rs-bun

Use this agent for any task connecting Rust and Bun: writing or debugging a bun:ffi binding, building a napi-rs native addon, deciding between FFI / N-API / subprocess / WASM, packaging a Rust crate as a Bun package, generating the TypeScript bindings for a cdylib, or chasing an FFI crash (segfault, garbage value, memory corruption) from Bun into native Rust. Triggers include "call my Rust from Bun", "bind this crate to Bun", "should I use FFI or N-API", "ship Rust as a Bun/npm package", "my bun:ffi call crashes", or building a Rust↔JS native module. It owns the build/test loop (cargo + bun test) and proves the round trip rather than guessing.

Build a complete, correct Rust↔Bun FFI bridge for ANY Rust project: a `cdylib` crate exposing `extern "C"` functions that Bun loads with `bun:ffi` (`dlopen`/`cc`/`JSCallback`). Use this skill whenever the user wants to call Rust from Bun/JavaScript, "bind a Rust crate to Bun", "expose Rust to bun:ffi", pass strings/structs/buffers/callbacks across the Rust↔JS boundary, generate the TypeScript `dlopen` bindings for a native library, or debug FFI crashes (segfaults, wrong values, memory corruption) when using bun:ffi — even if they just say "I want my Rust function callable from Bun" without naming FFI.

Build production Rust native addons (`.node`) with napi-rs (v3) for Bun and Node: the `#[napi]` macro surface (functions, objects, classes, getters, async), errors-as-thrown-exceptions, Buffer/typed-array values, ThreadsafeFunction for cross-thread callbacks, the `@napi-rs/cli` build, and the multi-platform prebuild/publish model. Use this skill whenever the user wants a Rust native module for Bun/Node that needs rich JS values, async, classes, or thrown errors, says "use napi-rs", "build a .node addon in Rust", "Rust addon for Bun", wants the stable/production alternative to bun:ffi, needs to cross-compile and publish a native package, or is debugging a napi-rs build or a napi addon under Bun — even if they just say "make my Rust into a fast Node/Bun module".

Turn a Rust crate into a usable, distributable Bun package via bun:ffi — project layout, automated build (cargo → cdylib → typed TS bindings), a fast prototyping loop, and multi-platform distribution (prebuilt per-platform deps, build-from-source, or embedding the library with `bun build --compile`). Use this skill whenever the user wants to "package a Rust crate for Bun", "ship Rust as an npm/Bun package", "wrap my Rust library so JS can import it", set up the build/automation/CI for a Rust+Bun project, generate TypeScript bindings from a symbol manifest, prototype a Rust↔Bun binding quickly, or distribute a native Bun package across platforms — even if they only say "make my Rust crate installable from Bun".

The reference and decision guide for connecting Rust and Bun in ANY project: every integration path (bun:ffi cdylib, N-API via napi-rs, Bun.spawn subprocess, WebAssembly, stdio IPC), how to choose between them, the complete cross-boundary type-marshalling rules, and how Bun itself bridges Rust↔JS internally (the canonical reference patterns from the official oven-sh/bun repo: the FFI JIT trampoline, bun_jsc/host_fn, the .classes.ts codegen, bun_sys/bun_core). Use this skill whenever the user asks "how do Rust and Bun fit together", "what's the best way to call Rust from Bun", "should I use FFI or N-API", needs the Rust↔JS type mapping, is architecting a native module for Bun, or wants to understand how Bun's own Rust internals talk to JavaScript — even if they don't name a specific mechanism.

Build and run Rust→WebAssembly modules from Bun with wasm-bindgen: the setup, the `#[wasm_bindgen]` macro surface (functions, classes, Result→throw, async, importing JS, js-sys), the `wasm-pack` build, and — critically — which target actually loads under Bun (`nodejs`, NOT `bundler`). Use this skill whenever the user wants to call Rust from Bun via WASM, "use wasm-bindgen", "wasm-pack with Bun", run a `.wasm` from a Rust crate in Bun, wants a portable sandboxed Rust artifact instead of a native addon, or is debugging why a wasm-bindgen module won't load in Bun (`__wbindgen_start is not a function`, wasm import resolving to a string) — even if they just say "compile my Rust to WASM for Bun".