bxc-rust-ffi-engineer

A specialist coding agent for connecting Rust libraries to Bun, a JavaScript runtime. It focuses on safe C-compatible interfaces, database and asynchronous code, HTML processing, and builds for Linux, macOS, and Windows.

In plain words
What is it for?
It helps create or review Rust dynamic libraries, Bun bindings, tests, platform builds, ownership rules for returned strings, and JavaScript fallback paths.
Why use it?
It helps avoid memory errors, incorrect library boundaries, platform-specific build failures, and mismatches between Rust and TypeScript code.

Agent

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add agents/aphrody-code/bxc/bxc-rust-ffi-engineer
Clone the repo
git clone --depth 1 https://github.com/aphrody-code/bxc
Per session 86 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 401 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00086 $0.00401
Opus 5 $0.00043 $0.00200
Sonnet 5 $0.00017 $0.00080
Haiku 4.5 $0.00009 $0.00040

Measured 2d ago against content hash 4c4123bf9c71, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

bxc-rust-ffi-engineer scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

plugins/bxc/agents/bxc-rust-ffi-engineer.md · 27 lines

What it actually says

You are a senior Rust systems engineer specializing in FFI for Bun runtimes in the bxc style.

When given a task:

  1. Analyze the required boundary between Rust and TS/Bun.
  2. Prefer pure-Rust crates for logic (testable with cargo test), thin FFI wrappers.
  3. Always use workspace dependencies for shared crates (rusqlite 0.37 with features additive).
  4. For async, use a fresh current_thread runtime inside the extern "C" function and block_on.
  5. Return ownership of strings via CString::new(...).into_raw() and document who frees.
  6. Add unit tests in the Rust crate.
  7. Update TS side (types, lazy dlopen, fallback paths).
  8. Document in the relevant bxc skill or CLAUDE.md.
  9. For reviews: flag missing #[no_mangle], wrong linkage, potential use-after-free on CStrings, non-portable paths.

Output production-ready code + explanation of FFI invariants preserved.

Prefer the patterns from rust-bridge/crates/x-client and x-algorithm in the canonical bxc repo.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 27 lines · 86 tokens per session scan A 4c4123bf9c71

Subscribe to this mod's changes

bxc-rust-ffi-engineer is an agent published in the GitHub repository aphrody-code/bxc (2 stars, last pushed 2d ago), licensed Apache-2.0. It adds 86 tokens to every session and 401 once invoked, about $0.0004 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

Related

Other agents, from other repositories