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Plugins & WASM Sandbox

Zegion has two plugin runtimes: Rhai scripts (lightweight, low-spec friendly) and a sandboxed WASM runtime (for untrusted or heavier plugins). Both are auto-loaded.

Rhai script plugins

Drop a .rhai file into plugins/. It must define a main(input) function and call it. The agent runs it via the plugin_run tool; you can also call it programmatically via PluginRegistry::run(name, input).

// plugins/shout.rhai
fn main(input) {
    input + "!"
}

main(input)

Included plugins (11)

plugin description
hello example / smoke test
word_count count chars, words, lines
slugify title → URL-friendly slug
reverse reverse a string
title_case capitalize each word
dedupe_lines remove duplicate lines (order-preserving)
sort_lines sort lines alphabetically
is_palindrome palindrome check
wrap hard-wrap text to 60 columns
censor mask emails / long tokens
csv_to_table CSV → aligned text table

Rhai notes (this build)

  • Variables are declared with let (reassignable); let mut is not used.
  • Build strings with s += c.to_string(); iterate with for c in s.chars().
  • split, sort, contains, to_lower, to_upper().to_string() work; pad, trim, and string ends_with are not available in this build.

MCP plugins

MCP servers run as child processes and are bridged into tools. See mcp.md.

WASM sandbox

zegion-core/src/sandbox.rs runs guest WASM modules in wasmtime with hard limits:

  • Fuel cap (CPU) — infinite loops are killed.
  • Memory cap (RAM) — guests can't exhaust the host.
  • Fresh store per call — no state leaks between invocations.

Guest ABI

Guests export three symbols and pass strings through linear memory:

(memory (export "memory") 1)
(func (export "alloc") (param i32) (result i32))      ;; allocate n bytes -> ptr
(func (export "run") (param i32 i32) (result i64))    ;; ptr,len in -> packed ptr,len out

run returns a packed i64: high 32 bits = output pointer, low 32 bits = output length.

Exposing a WASM tool

let tool = WasmTool::compile(wat_or_wasm_bytes, SandboxLimits::default())?;
let aisdk_tool = wasm_aisdk_tool("my_tool", "what it does", input_schema, Arc::new(tool));

A minimal host_log(ptr, len) host function is provided for guest-side logging.