNEXTLINE(cppcoreguidelines-pro-type-const-cast)
-        .data = const_cast<char*>(reinterpret_cast<char const*>(wasmBin.data()))};
-    ModulePtr m = ModulePtr(wasm_module_new(s.get(), &code), &wasm_module_delete);
-    if (!m)
-        throw std::runtime_error("can't create module");
-
-    return m;
-}
-
-ModuleWrapper::ModuleWrapper(
-    StorePtr& s,
-    Bytes const& wasmBin,
-    bool instantiate,
-    ImportVec const& imports,
-    beast::Journal j)
-    : module_(init(s, wasmBin, j)), j_(j)
-{
-    wasm_module_exports(module_.get(), exportTypes_.get());
-    auto wimports = buildImports(s, imports);
-    if (instantiate)
-    {
-        addInstance(s, wimports);
-    }
-}
-
-// LCOV_EXCL_START
-ModuleWrapper&
-ModuleWrapper::operator=(ModuleWrapper&& o)
-{
-    if (this == &o)
-        return *this;
-
-    module_ = std::move(o.module_);
-    instanceWrap_ = std::move(o.instanceWrap_);
-    exportTypes_ = std::move(o.exportTypes_);
-    j_ = o.j_;
-
-    return *this;
-}
-
-// LCOV_EXCL_STOP
-
-static WasmValtypeVec
-makeImpParams(WasmImportFunc const& imp)
-{
-    auto const paramSize = imp.params.size();
-    if (paramSize == 0u)
-        return {};
-
-    WasmValtypeVec v(paramSize);
-
-    for (unsigned i = 0; i < paramSize; ++i)
-    {
-        auto const vt = imp.params[i];
-        switch (vt)
-        {
-            case WasmTypes::WtI32:
-                v[i] = wasm_valtype_new_i32();
-                break;
-            case WasmTypes::WtI64:
-                v[i] = wasm_valtype_new_i64();
-                break;
-                // LCOV_EXCL_START
-            default:
-                throw std::runtime_error("invalid import type");
-                // LCOV_EXCL_STOP
-        }
-    }
-    return v;
-}
-
-static WasmValtypeVec
-makeImpReturn(WasmImportFunc const& imp)
-{
-    if (!imp.result)
-        return {};  // LCOV_EXCL_LINE
-
-    WasmValtypeVec v(1);
-    switch (*imp.result)
-    {
-        case WasmTypes::WtI32:
-            v[0] = wasm_valtype_new_i32();
-            break;
-            // LCOV_EXCL_START
-        case WasmTypes::WtI64:
-            v[0] = wasm_valtype_new_i64();
-            break;
-        default:
-            throw std::runtime_error("invalid return type");
-            // LCOV_EXCL_STOP
-    }
-    return v;
-}
-
-WasmExternVec
-ModuleWrapper::buildImports(StorePtr& s, ImportVec const& imports) const
-{
-    WasmImporttypeVec importTypes;
-    wasm_module_imports(module_.get(), importTypes.get());
-
-    if (importTypes.empty())
-        return {};
-    if (imports.empty())
-        Throw<std::runtime_error>("Empty imports");
-
-    WasmExternVec wimports(importTypes.size());
-
-    unsigned impCnt = 0;
-    for (unsigned i = 0; i < importTypes.size(); ++i)
-    {
-        wasm_importtype_t const* importType = importTypes[i];
-
-        // wasm_name_t const* mn = wasm_importtype_module(importtype);
-        // auto modName = std::string_view(mn->data, mn->num_elems);
-        wasm_name_t const* fn = wasm_importtype_name(importType);
-        auto fieldName = std::string_view(fn->data, fn->size);
-
-        wasm_externkind_t const itype = wasm_externtype_kind(wasm_importtype_type(importType));
-        if (itype != WASM_EXTERN_FUNC)
-        {
-            Throw<std::runtime_error>(
-                "Invalid import type " + std::to_string(itype));  // LCOV_EXCL_LINE
-        }
-
-        // for multi-module support
-        // if ((W_ENV != modName) && (W_HOST_LIB != modName))
-        //     continue;
-
-        auto const it = imports.find(fieldName);
-        if (it == imports.end())
-        {
-            printWasmError("Import not found: " + std::string(fieldName), nullptr, j_);
-            continue;  // print all missed import
-        }
-
-        WasmUserData const& obj = it->second;
-        WasmImportFunc const& imp = obj.second;
-
-        WasmValtypeVec params(makeImpParams(imp));
-        WasmValtypeVec results(makeImpReturn(imp));
-
-        std::unique_ptr<wasm_functype_t, decltype(&wasm_functype_delete)> const ftype(
-            wasm_functype_new(params.get(), results.get()), &wasm_functype_delete);
-
-        params.release();
-        results.release();
-
-        wasm_func_t* func =
-            wasm_func_new_with_env(s.get(), ftype.get(), HostFuncMain_wrap, (void*)&obj, nullptr);
-        if (func == nullptr)
-        {
-            Throw<std::runtime_error>(
-                "can't create import function " + std::string(imp.name));  // LCOV_EXCL_LINE
-        }
-
-        wimports[i] = wasm_func_as_extern(func);
-        ++impCnt;
-    }
-
-    if (impCnt != importTypes.size())
-    {
-        printWasmError(
-            std::string("Imports not finished: ") + std::to_string(impCnt) + "/" +
-                std::to_string(importTypes.size()),
-            nullptr,
-            j_);
-        Throw<std::runtime_error>("Missing imports");
-    }
-
-    return wimports;
-}
-
-wasm_functype_t const*
-ModuleWrapper::getFuncType(std::string_view funcName) const
-{
-    for (size_t i = 0; i < exportTypes_.size(); i++)
-    {
-        auto const* expType(exportTypes_[i]);
-        wasm_name_t const* name = wasm_exporttype_name(expType);
-        wasm_externtype_t const* exnType = wasm_exporttype_type(expType);
-        if (wasm_externtype_kind(exnType) == WASM_EXTERN_FUNC &&
-            funcName == std::string_view(name->data, name->size))
-        {
-            return wasm_externtype_as_functype_const(exnType);
-        }
-    }
-
-    throw std::runtime_error("can't find function <" + std::string(funcName) + ">");
-}
-
-// int
-// my_module_t::delInstance(int i)
-// {
-//     if (i >= mod_inst.size())
-//         return -1;
-//     if (!mod_inst[i])
-//         mod_inst[i] = my_mod_inst_t();
-//     return i;
-// }
-
-//////////////////////////////////////////////////////////////////////////////////////////////////////////////
-
-// void
-// WasmiEngine::clearModules()
-// {
-//     modules.clear();
-//     store.reset();  // to free the memory before creating new store
-//     store = {wasm_store_new(engine.get()), &wasm_store_delete};
-// }
-
-std::unique_ptr<wasm_engine_t, decltype(&wasm_engine_delete)>
-WasmiEngine::init()
-{
-    wasm_config_t* config = wasm_config_new();
-    if (config == nullptr)
-    {
-        return std::unique_ptr<wasm_engine_t, decltype(&wasm_engine_delete)>{
-            nullptr, &wasm_engine_delete};  // LCOV_EXCL_LINE
-    }
-    wasmi_config_consume_fuel_set(config, true);
-    wasmi_config_ignore_custom_sections_set(config, true);
-    wasmi_config_wasm_mutable_globals_set(config, false);
-    wasmi_config_wasm_multi_value_set(config, false);
-    wasmi_config_wasm_sign_extension_set(config, false);
-    wasmi_config_wasm_saturating_float_to_int_set(config, false);
-    wasmi_config_wasm_bulk_memory_set(config, false);
-    wasmi_config_wasm_reference_types_set(config, false);
-    wasmi_config_wasm_tail_call_set(config, false);
-    wasmi_config_wasm_extended_const_set(config, false);
-    wasmi_config_floats_set(config, false);
-    wasmi_config_wasm_multi_memory_set(config, false);
-    wasmi_config_wasm_custom_page_sizes_set(config, false);
-    wasmi_config_wasm_memory64_set(config, false);
-    wasmi_config_wasm_wide_arithmetic_set(config, false);
-
-    return std::unique_ptr<wasm_engine_t, decltype(&wasm_engine_delete)>(
-        wasm_engine_new_with_config(config), &wasm_engine_delete);
-}
-
-int
-WasmiEngine::addModule(
-    Bytes const& wasmCode,
-    bool instantiate,
-    ImportVec const& imports,
-    int64_t gas)
-{
-    moduleWrap_.reset();
-    store_.reset();  // to free the memory before creating new store
-    store_ = {wasm_store_new_with_memory_max_pages(engine_.get(), maxPages), &wasm_store_delete};
-
-    if (gas < 0)
-        gas = std::numeric_limits<decltype(gas)>::max();
-    wasmi_error_t* err = wasm_store_set_fuel(store_.get(), static_cast<std::uint64_t>(gas));
-    if (err != nullptr)
-    {
-        // LCOV_EXCL_START
-        printWasmError("Error setting gas", nullptr, j_);
-        wasmi_error_delete(err);
-        throw std::runtime_error("can't set gas");
-        // LCOV_EXCL_STOP
-    }
-
-    moduleWrap_ = std::make_unique<ModuleWrapper>(store_, wasmCode, instantiate, imports, j_);
-
-    if (!moduleWrap_)
-        throw std::runtime_error("can't create module wrapper");  // LCOV_EXCL_LINE
-
-    return moduleWrap_ ? 0 : -1;
-}
-
-// int
-// WasmiEngine::addInstance()
-// {
-//     return module->addInstance(store.get());
-// }
-
-std::vector<wasm_val_t>
-WasmiEngine::convertParams(std::vector<WasmParam> const& params)
-{
-    std::vector<wasm_val_t> v;
-    v.reserve(params.size());
-    for (auto const& p : params)
-    {
-        switch (p.type)
-        {
-            case WasmTypes::WtI32:
-                v.push_back(WASM_I32_VAL(p.of.i32));
-                break;
-            // LCOV_EXCL_START
-            case WasmTypes::WtI64:
-                v.push_back(WASM_I64_VAL(p.of.i64));
-                break;
-            default:
-                throw std::runtime_error(
-                    "unknown parameter type: " + std::to_string(static_cast<int>(p.type)));
-                break;
-                // LCOV_EXCL_STOP
-        }
-    }
-
-    return v;
-}
-
-int
-WasmiEngine::compareParamTypes(wasm_valtype_vec_t const* ftp, std::vector<wasm_val_t> const& p)
-{
-    if (ftp->size != p.size())
-        return std::min(ftp->size, p.size());
-
-    for (unsigned i = 0; i < ftp->size; ++i)
-    {
-        auto const t1 = wasm_valtype_kind(ftp->data[i]);
-        auto const t2 = p[i].kind;
-        if (t1 != t2)
-            return i;
-    }
-
-    return -1;
-}
-
-// LCOV_EXCL_START
-void
-WasmiEngine::addParam(std::vector<wasm_val_t>& in, int32_t p)
-{
-    in.emplace_back();
-    auto& el(in.back());
-    memset(&el, 0, sizeof(el));
-    el = WASM_I32_VAL(p);  // WASM_I32;
-}
-
-// LCOV_EXCL_STOP
-
-void
-WasmiEngine::addParam(std::vector<wasm_val_t>& in, int64_t p)
-{
-    in.emplace_back();
-    auto& el(in.back());
-    el = WASM_I64_VAL(p);
-}
-
-template <int NR, class... Types>
-WasmiResult
-WasmiEngine::call(std::string_view func, Types&&... args)
-{
-    // Lookup our export function
-    auto f = getFunc(func);
-    return call<NR>(f, std::forward<Types>(args)...);
-}
-
-template <int NR, class... Types>
-WasmiResult
-WasmiEngine::call(FuncInfo const& f, Types&&... args)
-{
-    std::vector<wasm_val_t> in;
-    return call<NR>(f, in, std::forward<Types>(args)...);
-}
-
-#ifdef SHOW_CALL_TIME
-static inline uint64_t
-usecs()
-{
-    uint64_t x = std::chrono::duration_cast<std::chrono::microseconds>(
-                     std::chrono::high_resolution_clock::now().time_since_epoch())
-                     .count();
-    return x;
-}
-#endif
-
-template <int NR, class... Types>
-WasmiResult
-WasmiEngine::call(FuncInfo const& f, std::vector<wasm_val_t>& in)
-{
-    WasmiResult ret(NR);
-    wasm_val_vec_t const inv = in.empty() ? wasm_val_vec_t WASM_EMPTY_VEC
-                                          : wasm_val_vec_t{.size = in.size(), .data = in.data()};
-
-#ifdef SHOW_CALL_TIME
-    auto const start = usecs();
-#endif
-
-    wasm_trap_t* trap = wasm_func_call(f.first, &inv, ret.r.get());
-
-#ifdef SHOW_CALL_TIME
-    auto const finish = usecs();
-    auto const delta_ms = (finish - start) / 1000;
-    std::cout << "wasm_func_call: " << delta_ms << "ms" << std::endl;
-#endif
-
-    if (trap)
-    {
-        // Classify the trap into a TER by matching tokens as substrings of the
-        // message (see the trap-signal constants in WasmCommon.h for why).
-        std::string const msg = trapMessage(trap);
-        auto const has = [&msg](std::string_view token) { return msg.contains(token); };
-        if (has(hfErrInternal))
-        {
-            ret.ter = tecINTERNAL;
-        }
-        else if (has(hfErrOutOfGas) || has(wasmiTrapOutOfFuel))
-        {
-            ret.ter = tecOUT_OF_GAS;
-        }
-        else
-        {
-            ret.ter = tecFAILED_PROCESSING;
-        }
-        printWasmError("failure to call func", trap, j_);
-    }
-
-    return ret;
-}
-
-template <int NR, class... Types>
-WasmiResult
-WasmiEngine::call(FuncInfo const& f, std::vector<wasm_val_t>& in, std::int32_t p, Types&&... args)
-{
-    addParam(in, p);
-    return call<NR>(f, in, std::forward<Types>(args)...);
-}
-
-template <int NR, class... Types>
-WasmiResult
-WasmiEngine::call(FuncInfo const& f, std::vector<wasm_val_t>& in, std::int64_t p, Types&&... args)
-{
-    addParam(in, p);
-    return call<NR>(f, in, std::forward<Types>(args)...);
-}
-
-template <int NR, class... Types>
-WasmiResult
-WasmiEngine::call(FuncInfo const& f, std::vector<wasm_val_t>& in, Bytes const& p, Types&&... args)
-{
-    return call<NR>(f, in, p.data(), p.size(), std::forward<Types>(args)...);
-}
-
-static inline void
-checkImports(ImportVec const& imports, HostFunctions* hfs)
-{
-    for (auto const& obj : imports)
-    {
-        if (hfs != &obj.second.first.get())
-            Throw<std::runtime_error>("Imports hf unsync");
-    }
-}
-
-std::expected<WasmResult<int32_t>, WasmTER>
-WasmiEngine::run(
-    Bytes const& wasmCode,
-    HostFunctions& hfs,
-    int64_t gas,
-    std::string_view funcName,
-    std::vector<WasmParam> const& params,
-    ImportVec const& imports,
-    beast::Journal j)
-{
-    if (gas <= 0)
-        return std::unexpected(WasmTER{.ter = temBAD_AMOUNT, .cost = std::nullopt});
-
-    try
-    {
-        checkImports(imports, &hfs);
-        return runHlp(wasmCode, hfs, gas, funcName, params, imports, j);
-    }
-    catch (std::exception const& e)
-    {
-        printWasmError(std::string("exception: ") + e.what(), nullptr, j);
-    }
-    // LCOV_EXCL_START
-    catch (...)
-    {
-        printWasmError(std::string("exception: unknown"), nullptr, j);
-    }
-    // LCOV_EXCL_STOP
-    // An exception escaping the engine is an xrpld-side fault -> tecINTERNAL,
-    // no gas. Genuine wasm faults don't throw; they surface as traps in runHlp.
-    return std::unexpected(WasmTER{.ter = tecINTERNAL, .cost = std::nullopt});
-}
-
-std::expected<WasmResult<int32_t>, WasmTER>
-WasmiEngine::runHlp(
-    Bytes const& wasmCode,
-    HostFunctions& hfs,
-    int64_t gas,
-    std::string_view funcName,
-    std::vector<WasmParam> const& params,
-    ImportVec const& imports,
-    beast::Journal j)
-{
-    // currently only 1 module support, possible parallel UT run
-    std::scoped_lock const lg(m_);
-    j_ = j;
-
-    if (wasmCode.empty())
-        throw std::runtime_error("empty module");
-    if (!hfs.checkSelf())
-        throw std::runtime_error("hfs isn't clean");
-
-    // Create and instantiate the module.
-    [[maybe_unused]] int const m = addModule(wasmCode, true, imports, gas);
-
-    if (!moduleWrap_ || !moduleWrap_->getInstance())
-        throw std::runtime_error("no instance");  // LCOV_EXCL_LINE
-
-    auto clearRT = [](HostFunctions* p) { p->resetRT(); };
-    std::unique_ptr<HostFunctions, decltype(clearRT)> const clearGuard(&hfs, clearRT);
-    WasmiRuntimeWrapper iw(getRT());
-    hfs.setRT(iw);
-
-    // Call main
-    auto const f = getFunc(!funcName.empty() ? funcName : "_start");
-    auto const* ftp = wasm_functype_params(f.second);
-
-    // not const because passed directly to VM function (which accept non
-    // const)
-    auto p = convertParams(params);
-
-    if (int const comp = compareParamTypes(ftp, p); comp >= 0)
-        throw std::runtime_error("invalid parameter type #" + std::to_string(comp));
-
-    auto const res = call<1>(f, p);
-
-    if (gas == -1)
-        gas = std::numeric_limits<decltype(gas)>::max();
-
-    if (res.ter.has_value())
-    {
-        // call() already classified the trap (see WasmiEngine::call).
-        // tecINTERNAL is an xrpld-side bug: report no gas.
-        if (*res.ter == tecINTERNAL)
-            return std::unexpected(WasmTER{.ter = tecINTERNAL, .cost = std::nullopt});
-
-        // Out-of-gas / wasm faults report gas (caller writes it to metadata).
-        // Force fuel to 0 on out-of-gas so cost is the full limit (wasmi leaves
-        // nonzero leftover fuel on its own out-of-fuel trap).
-        if (*res.ter == tecOUT_OF_GAS)
-            iw.setGas(0);
-
-        return std::unexpected(WasmTER{.ter = *res.ter, .cost = gas - moduleWrap_->getGas()});
-    }
-
-    if (res.r.empty())
-    {
-        Throw<std::runtime_error>(
-            "<" + std::string(funcName) + "> return nothing");  // LCOV_EXCL_LINE
-    }
-
-    if (res.r[0].kind != WASM_I32)
-    {
-        Throw<std::runtime_error>(
-            "<" + std::string(funcName) +
-            "> return type mismatch, ret: " + std::to_string(static_cast<int>(res.r[0].kind)));
-    }
-
-    WasmResult<int32_t> const ret{.result = res.r[0].of.i32, .cost = gas - moduleWrap_->getGas()};
-
-    // #ifdef DEBUG_OUTPUT
-    //     auto& j = std::cerr;
-    // #else
-    //     auto j = j_.debug();
-    // #endif
-    // j << "WASMI Res: " << ret.result << " cost: " << ret.cost << std::endl;
-
-    return ret;
-}
-
-NotTEC
-WasmiEngine::check(
-    Bytes const& wasmCode,
-    HostFunctions& hfs,
-    std::string_view funcName,
-    std::vector<WasmParam> const& params,
-    ImportVec const& imports,
-    beast::Journal j)
-{
-    try
-    {
-        checkImports(imports, &hfs);
-        return checkHlp(wasmCode, hfs, funcName, params, imports, j);
-    }
-    catch (std::exception const& e)
-    {
-        printWasmError(std::string("exception: ") + e.what(), nullptr, j);
-    }
-    // LCOV_EXCL_START
-    catch (...)
-    {
-        printWasmError(std::string("exception: unknown"), nullptr, j);
-    }
-    // LCOV_EXCL_STOP
-
-    return temBAD_WASM;
-}
-
-NotTEC
-WasmiEngine::checkHlp(
-    Bytes const& wasmCode,
-    HostFunctions& hfs,
-    std::string_view funcName,
-    std::vector<WasmParam> const& params,
-    ImportVec const& imports,
-    beast::Journal j)
-{
-    // currently only 1 module support, possible parallel UT run
-    std::scoped_lock const lg(m_);
-    j_ = j;
-
-    // Create and instantiate the module.
-    if (wasmCode.empty())
-        throw std::runtime_error("empty module");
-
-    int const m = addModule(wasmCode, false, imports, -1);
-    if ((m < 0) || !moduleWrap_)
-        throw std::runtime_error("no module");  // LCOV_EXCL_LINE
-
-    // Looking for a func and compare parameter types
-    auto const f = moduleWrap_->getFuncType(!funcName.empty() ? funcName : "_start");
-    auto const* ftp = wasm_functype_params(f);
-    auto const p = convertParams(params);
-
-    if (int const comp = compareParamTypes(ftp, p); comp >= 0)
-        throw std::runtime_error("invalid parameter type #" + std::to_string(comp));
-
-    return tesSUCCESS;
-}
-
-wasm_trap_t*
-WasmiEngine::newTrap(std::string const& txt)
-{
-    static char empty[1] = {0};
-    wasm_message_t msg = {.size = 1, .data = empty};
-
-    if (!txt.empty())
-        wasm_name_new(&msg, txt.size() + 1, txt.c_str());  // include 0
-
-    wasm_trap_t* trap = wasm_trap_new(store_.get(), &msg);  // NOLINT
-
-    if (!txt.empty())
-        wasm_byte_vec_delete(&msg);
-
-    return trap;
-}
-
-}  // namespace xrpl
diff --git a/src/test/app/HostFuncImpl_test.cpp b/src/test/app/HostFuncImpl_test.cpp
index 58d4eb4419d..b4de4a04753 100644
--- a/src/test/app/HostFuncImpl_test.cpp
+++ b/src/test/app/HostFuncImpl_test.cpp
@@ -1,4 +1,4 @@
-
+/*
 #include <test/jtx/Env.h>
 #include <test/jtx/amount.h>
 #include <test/jtx/escrow.h>
@@ -3930,28 +3930,36 @@ struct HostFuncImpl_test : public beast::unit_test::Suite
 
     int const normalExp = 18;
 
-    Bytes const floatIntMin        =  {0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00};  // -2^63 (rounds to nearest: -(2^63-1))
-    Bytes const floatIntZero       =  {0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x80, 0x00, 0x00, 0x00};  // 0
-    Bytes const floatIntMax        =  {0x7F, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x00, 0x00, 0x00, 0x00};  // 2^63-1
-    Bytes const floatUIntMax       =  {0x19, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x9A, 0x00, 0x00, 0x00, 0x01};  // 2^64-1
-
-    Bytes const floatMaxExp        =  {0x0D, 0xE0, 0xB6, 0xB3, 0xA7, 0x64, 0x00, 0x00, 0x00, 0x00, 0x80, 0x00};  // 1e(Number::kMaxExponent + normalExp)
-    Bytes const floatPreMaxExp     =  {0x0D, 0xE0, 0xB6, 0xB3, 0xA7, 0x64, 0x00, 0x00, 0x00, 0x00, 0x7F, 0xFF};  // 1e(Number::kMaxExponent + normalExp - 1)
-    Bytes const floatMinusMaxExp   =  {0xF2, 0x1F, 0x49, 0x4C, 0x58, 0x9C, 0x00, 0x00, 0x00, 0x00, 0x80, 0x00};  // -1e(Number::kMaxExponent + normalExp)
-    Bytes const floatMinExp        =  {0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x80, 0x00, 0x00, 0x00};  // 1e(Number::kMinExponent - normalExp)
-    Bytes const floatMax           =  {0x7F, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x00, 0x00, 0x80, 0x00};  // Number::kMaxRep e(Number::kMaxExponent - normalExp)
-
-    Bytes const floatMaxIOU        =  {0x0D, 0xE0, 0xB6, 0xB3, 0xA7, 0x63, 0xFF, 0x9C, 0x00, 0x00, 0x00, 0x4E};  // 9999999999999999e(96)
-    Bytes const floatMinIOU        =  {0x0D, 0xE0, 0xB6, 0xB3, 0xA7, 0x64, 0x00, 0x00, 0xFF, 0xFF, 0xFF, 0x9D};  // 1e(-96 - 3 + normalExp = -81)
-
-    Bytes const float1             =  {0x0D, 0xE0, 0xB6, 0xB3, 0xA7, 0x64, 0x00, 0x00, 0xFF, 0xFF, 0xFF, 0xEE};  // 1
-    Bytes const floatMinus1        =  {0xF2, 0x1F, 0x49, 0x4C, 0x58, 0x9C, 0x00, 0x00, 0xFF, 0xFF, 0xFF, 0xEE};  // -1
-    Bytes const float1More         =  {0x0D, 0xE0, 0xB6, 0xB3, 0xA7, 0x64, 0x03, 0xE8, 0xFF, 0xFF, 0xFF, 0xEE};  // 1.000 000 000 000 001
-    Bytes const float2             =  {0x1B, 0xC1, 0x6D, 0x67, 0x4E, 0xC8, 0x00, 0x00, 0xFF, 0xFF, 0xFF, 0xEE};  // 2
-    Bytes const float10            =  {0x0D, 0xE0, 0xB6, 0xB3, 0xA7, 0x64, 0x00, 0x00, 0xFF, 0xFF, 0xFF, 0xEF};  // 10
-    Bytes const floatPi            =  {0x2B, 0x99, 0x2D, 0xDF, 0xA2, 0x32, 0x48, 0xE8, 0xFF, 0xFF, 0xFF, 0xEE};  // 3.141592653589793
-    Bytes const floatInvalidZero   =  {0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x81, 0x00, 0x00, 0x00};  // INVALID
-    Bytes const floatMinus3        =  {0xD6, 0x5D, 0xDB, 0xE5, 0x09, 0xD4, 0x00, 0x00, 0xFF, 0xFF, 0xFF, 0xEE};  // -3
+    Bytes const floatIntMin        =  {0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00,
+0x00, 0x00};  // -2^63 (rounds to nearest: -(2^63-1)) Bytes const floatIntZero       =  {0x00, 0x00,
+0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x80, 0x00, 0x00, 0x00};  // 0 Bytes const floatIntMax        =
+{0x7F, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x00, 0x00, 0x00, 0x00};  // 2^63-1 Bytes const
+floatUIntMax       =  {0x19, 0x99, 0x99, 0x99, 0x99, 0x99, 0x99, 0x9A, 0x00, 0x00, 0x00, 0x01};  //
+2^64-1
+
+    Bytes const floatMaxExp        =  {0x0D, 0xE0, 0xB6, 0xB3, 0xA7, 0x64, 0x00, 0x00, 0x00, 0x00,
+0x80, 0x00};  // 1e(Number::kMaxExponent + normalExp) Bytes const floatPreMaxExp     =  {0x0D, 0xE0,
+0xB6, 0xB3, 0xA7, 0x64, 0x00, 0x00, 0x00, 0x00, 0x7F, 0xFF};  // 1e(Number::kMaxExponent + normalExp
+- 1) Bytes const floatMinusMaxExp   =  {0xF2, 0x1F, 0x49, 0x4C, 0x58, 0x9C, 0x00, 0x00, 0x00, 0x00,
+0x80, 0x00};  // -1e(Number::kMaxExponent + normalExp) Bytes const floatMinExp        =  {0x00,
+0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x80, 0x00, 0x00, 0x00};  // 1e(Number::kMinExponent -
+normalExp) Bytes const floatMax           =  {0x7F, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x00,
+0x00, 0x80, 0x00};  // Number::kMaxRep e(Number::kMaxExponent - normalExp)
+
+    Bytes const floatMaxIOU        =  {0x0D, 0xE0, 0xB6, 0xB3, 0xA7, 0x63, 0xFF, 0x9C, 0x00, 0x00,
+0x00, 0x4E};  // 9999999999999999e(96) Bytes const floatMinIOU        =  {0x0D, 0xE0, 0xB6, 0xB3,
+0xA7, 0x64, 0x00, 0x00, 0xFF, 0xFF, 0xFF, 0x9D};  // 1e(-96 - 3 + normalExp = -81)
+
+    Bytes const float1             =  {0x0D, 0xE0, 0xB6, 0xB3, 0xA7, 0x64, 0x00, 0x00, 0xFF, 0xFF,
+0xFF, 0xEE};  // 1 Bytes const floatMinus1        =  {0xF2, 0x1F, 0x49, 0x4C, 0x58, 0x9C, 0x00,
+0x00, 0xFF, 0xFF, 0xFF, 0xEE};  // -1 Bytes const float1More         =  {0x0D, 0xE0, 0xB6, 0xB3,
+0xA7, 0x64, 0x03, 0xE8, 0xFF, 0xFF, 0xFF, 0xEE};  // 1.000 000 000 000 001 Bytes const float2 =
+{0x1B, 0xC1, 0x6D, 0x67, 0x4E, 0xC8, 0x00, 0x00, 0xFF, 0xFF, 0xFF, 0xEE};  // 2 Bytes const float10
+=  {0x0D, 0xE0, 0xB6, 0xB3, 0xA7, 0x64, 0x00, 0x00, 0xFF, 0xFF, 0xFF, 0xEF};  // 10 Bytes const
+floatPi            =  {0x2B, 0x99, 0x2D, 0xDF, 0xA2, 0x32, 0x48, 0xE8, 0xFF, 0xFF, 0xFF, 0xEE};
+// 3.141592653589793 Bytes const floatInvalidZero   =  {0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+0x00, 0x81, 0x00, 0x00, 0x00};  // INVALID Bytes const floatMinus3        =  {0xD6, 0x5D, 0xDB,
+0xE5, 0x09, 0xD4, 0x00, 0x00, 0xFF, 0xFF, 0xFF, 0xEE};  // -3
 
     std::string const invalid = "invalid_data";
 
@@ -6436,3 +6444,4 @@ struct HostFuncImpl_test : public beast::unit_test::Suite
 BEAST_DEFINE_TESTSUITE(HostFuncImpl, app, xrpl);
 
 }  // namespace xrpl::test
+*/
diff --git a/src/test/app/Wasm_test.cpp b/src/test/app/Wasm_test.cpp
index c2a493de42e..4f77df98b56 100644
--- a/src/test/app/Wasm_test.cpp
+++ b/src/test/app/Wasm_test.cpp
@@ -1,3 +1,10 @@
+// Not built. These suites drive a C++ wasm engine interface -- WasmVM over the wasm.h C API,
+// HostFuncWrapper, WasmImportsHelper -- that this tree does not provide; the VM lives in the
+// Rust crates. Kept as the coverage target for the port. The body is one comment block, and
+// the fixtures it reads (wasm_fixtures/fixtures.cpp) are disabled the same way; re-enabling
+// the suites means uncommenting both.
+
+/*
 #include <expected>
 #ifdef _DEBUG
 // #define DEBUG_OUTPUT 1
@@ -78,32 +85,32 @@ struct Wasm_test : public beast::unit_test::Suite
     {
         testcase("wasm lib test");
         // clang-format off
-        /* The WASM module buffer. */
-        Bytes const wasm = {/* WASM header */
+        // The WASM module buffer. //
+        Bytes const wasm = {// WASM header //
                           0x00, 0x61, 0x73, 0x6D, 0x01, 0x00, 0x00, 0x00,
-                          /* Type section */
+                          // Type section //
                           0x01, 0x07, 0x01,
-                          /* function type {i32, i32} -> {i32} */
+                          // function type {i32, i32} -> {i32} //
                           0x60, 0x02, 0x7F, 0x7F, 0x01, 0x7F,
-                          /* Import section */
+                          // Import section //
                           0x02, 0x13, 0x01,
-                          /* module name: "extern" */
+                          // module name: "extern" //
                           0x06, 0x65, 0x78, 0x74, 0x65, 0x72, 0x6E,
-                          /* extern name: "func-add" */
+                          // extern name: "func-add" //
                           0x08, 0x66, 0x75, 0x6E, 0x63, 0x2D, 0x61, 0x64, 0x64,
-                          /* import desc: func 0 */
+                          // import desc: func 0 //
                           0x00, 0x00,
-                          /* Function section */
+                          // Function section //
                           0x03, 0x02, 0x01, 0x00,
-                          /* Export section */
+                          // Export section //
                           0x07, 0x0A, 0x01,
-                          /* export name: "addTwo" */
+                          // export name: "addTwo" //
                           0x06, 0x61, 0x64, 0x64, 0x54, 0x77, 0x6F,
-                          /* export desc: func 0 */
+                          // export desc: func 0 //
                           0x00, 0x01,
-                          /* Code section */
+                          // Code section //
                           0x0A, 0x0A, 0x01,
-                          /* code body */
+                          // code body //
                           0x08, 0x00, 0x20, 0x00, 0x20, 0x01, 0x10, 0x00, 0x0B};
         // clang-format on
         auto& vm = WasmEngine::instance();
@@ -467,3 +474,4 @@ struct Wasm_test : public beast::unit_test::Suite
 BEAST_DEFINE_TESTSUITE(Wasm, app, xrpl);
 
 }  // namespace xrpl::test
+*/
diff --git a/src/test/app/wasm_fixtures/fixtures.cpp b/src/test/app/wasm_fixtures/fixtures.cpp
index 363da88f8d9..53b0d90be07 100644
--- a/src/test/app/wasm_fixtures/fixtures.cpp
+++ b/src/test/app/wasm_fixtures/fixtures.cpp
@@ -1,5 +1,10 @@
+// Not built. The only reader of these blobs is the disabled suite in Wasm_test.cpp, so they
+// are left out of the build and cost neither a translation unit nor static-init time.
+// Regenerate the hex with copyFixtures.py.
+//
 // TODO: consider moving these to separate files (and figure out the build)
 
+/*
 #include <test/app/wasm_fixtures/fixtures.h>
 
 #include <string>
@@ -649,3 +654,4 @@ extern std::string const kBadAlignWasmHex =
     "32393538616631656533303861373930636664623432626432343732302900490f7461726765745f66656174757265"
     "73042b0f6d757461626c652d676c6f62616c732b087369676e2d6578742b0f7265666572656e63652d74797065732b"
     "0a6d756c746976616c7565";
+*/
diff --git a/src/tests/libxrpl/CMakeLists.txt b/src/tests/libxrpl/CMakeLists.txt
index 5e4cda243aa..e4121bc92c4 100644
--- a/src/tests/libxrpl/CMakeLists.txt
+++ b/src/tests/libxrpl/CMakeLists.txt
@@ -23,6 +23,11 @@ set_target_properties(
 target_include_directories(xrpl_tests PRIVATE ${CMAKE_CURRENT_SOURCE_DIR})
 target_link_libraries(xrpl_tests PRIVATE GTest::gtest GTest::gmock xrpl.libxrpl)
 
+# Lets the wasm tests write their modules as WebAssembly text. Test-only by construction:
+# the assembler lives in a crate nothing in libxrpl or xrpld links (see crates/CMakeLists).
+target_link_libraries(xrpl_tests PRIVATE xrpl_wasm_testkit_cxxbridge)
+add_dependencies(xrpl_tests xrpl_crates)
+
 # One source subdirectory per module. Network unit tests are currently not
 # supported on Windows.
 set(test_modules
diff --git a/src/tests/libxrpl/tx/wasm/MockHostFunctions.h b/src/tests/libxrpl/tx/wasm/MockHostFunctions.h
new file mode 100644
index 00000000000..d75291cc9a9
--- /dev/null
+++ b/src/tests/libxrpl/tx/wasm/MockHostFunctions.h
@@ -0,0 +1,66 @@
+#pragma once
+
+#include <xrpl/basics/Slice.h>
+#include <xrpl/beast/utility/Journal.h>
+#include <xrpl/protocol/SField.h>
+#include <xrpl/tx/wasm/HostFunc.h>
+#include <xrpl/tx/wasm/WasmCommon.h>
+
+#include <gmock/gmock.h>
+
+#include <cstdint>
+#include <expected>
+#include <string_view>
+
+namespace xrpl::test {
+
+// A mock of the host the wasm engine calls back into.
+//
+// Only the methods the ABI currently declares are mocked, and that is deliberate: the ~60
+// others keep `HostFunctions`' own `std::unexpected(Unimplemented)`, so a contract reaching
+// for something the ABI has not declared yet fails the way production would. Add a
+// `MOCK_METHOD` here when the matching entry is added to `host_functions!`.
+struct MockHostFunctions : HostFunctions
+{
+    explicit MockHostFunctions(beast::Journal journal) : HostFunctions(journal)
+    {
+    }
+
+    MOCK_METHOD(bool, checkSelf, (), (const, override));
+
+    MOCK_METHOD(
+        (std::expected<std::uint32_t, HostFunctionError>),
+        getLedgerSqn,
+        (),
+        (const, override));
+
+    MOCK_METHOD(
+        (std::expected<Bytes, HostFunctionError>),
+        getCurrentLedgerObjField,
+        (SField const& fname),
+        (const, override));
+
+    MOCK_METHOD(
+        (std::expected<Hash, HostFunctionError>),
+        computeSha512HalfHash,
+        (Slice const& data),
+        (const, override));
+
+    // Takes the rendered text, not the guest's buffer: rendering is `HostContext`'s, so what
+    // a test asserts here is the log line a node would write.
+    MOCK_METHOD(
+        void,
+        trace,
+        (std::string_view const& msg, std::string_view const& data),
+        (const, override));
+};
+
+// Matches a `Slice` (or anything with `data()`/`size()`) against the bytes of a string, so
+// an expectation can say *what* the guest asked the host to work on.
+MATCHER_P(BytesAre, expected, "")
+{
+    return std::string_view{reinterpret_cast<char const*>(arg.data()), arg.size()} ==
+        std::string_view{expected};
+}
+
+}  // namespace xrpl::test
diff --git a/src/tests/libxrpl/tx/wasm/Preflight.cpp b/src/tests/libxrpl/tx/wasm/Preflight.cpp
new file mode 100644
index 00000000000..0391f097115
--- /dev/null
+++ b/src/tests/libxrpl/tx/wasm/Preflight.cpp
@@ -0,0 +1,223 @@
+#include <xrpl/beast/utility/Journal.h>
+#include <xrpl/protocol/TER.h>
+#include <xrpl/tx/wasm/WasmCommon.h>
+#include <xrpl/tx/wasm/WasmVM.h>
+
+#include <gmock/gmock.h>
+#include <gtest/gtest.h>
+#include <helpers/CaptureSink.h>
+#include <tx/wasm/MockHostFunctions.h>
+#include <tx/wasm/WasmFixture.h>
+
+#include <string>
+#include <string_view>
+
+namespace xrpl::test {
+
+namespace {
+
+// A contract the engine can run: it compiles, imports only a declared host function, and
+// exports the entry point as `() -> i32`.
+constexpr std::string_view kRunnableWat = R"wat(
+(module
+  (import "host_lib" "ldgr_index" (func $ldgr_index (param i32 i32) (result i32)))
+  (memory (export "memory") 1)
+  (func (export "escrow_finish") (result i32)
+    (call $ldgr_index (i32.const 0) (i32.const 4))))
+)wat";
+
+}  // namespace
+
+// `preflightEscrowWasm` takes no host, so this fixture holds none - which is the point of
+// the signature, and what deriving from `WasmTest` would hide. Only a journal, to read the
+// refusal out of.
+struct PreflightTest : testing::Test
+{
+    CaptureSink sink{beast::Severity::Warning};
+
+    NotTEC
+    preflight(std::string_view wat, std::string_view funcName = escrowFunctionName)
+    {
+        return preflightEscrowWasm(assembleWat(wat), beast::Journal{sink}, funcName);
+    }
+
+    NotTEC
+    preflightBytes(Bytes const& wasm, std::string_view funcName = escrowFunctionName)
+    {
+        return preflightEscrowWasm(wasm, beast::Journal{sink}, funcName);
+    }
+
+    [[nodiscard]] std::string
+    logged() const
+    {
+        return sink.messages();
+    }
+};
+
+TEST_F(PreflightTest, RunnableContractPasses)
+{
+    EXPECT_EQ(preflight(kRunnableWat), tesSUCCESS);
+    EXPECT_TRUE(logged().empty()) << logged();
+}
+
+TEST_F(PreflightTest, GarbageIsRefused)
+{
+    EXPECT_EQ(preflightBytes(Bytes{}), temBAD_WASM);
+    EXPECT_EQ(preflightBytes(Bytes{0x00, 0x61, 0x73, 0x6d}), temBAD_WASM);
+}
+
+// The engine takes wasm binaries, and text is not one. The suite writes its modules as text
+// and assembles them, so this feeds the engine the very text the other tests assemble: a
+// transaction's validity must not depend on whether an assembler was linked in.
+TEST_F(PreflightTest, TextFormatModuleIsRefused)
+{
+    Bytes const text{kRunnableWat.begin(), kRunnableWat.end()};
+
+    EXPECT_EQ(preflightBytes(text), temBAD_WASM);
+    EXPECT_EQ(preflight(kRunnableWat), tesSUCCESS) << "the same module, assembled first";
+}
+
+TEST_F(PreflightTest, ImportOfAnUnknownHostFunctionIsRefused)
+{
+    constexpr std::string_view wat = R"wat(
+    (module
+      (import "host_lib" "no_such_function" (func $f (param i32) (result i32)))
+      (memory (export "memory") 1)
+      (func (export "escrow_finish") (result i32) (call $f (i32.const 0))))
+    )wat";
+
+    EXPECT_EQ(preflight(wat), temBAD_WASM);
+    EXPECT_THAT(logged(), testing::HasSubstr("no host function 'no_such_function'"));
+}
+
+// Host functions are registered under one module name. `env` is what plain clang emits, so a
+// contract built without the SDK's import attributes lands here.
+TEST_F(PreflightTest, ImportFromAnotherModuleIsRefused)
+{
+    constexpr std::string_view wat = R"wat(
+    (module
+      (import "env" "ldgr_index" (func $f (param i32 i32) (result i32)))
+      (memory (export "memory") 1)
+      (func (export "escrow_finish") (result i32) (i32.const 0)))
+    )wat";
+
+    EXPECT_EQ(preflight(wat), temBAD_WASM);
+    EXPECT_THAT(logged(), testing::HasSubstr("is not from 'host_lib'"));
+}
+
+// A contract asking for more linear memory than the engine grants can never run, so it is
+// refused before it can be escrowed. The cap itself is granted.
+TEST_F(PreflightTest, MemoryPastTheCapIsRefused)
+{
+    constexpr std::string_view tooMuch = R"wat(
+    (module
+      (memory (export "memory") 129)
+      (func (export "escrow_finish") (result i32) (i32.const 0)))
+    )wat";
+
+    EXPECT_EQ(preflight(tooMuch), temBAD_WASM);
+    EXPECT_THAT(logged(), testing::HasSubstr("memory: initial memory of 129 pages"));
+
+    constexpr std::string_view atTheCap = R"wat(
+    (module
+      (memory (export "memory") 128)
+      (func (export "escrow_finish") (result i32) (i32.const 0)))
+    )wat";
+
+    EXPECT_EQ(preflight(atTheCap), tesSUCCESS);
+}
+
+TEST_F(PreflightTest, MissingEntryPointIsRefused)
+{
+    constexpr std::string_view wat = R"wat(
+    (module
+      (memory (export "memory") 1)
+      (func (export "other") (result i32) (i32.const 0)))
+    )wat";
+
+    EXPECT_EQ(preflight(wat), temBAD_WASM);
+    EXPECT_THAT(logged(), testing::HasSubstr("no entry point 'escrow_finish'"));
+}
+
+TEST_F(PreflightTest, EntryPointOfTheWrongTypeIsRefused)
+{
+    constexpr std::string_view wat = R"wat(
+    (module
+      (memory (export "memory") 1)
+      (func (export "escrow_finish") (result i64) (i64.const 0)))
+    )wat";
+
+    EXPECT_EQ(preflight(wat), temBAD_WASM);
+    EXPECT_THAT(logged(), testing::HasSubstr("has the wrong signature"));
+}
+
+// Screening is for the entry point the caller names, as a run is: a contract screened for one
+// export says nothing about another.
+TEST_F(PreflightTest, EntryPointIsTheNameTheCallerGives)
+{
+    constexpr std::string_view wat = R"wat(
+    (module
+      (memory (export "memory") 1)
+      (func (export "other") (result i32) (i32.const 0)))
+    )wat";
+
+    EXPECT_EQ(preflight(wat, "other"), tesSUCCESS);
+    EXPECT_EQ(preflight(wat), temBAD_WASM);
+}
+
+// Every refusal is logged with the engine's own description and the TER: without it a node
+// operator has a `temBAD_WASM` and no way to tell a contract author which of the three
+// stages refused the module.
+TEST_F(PreflightTest, RefusalNamesTheReasonAndTheTer)
+{
+    EXPECT_EQ(preflightBytes(Bytes{0x00, 0x61, 0x73, 0x6d}), temBAD_WASM);
+
+    EXPECT_THAT(logged(), testing::HasSubstr("compile: "));
+    EXPECT_THAT(logged(), testing::HasSubstr(transToken(temBAD_WASM)));
+}
+
+// A module that passes screening still has to pass the run's own stages, and one that fails
+// screening would have failed the run. Same modules through both entry points, so the two do
+// not have to be trusted to agree.
+TEST_F(PreflightTest, ScreeningAgreesWithARun)
+{
+    struct Case
+    {
+        std::string_view label;
+        std::string_view wat;
+        bool passes;
+    };
+
+    // clang-format off
+    constexpr Case cases[]{
+        {.label = "a runnable contract", .wat = kRunnableWat, .passes = true},
+        {.label = "an unknown host function",
+         .wat = R"wat((module (import "host_lib" "nope" (func $f (result i32)))
+                        (memory (export "memory") 1)
+                        (func (export "escrow_finish") (result i32) (call $f))))wat",
+         .passes = false},
+        {.label = "no entry point",
+         .wat = R"wat((module (memory (export "memory") 1)
+                        (func (export "other") (result i32) (i32.const 0))))wat",
+         .passes = false},
+    };
+    // clang-format on
+
+    for (auto const& [label, wat, passes] : cases)
+    {
+        auto const screened = preflight(wat);
+        EXPECT_EQ(isTesSuccess(screened), passes) << label;
+
+        // The run's own verdict on the same bytes. A refused module must not reach the
+        // contract's first instruction; an accepted one must get past the entry-point
+        // lookup, whatever it then does.
+        testing::StrictMock<MockHostFunctions> host{beast::Journal{sink}};
+        EXPECT_CALL(host, checkSelf()).WillRepeatedly(testing::Return(true));
+        EXPECT_CALL(host, getLedgerSqn()).WillRepeatedly(testing::Return(7u));
+
+        auto const ran = runEscrowWasm(assembleWat(wat), host, 100'000);
+        EXPECT_EQ(ran.has_value(), passes) << label;
+    }
+}
+
+}  // namespace xrpl::test
diff --git a/src/tests/libxrpl/tx/wasm/WasmFixture.h b/src/tests/libxrpl/tx/wasm/WasmFixture.h
new file mode 100644
index 00000000000..662752806e6
--- /dev/null
+++ b/src/tests/libxrpl/tx/wasm/WasmFixture.h
@@ -0,0 +1,124 @@
+#pragma once
+
+#include <xrpl/beast/utility/Journal.h>
+#include <xrpl/protocol/TER.h>
+#include <xrpl/tx/wasm/WasmCommon.h>
+#include <xrpl/tx/wasm/WasmVM.h>
+
+#include <gmock/gmock.h>
+#include <gtest/gtest.h>
+#include <helpers/CaptureSink.h>
+#include <tx/wasm/MockHostFunctions.h>
+#include <xrpl_wasm_testkit_cxxbridge/lib.h>
+
+#include <cstdint>
+#include <expected>
+#include <string>
+#include <string_view>
+
+namespace xrpl::test {
+
+// Assemble `wat`. Throws `rust::Error` on a typo, which gtest reports against the test that
+// holds it.
+//
+// A free function because not every wasm test needs a host: `preflightEscrowWasm` takes none,
+// so its fixture derives from `testing::Test` rather than from `WasmTest`.
+inline Bytes
+assembleWat(std::string_view wat)
+{
+    auto const wasm = rs::wasm_testkit::compile_wat(rust::Str{wat.data(), wat.size()});
+    return Bytes{wasm.begin(), wasm.end()};
+}
+
+// Base for every wasm test that runs a contract: a mocked host whose log is captured, and one
+// way into the engine.
+//
+// Modules are written as WebAssembly text and assembled by `assembleWat`. The assembler is in
+// a test-only crate: the engine itself refuses text
+// (`the_vm_refuses_a_text_format_module`), because a text assembler on the consensus path
+// would make a transaction's validity a build flag.
+struct WasmTest : testing::Test
+{
+    // Enough for every module here to run to completion; a test about budgets passes its own.
+    static constexpr std::int64_t kAmpleGas = 100'000;
+
+    // Keeps what a run logged. The host's default journal is a null sink, which would let a
+    // swallowed condition pass a test that only checks the TER.
+    CaptureSink sink{beast::Severity::Warning};
+
+    // Strict: a host call no test asked for is a failure, not a warning. These modules import
+    // exactly what they mean to exercise, so an unplanned call means the engine reached for
+    // something on its own — which is the kind of surprise a test suite exists to catch.
+    testing::StrictMock<MockHostFunctions> host{beast::Journal{sink}};
+
+    WasmTest()
+    {
+        // `runEscrowWasm` asks every run whether the host is clean, so under a strict mock
+        // every test would have to say so. Declared once here, and any number of times
+        // (including none, for the runs refused before the engine is reached). A test that
+        // cares says otherwise and its own expectation wins.
+        EXPECT_CALL(host, checkSelf()).WillRepeatedly(testing::Return(true));
+    }
+
+    static Bytes
+    assemble(std::string_view wat)
+    {
+        return assembleWat(wat);
+    }
+
+    std::expected<EscrowResult, WasmTER>
+    run(std::string_view wat,
+        std::int64_t gas = kAmpleGas,
+        std::string_view entryPoint = escrowFunctionName)
+    {
+        return runEscrowWasm(assemble(wat), host, gas, entryPoint);
+    }
+
+    std::expected<EscrowResult, WasmTER>
+    runBytes(
+        Bytes const& wasm,
+        std::int64_t gas = kAmpleGas,
+        std::string_view entryPoint = escrowFunctionName)
+    {
+        return runEscrowWasm(wasm, host, gas, entryPoint);
+    }
+
+    [[nodiscard]] std::string
+    logged() const
+    {
+        return sink.messages();
+    }
+};
+
+// Base for the per-host-function fixtures. Each derives, supplies the module that exercises
+// its own import, and runs it through `callHost()` — so a test says only what the host was
+// asked and what came back.
+struct HostCallTest : WasmTest
+{
+    // The module under test. One import, one `escrow_finish` that calls it.
+    [[nodiscard]] virtual std::string
+    wat() const = 0;
+
+    std::expected<EscrowResult, WasmTER>
+    callHost(std::string_view entryPoint = escrowFunctionName)
+    {
+        return run(wat(), kAmpleGas, entryPoint);
+    }
+
+    // The contract's return value, which for these modules is what the host answered — or
+    // its negative error code. Fails the test if the run did not complete.
+    std::int32_t
+    hostAnswer(std::string_view entryPoint = escrowFunctionName)
+    {
+        auto const outcome = callHost(entryPoint);
+        if (!outcome)
+        {
+            ADD_FAILURE() << "the run did not complete: " << transToken(outcome.error().ter)
+                          << "; logged: " << logged();
+            return 0;
+        }
+        return outcome->result;
+    }
+};
+
+}  // namespace xrpl::test
diff --git a/src/tests/libxrpl/tx/wasm/WasmVM.cpp b/src/tests/libxrpl/tx/wasm/WasmVM.cpp
new file mode 100644
index 00000000000..76c774e3ebc
--- /dev/null
+++ b/src/tests/libxrpl/tx/wasm/WasmVM.cpp
@@ -0,0 +1,325 @@
+#include <xrpl/tx/wasm/WasmVM.h>
+
+#include <xrpl/basics/contract.h>
+#include <xrpl/protocol/TER.h>
+#include <xrpl/tx/wasm/WasmCommon.h>
+
+#include <gmock/gmock.h>
+#include <gtest/gtest.h>
+#include <tx/wasm/WasmFixture.h>
+
+#include <array>
+#include <cstdint>
+#include <expected>
+#include <stdexcept>
+#include <string>
+#include <string_view>
+
+namespace xrpl::test {
+
+namespace {
+
+// One module with an export per way a run can end. Kept together because these are properties
+// of the engine rather than of any host function: the only import is there so the
+// out-of-gas and no-memory cases have a host call to fail in.
+constexpr std::string_view kEngineWat = R"wat(
+(module
+  (import "host_lib" "ldgr_index" (func $ldgr_index (param i32 i32) (result i32)))
+  (memory (export "memory") 1)
+
+  (func (export "escrow_finish") (result i32) (i32.const 5))
+
+  (func (export "calls_the_host") (result i32)
+    (call $ldgr_index (i32.const 0) (i32.const 4)))
+
+  (func (export "traps") (result i32) unreachable)
+
+  (func (export "never_returns") (result i32) (loop (br 0)) (i32.const 0))
+
+  (func (export "wrong_signature") (param i32) (result i32) (local.get 0))
+
+  (global (export "not_a_function") i32 (i32.const 0)))
+)wat";
+
+// The same host call with no memory exported, so the engine has nothing to resolve a byte
+// region against.
+constexpr std::string_view kNoMemoryWat = R"wat(
+(module
+  (import "host_lib" "ldgr_index" (func $ldgr_index (param i32 i32) (result i32)))
+  (func (export "escrow_finish") (result i32)
+    (call $ldgr_index (i32.const 0) (i32.const 4))))
+)wat";
+
+}  // namespace
+
+class WasmVMTest : public WasmTest
+{
+};
+
+TEST_F(WasmVMTest, ContractReturnValueReachesCaller)
+{
+    auto const outcome = run(kEngineWat);
+
+    ASSERT_TRUE(outcome.has_value()) << transToken(outcome.error().ter);
+    EXPECT_EQ(outcome->result, 5);
+    EXPECT_GT(outcome->cost, 0) << "running any instruction costs gas";
+    EXPECT_LT(outcome->cost, kAmpleGas);
+}
+
+TEST_F(WasmVMTest, GuestTrapIsChargedAsContractFault)
+{
+    auto const outcome = run(kEngineWat, kAmpleGas, "traps");
+
+    ASSERT_FALSE(outcome.has_value());
+    EXPECT_EQ(outcome.error().ter, tecFAILED_PROCESSING);
+    ASSERT_TRUE(outcome.error().cost.has_value());
+    EXPECT_GT(*outcome.error().cost, 0);  // NOLINT(bugprone-unchecked-optional-access)
+}
+
+TEST_F(WasmVMTest, NonTerminatingContractSpendsWholeBudget)
+{
+    auto const outcome = run(kEngineWat, kAmpleGas, "never_returns");
+
+    ASSERT_FALSE(outcome.has_value());
+    EXPECT_EQ(outcome.error().ter, tecOUT_OF_GAS);
+    ASSERT_TRUE(outcome.error().cost.has_value());
+    EXPECT_EQ(*outcome.error().cost, kAmpleGas);  // NOLINT(bugprone-unchecked-optional-access)
+}
+
+// A budget too small to reach the first host charge is still out of gas, whatever the engine
+// can account for by then.
+TEST_F(WasmVMTest, BudgetTooSmallToRunIsOutOfGas)
+{
+    auto const outcome = run(kEngineWat, 1, "calls_the_host");
+
+    ASSERT_FALSE(outcome.has_value());
+    EXPECT_EQ(outcome.error().ter, tecOUT_OF_GAS);
+    EXPECT_TRUE(outcome.error().cost.has_value());
+}
+
+// No gas is not a small budget, it is a malformed transaction — refused before the engine is
+// asked to run anything.
+TEST_F(WasmVMTest, NoGasIsRefusedAsMalformedRatherThanRun)
+{
+    for (auto const gas : {std::int64_t{0}, std::int64_t{-1}})
+    {
+        auto const outcome = run(kEngineWat, gas);
+
+        ASSERT_FALSE(outcome.has_value()) << "gas: " << gas;
+        EXPECT_EQ(outcome.error().ter, temBAD_AMOUNT) << "gas: " << gas;
+        EXPECT_FALSE(outcome.error().cost.has_value()) << "gas: " << gas;
+    }
+}
+
+// A host call needs a memory to resolve its byte regions against, and the export is not
+// optional for a contract that makes one.
+TEST_F(WasmVMTest, HostCallWithNoExportedMemoryFails)
+{
+    auto const outcome = run(kNoMemoryWat);
+
+    ASSERT_FALSE(outcome.has_value());
+    EXPECT_EQ(outcome.error().ter, tecFAILED_PROCESSING);
+    EXPECT_TRUE(outcome.error().cost.has_value());
+}
+
+// A module that will not instantiate is the contract's fault and is charged, not the node's.
+// Screening does not see every way this happens - a linear memory the module keeps to itself
+// is absent from its exports - so such a module can pass preflight and still be refused here.
+TEST_F(WasmVMTest, ModuleThatWillNotInstantiateIsChargedToTheContract)
+{
+    // 129 pages, not exported, so nothing outside the module declares it.
+    static constexpr std::string_view wat = R"wat(
+    (module
+      (memory 129)
+      (func (export "escrow_finish") (result i32) (i32.const 0)))
+    )wat";
+
+    EXPECT_EQ(preflightEscrowWasm(assembleWat(wat), beast::Journal{sink}), tesSUCCESS)
+        << "screening cannot see an unexported memory";
+
+    auto const outcome = run(wat);
+
+    ASSERT_FALSE(outcome.has_value());
+    EXPECT_EQ(outcome.error().ter, tecFAILED_PROCESSING);
+    EXPECT_TRUE(outcome.error().cost.has_value());
+}
+
+// A start section is guest code, so a trap in one is the contract's fault wherever it
+// happens - charged for what it burned, rather than reported as a module the node should
+// have screened.
+TEST_F(WasmVMTest, TrappingStartSectionIsChargedToTheContract)
+{
+    static constexpr std::string_view wat = R"wat(
+    (module
+      (memory (export "memory") 1)
+      (func $init (unreachable))
+      (start $init)
+      (func (export "escrow_finish") (result i32) (i32.const 0)))
+    )wat";
+
+    auto const outcome = run(wat);
+
+    ASSERT_FALSE(outcome.has_value());
+    EXPECT_EQ(outcome.error().ter, tecFAILED_PROCESSING);
+    ASSERT_TRUE(outcome.error().cost.has_value());
+    // NOLINTNEXTLINE(bugprone-unchecked-optional-access)
+    EXPECT_GT(*outcome.error().cost, 0) << "the start section's instructions are metered";
+}
+
+// Preflight is meant to refuse these with `temBAD_WASM`; reaching apply means the screening
+// did not happen, which is the node's fault and not the transaction's.
+TEST_F(WasmVMTest, UnrunnableModuleIsNodeSideFault)
+{
+    struct Case
+    {
+        char const* what;
+        Bytes code;
+        std::string_view entryPoint;
+    };
+    std::array const cases = {
+        Case{
+            .what = "not wasm at all", .code = Bytes{0, 1, 2, 3}, .entryPoint = escrowFunctionName},
+        Case{.what = "empty", .code = Bytes{}, .entryPoint = escrowFunctionName},
+        Case{
+            .what = "no such export", .code = assemble(kEngineWat), .entryPoint = "no_such_export"},
+        Case{
+            .what = "export is not a function",
+            .code = assemble(kEngineWat),
+            .entryPoint = "not_a_function"},
+        Case{
+            .what = "export takes a parameter",
+            .code = assemble(kEngineWat),
+            .entryPoint = "wrong_signature"},
+    };
+
+    for (auto const& c : cases)
+    {
+        auto const outcome = runBytes(c.code, kAmpleGas, c.entryPoint);
+
+        ASSERT_FALSE(outcome.has_value()) << c.what;
+        EXPECT_EQ(outcome.error().ter, tecINTERNAL) << c.what;
+        EXPECT_FALSE(outcome.error().cost.has_value()) << c.what;
+    }
+}
+
+// wasmi's `wat` feature would make `Module::new` accept text as readily as binary, which would
+// put an assembler on the consensus path and make a module's validity a build flag. The
+// engine turns that feature off; this is the guest-side proof, using the very text the rest
+// of this file assembles.
+TEST_F(WasmVMTest, TextFormatModuleIsRejected)
+{
+    Bytes const text{kEngineWat.begin(), kEngineWat.end()};
+
+    auto const outcome = runBytes(text);
+
+    ASSERT_FALSE(outcome.has_value());
+    EXPECT_EQ(outcome.error().ter, tecINTERNAL);
+}
+
+// The host caches the current ledger object, the slot table and the contract's data for the
+// length of one run, so a reused one would answer a later contract out of an earlier
+// contract's state.
+TEST_F(WasmVMTest, DirtyHostIsRefusedBeforeContractRuns)
+{
+    EXPECT_CALL(host, checkSelf()).WillOnce(testing::Return(false));
+
+    auto const outcome = run(kEngineWat);
+
+    ASSERT_FALSE(outcome.has_value());
+    EXPECT_EQ(outcome.error().ter, tecINTERNAL);
+    EXPECT_FALSE(outcome.error().cost.has_value());
+    EXPECT_THAT(logged(), testing::HasSubstr("not clean"));
+}
+
+// A soft host error is the contract's to interpret, so its code has to cross the boundary
+// unchanged: the engine must not renumber it, clamp it, or turn it into a failure of its own.
+//
+// Over the whole of `HostFunctionError` rather than a sample, because the C++ and Rust error
+// enums are two hand-maintained lists of the same wire numbers and they have already drifted
+// once — C++ spells -11 `OutOfTransferLimit` where the Rust ABI spells it `Decoding`. This is
+// the test that notices if either side renumbers.
+//
+// The two exclusions are the codes the Rust engine treats as host-fatal, which stop the run
+// instead of reaching the guest: -1 (its `Internal`, which C++ spells `Unimplemented`) and
+// -14 `NoMemExported`.
+TEST_F(WasmVMTest, SoftHostErrorCodesCrossUnchanged)
+{
+    static constexpr HostFunctionError kSoftErrors[] = {
+        HostFunctionError::FieldNotFound,
+        HostFunctionError::BufferTooSmall,
+        HostFunctionError::NoArray,
+        HostFunctionError::NotLeafField,
+        HostFunctionError::LocatorMalformed,
+        HostFunctionError::SlotOutRange,
+        HostFunctionError::SlotsFull,
+        HostFunctionError::EmptySlot,
+        HostFunctionError::LedgerObjNotFound,
+        HostFunctionError::OutOfTransferLimit,
+        HostFunctionError::DataFieldTooLarge,
+        HostFunctionError::PointerOutOfBounds,
+        HostFunctionError::InvalidParams,
+        HostFunctionError::InvalidAccount,
+        HostFunctionError::InvalidField,
+        HostFunctionError::IndexOutOfBounds,
+        HostFunctionError::FloatInputMalformed,
+        HostFunctionError::FloatComputationError,
+    };
+
+    auto refused = HostFunctionError::FieldNotFound;
+    EXPECT_CALL(host, getLedgerSqn())
+        .WillRepeatedly([&refused]() -> std::expected<std::uint32_t, HostFunctionError> {
+            return std::unexpected(refused);
+        });
+
+    for (auto const error : kSoftErrors)
+    {
+        refused = error;
+
+        auto const outcome = run(kEngineWat, kAmpleGas, "calls_the_host");
+
+        ASSERT_TRUE(outcome.has_value()) << hfErrorToInt(error) << " stopped the run";
+        EXPECT_EQ(outcome->result, hfErrorToInt(error));
+    }
+}
+
+// The counterpart: a fatal code stops the run rather than reaching the contract, so a host
+// that cannot serve a call cannot be second-guessed by the contract.
+TEST_F(WasmVMTest, FatalHostErrorStopsRun)
+{
+    auto refused = HostFunctionError::Unimplemented;
+    EXPECT_CALL(host, getLedgerSqn())
+        .WillRepeatedly([&refused]() -> std::expected<std::uint32_t, HostFunctionError> {
+            return std::unexpected(refused);
+        });
+
+    for (auto const error : {HostFunctionError::Unimplemented, HostFunctionError::NoMemExported})
+    {
+        refused = error;
+
+        auto const outcome = run(kEngineWat, kAmpleGas, "calls_the_host");
+
+        ASSERT_FALSE(outcome.has_value()) << hfErrorToInt(error) << " reached the contract";
+    }
+}
+
+// The point of the bridge's C++ half: an exception must not reach the Rust frames that called
+// the host, and must not take the node with it.
+TEST_F(WasmVMTest, ThrowingHostFunctionBecomesInternal)
+{
+    EXPECT_CALL(host, getLedgerSqn())
+        .WillOnce([]() -> std::expected<std::uint32_t, HostFunctionError> {
+            Throw<std::runtime_error>("the ledger came apart");
+        });
+
+    auto const outcome = run(kEngineWat, kAmpleGas, "calls_the_host");
+
+    ASSERT_FALSE(outcome.has_value());
+    EXPECT_EQ(outcome.error().ter, tecINTERNAL);
+    EXPECT_FALSE(outcome.error().cost.has_value()) << "a node-side fault charges nothing";
+    // Caught is not swallowed: the condition has to be recorded, and the line has to name the
+    // call it came out of.
+    EXPECT_THAT(logged(), testing::HasSubstr("the ledger came apart"));
+    EXPECT_THAT(logged(), testing::HasSubstr("getLedgerSqn"));
+}
+
+}  // namespace xrpl::test
diff --git a/src/tests/libxrpl/tx/wasm/host_calls/CurrentLedgerObjField.cpp b/src/tests/libxrpl/tx/wasm/host_calls/CurrentLedgerObjField.cpp
new file mode 100644
index 00000000000..143c20fa969
--- /dev/null
+++ b/src/tests/libxrpl/tx/wasm/host_calls/CurrentLedgerObjField.cpp
@@ -0,0 +1,74 @@
+#include <xrpl/protocol/Protocol.h>
+#include <xrpl/protocol/SField.h>
+#include <xrpl/tx/wasm/WasmCommon.h>
+
+#include <gmock/gmock.h>
+#include <gtest/gtest.h>
+#include <tx/wasm/WasmFixture.h>
+
+#include <cstdint>
+#include <expected>
+#include <string>
+
+namespace xrpl::test {
+
+using testing::Return;
+
+// home_le_field — a scalar field code in, bytes out.
+struct CurrentLedgerObjFieldCall : HostCallTest
+{
+    // The field code the guest asks for. A real one, so the shim's `SField` lookup has
+    // something to find.
+    std::int32_t fieldCode = sfBalance.getCode();
+
+    [[nodiscard]] std::string
+    wat() const override
+    {
+        return std::string{R"wat(
+(module
+  (import "host_lib" "home_le_field" (func $home_le_field (param i32 i32 i32) (result i32)))
+  (memory (export "memory") 1)
+  (func (export "escrow_finish") (result i32)
+    (call $home_le_field (i32.const )wat"} +
+            std::to_string(fieldCode) + R"wat() (i32.const 0) (i32.const 32))))
+)wat";
+    }
+};
+
+// The shim turns the guest's `i32` into the `SField` the C++ interface takes; asserting on
+// the argument is what pins that translation rather than assuming it.
+TEST_F(CurrentLedgerObjFieldCall, FieldCodeBecomesSFieldHostIsAskedFor)
+{
+    EXPECT_CALL(host, getCurrentLedgerObjField(testing::Ref(sfBalance)))
+        .WillOnce(Return(Bytes{1, 2, 3}));
+
+    EXPECT_EQ(hostAnswer(), 3) << "the length the host reported";
+}
+
+TEST_F(CurrentLedgerObjFieldCall, UnknownFieldCodeIsRefusedWithoutAskingHost)
+{
+    fieldCode = 0x7fff'0000;  // a type nothing is registered under
+    EXPECT_CALL(host, getCurrentLedgerObjField).Times(0);
+
+    EXPECT_EQ(hostAnswer(), hfErrorToInt(HostFunctionError::InvalidField));
+}
+
+TEST_F(CurrentLedgerObjFieldCall, HostErrorBecomesContractReturnValue)
+{
+    EXPECT_CALL(host, getCurrentLedgerObjField)
+        .WillOnce(Return(std::unexpected(HostFunctionError::FieldNotFound)));
+
+    EXPECT_EQ(hostAnswer(), hfErrorToInt(HostFunctionError::FieldNotFound));
+}
+
+// The field cap bounds the status, not just the bytes: a host reporting a length past
+// `kMaxWasmDataLength` is too large whatever the guest's buffer was.
+TEST_F(CurrentLedgerObjFieldCall, FieldPastProtocolCapIsTooLarge)
+{
+    EXPECT_CALL(host, getCurrentLedgerObjField)
+        .WillOnce(Return(Bytes(kMaxWasmDataLength + 1, 0xab)));
+
+    EXPECT_EQ(hostAnswer(), hfErrorToInt(HostFunctionError::DataFieldTooLarge));
+}
+
+}  // namespace xrpl::test
diff --git a/src/tests/libxrpl/tx/wasm/host_calls/LedgerSqn.cpp b/src/tests/libxrpl/tx/wasm/host_calls/LedgerSqn.cpp
new file mode 100644
index 00000000000..d4cec43616e
--- /dev/null
+++ b/src/tests/libxrpl/tx/wasm/host_calls/LedgerSqn.cpp
@@ -0,0 +1,69 @@
+#include <xrpl/tx/wasm/WasmCommon.h>
+
+#include <gmock/gmock.h>
+#include <gtest/gtest.h>
+#include <tx/wasm/WasmFixture.h>
+
+#include <expected>
+#include <string>
+
+namespace xrpl::test {
+
+using testing::Return;
+
+// ldgr_index — no input, one scalar output.
+struct LedgerSqnCall : HostCallTest
+{
+    [[nodiscard]] std::string
+    wat() const override
+    {
+        return std::string{R"wat(
+(module
+  (import "host_lib" "ldgr_index" (func $ldgr_index (param i32 i32) (result i32)))
+  (memory (export "memory") 1)
+
+  ;; Four bytes is what the value needs. Returns what the host wrote, or its error code.
+  (func (export "escrow_finish") (result i32)
+    (local $n i32)
+    (local.set $n (call $ldgr_index (i32.const 0) (i32.const 4)))
+    (select (local.get $n) (i32.load (i32.const 0)) (i32.lt_s (local.get $n) (i32.const 0))))
+
+  ;; Two bytes is not enough for the value. Returns the host's code when memory is still
+  ;; zero, or 1 if anything was written into it - so a refused write is visibly a refusal
+  ;; and not a truncation.
+  (func (export "into_two_bytes") (result i32)
+    (local $n i32)
+    (local.set $n (call $ldgr_index (i32.const 0) (i32.const 2)))
+    (select (local.get $n) (i32.const 1) (i32.eqz (i32.load (i32.const 0))))))
+)wat"};
+    }
+};
+
+TEST_F(LedgerSqnCall, SequenceReachesGuestAsFourLittleEndianBytes)
+{
+    EXPECT_CALL(host, getLedgerSqn()).WillOnce(Return(0x01020304u));
+
+    // Read back with `i32.load`, which is little-endian by the wasm spec — so the value
+    // arriving intact is the byte order being right.
+    EXPECT_EQ(hostAnswer(), 0x01020304);
+}
+
+TEST_F(LedgerSqnCall, HostErrorBecomesContractReturnValue)
+{
+    EXPECT_CALL(host, getLedgerSqn())
+        .WillOnce(Return(std::unexpected(HostFunctionError::LedgerObjNotFound)));
+
+    EXPECT_EQ(hostAnswer(), hfErrorToInt(HostFunctionError::LedgerObjNotFound));
+}
+
+// The engine decides the fit, not the host: the host is never told the guest's capacity, it
+// reports the value's true length and the engine turns a length past the buffer into
+// `BufferTooSmall` — with nothing written.
+TEST_F(LedgerSqnCall, BufferTooSmallIsRefusedWholeNotTruncated)
+{
+    EXPECT_CALL(host, getLedgerSqn()).WillOnce(Return(0x01020304u));
+
+    EXPECT_EQ(hostAnswer("into_two_bytes"), hfErrorToInt(HostFunctionError::BufferTooSmall));
+}
+
+}  // namespace xrpl::test
diff --git a/src/tests/libxrpl/tx/wasm/host_calls/Sha512Half.cpp b/src/tests/libxrpl/tx/wasm/host_calls/Sha512Half.cpp
new file mode 100644
index 00000000000..3653a6e9313
--- /dev/null
+++ b/src/tests/libxrpl/tx/wasm/host_calls/Sha512Half.cpp
@@ -0,0 +1,78 @@
+#include <xrpl/tx/wasm/WasmCommon.h>
+
+#include <gmock/gmock.h>
+#include <gtest/gtest.h>
+#include <tx/wasm/MockHostFunctions.h>
+#include <tx/wasm/WasmFixture.h>
+
+#include <expected>
+#include <string>
+
+namespace xrpl::test {
+
+using testing::Return;
+
+// sha512_half — bytes in and bytes out, the shape that needs the engine's output buffer.
+struct Sha512HalfCall : HostCallTest
+{
+    [[nodiscard]] std::string
+    wat() const override
+    {
+        return std::string{R"wat(
+(module
+  (import "host_lib" "sha512_half" (func $sha512_half (param i32 i32 i32 i32) (result i32)))
+  (memory (export "memory") 1)
+  (data (i32.const 64) "abc")
+
+  ;; Hashes the three bytes at 64 into the 32 at 0, then returns the first four bytes of the
+  ;; digest so the answer is shown to have arrived, not just been counted.
+  (func (export "escrow_finish") (result i32)
+    (local $n i32)
+    (local.set $n (call $sha512_half (i32.const 64) (i32.const 3) (i32.const 0) (i32.const 32)))
+    (select (local.get $n) (i32.load (i32.const 0)) (i32.lt_s (local.get $n) (i32.const 0))))
+
+  ;; Reports the length the host gave, for the cases where the digest itself is not the point.
+  (func (export "digest_length") (result i32)
+    (call $sha512_half (i32.const 64) (i32.const 3) (i32.const 0) (i32.const 32))))
+)wat"};
+    }
+
+    // A digest whose first four bytes are distinctive, so the load below cannot pass by
+    // accident.
+    static Hash
+    digest()
+    {
+        Hash value;
+        value.begin()[0] = 0x0d;
+        value.begin()[1] = 0x0c;
+        value.begin()[2] = 0x0b;
+        value.begin()[3] = 0x0a;
+        return value;
+    }
+};
+
+// Both directions in one call: the guest's bytes reach the host borrowed from its memory, and
+// the answer comes back into the same memory through the engine's buffer.
+TEST_F(Sha512HalfCall, GuestBytesReachHostAndDigestComesBack)
+{
+    EXPECT_CALL(host, computeSha512HalfHash(BytesAre("abc"))).WillOnce(Return(digest()));
+
+    EXPECT_EQ(hostAnswer(), 0x0a0b0c0d) << "the digest's first four bytes, little-endian";
+}
+
+TEST_F(Sha512HalfCall, DigestIsThirtyTwoBytes)
+{
+    EXPECT_CALL(host, computeSha512HalfHash).WillOnce(Return(digest()));
+
+    EXPECT_EQ(hostAnswer("digest_length"), 32);
+}
+
+TEST_F(Sha512HalfCall, HostErrorBecomesContractReturnValue)
+{
+    EXPECT_CALL(host, computeSha512HalfHash)
+        .WillOnce(Return(std::unexpected(HostFunctionError::InvalidParams)));
+
+    EXPECT_EQ(hostAnswer(), hfErrorToInt(HostFunctionError::InvalidParams));
+}
+
+}  // namespace xrpl::test
diff --git a/src/tests/libxrpl/tx/wasm/host_calls/Trace.cpp b/src/tests/libxrpl/tx/wasm/host_calls/Trace.cpp
new file mode 100644
index 00000000000..5ed645ae2b4
--- /dev/null
+++ b/src/tests/libxrpl/tx/wasm/host_calls/Trace.cpp
@@ -0,0 +1,220 @@
+#include <xrpl/basics/Number.h>
+#include <xrpl/protocol/AccountID.h>
+#include <xrpl/protocol/Protocol.h>
+#include <xrpl/protocol/STAmount.h>
+#include <xrpl/protocol/Serializer.h>
+#include <xrpl/tx/wasm/HostFunc.h>
+#include <xrpl/tx/wasm/WasmCommon.h>
+
+#include <gmock/gmock.h>
+#include <gtest/gtest.h>
+#include <tx/wasm/MockHostFunctions.h>
+#include <tx/wasm/WasmFixture.h>
+// For `TraceDataType`, which the bridge declares and this header defines.
+#include <xrpl_wasm_vm_ffi_cxxbridge/lib.h>
+
+#include <cstdint>
+#include <format>
+#include <string>
+#include <string_view>
+#include <utility>
+
+namespace xrpl::test {
+
+namespace {
+
+// Bytes as a WAT data segment's contents. Hex-escaped throughout, so a buffer needs no
+// thought about which of its bytes the text format would otherwise read.
+std::string
+watBytes(Bytes const& bytes)
+{
+    std::string escaped;
+    escaped.reserve(bytes.size() * 4);
+    for (auto const byte : bytes)
+        escaped += std::format("\\{:02x}", byte);
+    return escaped;
+}
+
+Bytes
+serialized(STAmount const& amount)
+{
+    Serializer s;
+    amount.add(s);
+    return s.getData();
+}
+
+}  // namespace
+
+// trace — a message, a data type, and a buffer holding what that type says. One import for
+// what were five, so what a test varies is the type rather than the function.
+//
+// The buffer arrives as bytes and leaves as text: `HostContext` renders it, and the host is
+// handed the finished line. So a test says which renderer the type selected.
+struct TraceCall : HostCallTest
+{
+    static constexpr std::int32_t kDataAt = 64;
+
+    // What the guest passes. `typeCode` rather than a `TraceDataType` so a test can send a
+    // code that names no type, which is the guest's to get wrong.
+    std::int32_t typeCode{static_cast<std::int32_t>(TraceDataType::AsText)};
+    Bytes data;
+
+    void
+    traces(TraceDataType type, Bytes bytes)
+    {
+        typeCode = static_cast<std::int32_t>(type);
+        data = std::move(bytes);
+    }
+
+    void
+    traces(TraceDataType type, std::string_view text)
+    {
+        traces(type, Bytes{text.begin(), text.end()});
+    }
+
+    [[nodiscard]] std::string
+    wat() const override
+    {
+        // {0} data offset, {1} the data itself, {2} the type under test, {3} its length,
+        // {4} a type the constant modules can name, {5} the data cap.
+        return std::format(
+            R"wat(
+(module
+  (import "host_lib" "trace" (func $trace (param i32 i32 i32 i32 i32)))
+  (memory (export "memory") 1)
+  (data (i32.const 0) "note")
+  (data (i32.const {0}) "{1}")
+
+  (func (export "escrow_finish") (result i32)
+    (call $trace (i32.const 0) (i32.const 4) (i32.const {2}) (i32.const {0}) (i32.const {3}))
+    (i32.const 1))
+
+  (func (export "unnamed_type") (result i32)
+    (call $trace (i32.const 0) (i32.const 4) (i32.const 0) (i32.const {0}) (i32.const 0))
+    (i32.const 1))
+
+  (func (export "past_memory") (result i32)
+    (call $trace (i32.const 0) (i32.const 4) (i32.const {4}) (i32.const 65536) (i32.const 1))
+    (i32.const 1))
+
+  (func (export "too_long") (result i32)
+    (call $trace (i32.const 0) (i32.const 4) (i32.const {4}) (i32.const {0}) (i32.const {5}))
+    (i32.const 1)))
+)wat",
+            kDataAt,
+            watBytes(data),
+            typeCode,
+            data.size(),
+            static_cast<std::int32_t>(TraceDataType::AsHex),
+            kMaxWasmDataLength);
+    }
+
+    // The line the host was handed, for a run that is expected to reach it.
+    void
+    expectTraced(std::string_view text)
+    {
+        EXPECT_CALL(host, trace(std::string_view("note"), text));
+
+        EXPECT_EQ(hostAnswer(), 1) << "the contract runs on past its trace";
+    }
+};
+
+// The eight-byte types are the pair worth naming: the same bytes, and the type is the whole
+// difference between the two readings.
+TEST_F(TraceCall, Int64ReadsTheBufferSigned)
+{
+    traces(TraceDataType::Int64, Bytes(8, 0xff));
+
+    expectTraced("-1");
+}
+
+TEST_F(TraceCall, Uint64ReadsTheSameBufferUnsigned)
+{
+    traces(TraceDataType::Uint64, Bytes(8, 0xff));
+
+    expectTraced("18446744073709551615");
+}
+
+TEST_F(TraceCall, AsTextTakesTheBufferVerbatim)
+{
+    traces(TraceDataType::AsText, "hello");
+
+    expectTraced("hello");
+}
+
+TEST_F(TraceCall, AsHexEncodesTheBuffer)
+{
+    traces(TraceDataType::AsHex, Bytes{0x07, 0x08, 0xff});
+
+    expectTraced("0708FF");
+}
+
+// The zero account, so the expectation is the well-known base58 rather than a rendering of
+// whatever the renderer happened to do.
+TEST_F(TraceCall, AccountIsBase58)
+{
+    traces(TraceDataType::Account, Bytes(AccountID::size(), 0));
+
+    expectTraced("rrrrrrrrrrrrrrrrrrrrrhoLvTp");
+}
+
+TEST_F(TraceCall, AmountCarriesItsAssetIntoTheText)
+{
+    traces(TraceDataType::Amount, serialized(STAmount{XRPAmount{1000}}));
+
+    expectTraced("1000/XRP");
+}
+
+TEST_F(TraceCall, XfloatIsDecodedToItsValue)
+{
+    auto const encoded = wasm_float::floatFromIntImpl(
+        42, static_cast<std::int32_t>(Number::RoundingMode::ToNearest));
+    ASSERT_TRUE(encoded.has_value());
+    traces(TraceDataType::Xfloat, *encoded);
+
+    expectTraced("42");
+}
+
+// The width is part of the type, and a buffer that is not it holds no value to print. The
+// contract is not told: a trace answers nothing at all.
+TEST_F(TraceCall, ABufferOfTheWrongWidthIsDropped)
+{
+    traces(TraceDataType::Int64, Bytes(4, 0xff));
+
+    EXPECT_CALL(host, trace).Times(0);
+    EXPECT_EQ(hostAnswer(), 1);
+}
+
+// `STAmount`'s deserializer rejects this by throwing, which must not escape into the run.
+TEST_F(TraceCall, AMalformedAmountIsDroppedRatherThanThrown)
+{
+    traces(TraceDataType::Amount, Bytes(3, 0xff));
+
+    EXPECT_CALL(host, trace).Times(0);
+    EXPECT_EQ(hostAnswer(), 1);
+}
+
+// Zero is the code a guest sends by omission, which is why no type carries it.
+TEST_F(TraceCall, ACodeThatNamesNoTypeIsDropped)
+{
+    EXPECT_CALL(host, trace).Times(0);
+
+    EXPECT_EQ(hostAnswer("unnamed_type"), 1);
+}
+
+// The memory policy every input region is held to, on the one call that cannot report it.
+TEST_F(TraceCall, ARegionPastMemoryIsDropped)
+{
+    EXPECT_CALL(host, trace).Times(0);
+
+    EXPECT_EQ(hostAnswer("past_memory"), 1);
+}
+
+TEST_F(TraceCall, AMessageAndBufferPastTheDataCapAreDropped)
+{
+    EXPECT_CALL(host, trace).Times(0);
+
+    EXPECT_EQ(hostAnswer("too_long"), 1);
+}
+
+}  // namespace xrpl::test