diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 99e0ab9..45dac46 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -93,6 +93,13 @@ jobs:
       - name: Build the wasm package
         run: bun run build
 
+      # `bun run build` regenerates the type file. If what it produced differs
+      # from what is committed, the tarball's .d.ts would not be the reviewed
+      # one — which is how a build with missing sources shipped a .d.ts
+      # referencing types it no longer declared.
+      - name: Fail if the generated types drifted
+        run: git diff --exit-code -- src/generated_types.rs
+
       - name: Run Tests with Bun
         run: bun test
         env:
diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index fb97b9f..fcc738b 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -243,6 +243,13 @@ jobs:
       - name: Build the wasm package
         run: bun run build
 
+      # `bun run build` regenerates the type file. If what it produced differs
+      # from what is committed, the tarball's .d.ts would not be the reviewed
+      # one — which is how a build with missing sources shipped a .d.ts
+      # referencing types it no longer declared.
+      - name: Fail if the generated types drifted
+        run: git diff --exit-code -- src/generated_types.rs
+
       - run: bun test
 
       - name: Rust unit tests (wasm32 in Node)
@@ -322,6 +329,12 @@ jobs:
       - name: Build the wasm package
         run: bun run build
 
+      # The tarball is built from this step's output, so the same drift
+      # check applies here: publish what was reviewed, not what a runner
+      # happened to regenerate.
+      - name: Fail if the generated types drifted
+        run: git diff --exit-code -- src/generated_types.rs
+
       # `--ignore-scripts` below suppresses the prepack hook, and prepack is
       # where the tarball guard lives — run it directly so a build that leaks
       # pkg/ or duplicate files still fails before publishing.
diff --git a/codegen/src/main.rs b/codegen/src/main.rs
index b54e878..373ce11 100644
--- a/codegen/src/main.rs
+++ b/codegen/src/main.rs
@@ -12,6 +12,14 @@ use walkdir::WalkDir;
 
 /// Find whatsapp-rust source dir from Cargo's git cache by parsing Cargo.lock.
 /// Falls back to `../../whatsapp-rust/` for local development.
+///
+/// This crate does not depend on whatsapp-rust, so `cargo run` never fetches
+/// it: the sources have to already be on disk. On a machine where they are not
+/// — a CI runner with a cold cache, where `gen` runs before anything downloads
+/// the core — every lookup below misses, and `WalkDir` over a missing directory
+/// yields nothing rather than erroring. That silently produced a type file with
+/// almost everything missing, which still compiled and shipped a `.d.ts`
+/// referencing types it no longer declared. Hence `require_sources`.
 fn find_whatsapp_rust_root() -> PathBuf {
     // Try to find it in Cargo's git checkout cache
     let lock_path = Path::new("../Cargo.lock");
@@ -55,8 +63,39 @@ fn find_whatsapp_rust_root() -> PathBuf {
     fallback
 }
 
+/// Refuse to generate from sources that are not there. Parsing nothing is not
+/// an empty result, it is a broken one.
+///
+/// Every path the generator reads is checked, not just the first: `wacore`
+/// alone contributes enough types that a checkout missing only `src/` would
+/// produce a plausible-looking file and slip past an emptiness check.
+fn require_sources(root: &Path) {
+    let missing: Vec<String> = REQUIRED_SOURCES
+        .iter()
+        .map(|rel| root.join(rel))
+        .filter(|path| !path.exists())
+        .map(|path| path.display().to_string())
+        .collect();
+
+    assert!(
+        missing.is_empty(),
+        "whatsapp-rust sources are incomplete at {}\n\
+         Missing: {}\n\
+         This generator reads the core's sources off disk rather than depending on it, so \n\
+         `cargo fetch` has to have populated the git checkout — that is what `gen:bridge-types` \n\
+         runs first. A sibling clone of whatsapp-rust also works.",
+        root.display(),
+        missing.join(", ")
+    );
+}
+
+/// Everything `main` parses. Kept next to the guard so adding a source without
+/// guarding it is a visible omission rather than a silent one.
+const REQUIRED_SOURCES: [&str; 4] = ["wacore/src", "src/features", "src/types", "src/send"];
+
 fn main() {
     let root = find_whatsapp_rust_root();
+    require_sources(&root);
     let wacore_dir = root.join("wacore/src");
     let src_dir = root.join("src");
 
@@ -71,8 +110,12 @@ fn main() {
         parse_file(entry.path(), &mut all_types);
     }
 
-    // Parse whatsapp-rust feature types
-    let feature_dirs = ["features", "types"];
+    // Parse whatsapp-rust feature types. `send` replaces a hardcoded read of
+    // `send.rs`, which the core has since split into a module: the old path
+    // stopped matching and the call did nothing. Nothing was lost — the types
+    // it named are not `Serialize`, so this generator never emitted them — but
+    // pointing at what exists keeps the guard above honest.
+    let feature_dirs = ["features", "types", "send"];
     for dir in feature_dirs {
         let path = src_dir.join(dir);
         if path.exists() {
@@ -89,6 +132,18 @@ fn main() {
     // Also parse send.rs for SendOptions/RevokeType
     parse_file(&src_dir.join("send.rs"), &mut all_types);
 
+    // Reported so a collapse is visible in the build log. Deliberately not
+    // asserted against a floor: the real count is what it is, and a threshold
+    // close to it breaks every legitimate change to the core. What guards the
+    // output is `require_sources` above and the drift check in CI, which
+    // compares against the committed file instead of guessing a number.
+    eprintln!("parsed {} types from {}", all_types.len(), root.display());
+    assert!(
+        !all_types.is_empty(),
+        "no types parsed from {}: refusing to generate an empty type file",
+        root.display()
+    );
+
     // Build TypeScript content
     let mut ts = String::new();
 
diff --git a/package.json b/package.json
index f472aaf..b6b740c 100644
--- a/package.json
+++ b/package.json
@@ -30,7 +30,7 @@
     "scripts": {
         "bench": "bun run build && bun run benches/binary.ts && bun run benches/signal.ts && bun run benches/curve.ts && bun run benches/crypto.ts",
         "bench:node": "bun run build && node --expose-gc benches/binary.ts && node --expose-gc benches/signal.ts && node --expose-gc benches/curve.ts && node --expose-gc benches/crypto.ts",
-        "gen:bridge-types": "cd codegen && cargo run -q --bin gen-types --target $(rustc -vV | grep host | cut -d' ' -f2) > ../src/generated_types.rs.tmp && mv ../src/generated_types.rs.tmp ../src/generated_types.rs",
+        "gen:bridge-types": "cargo fetch && cd codegen && cargo run -q --bin gen-types --target $(rustc -vV | grep host | cut -d' ' -f2) > ../src/generated_types.rs.tmp && mv ../src/generated_types.rs.tmp ../src/generated_types.rs",
         "gen:proto-codec": "bun run scripts/gen-ts-proto.ts",
         "gen:proto-types": "bun run scripts/gen-protobufjs-dts.ts",
         "gen": "bun run gen:bridge-types && bun run gen:proto-codec && bun run gen:proto-types",