fxrs

fxrs is a compact Rust rewrite of vercel-labs/fx. It preserves the coding-agent semantics reachable through ACP while keeping providers, authentication, tools, persistence, and host effects behind independent boundaries.

ACP over stdio is the only supported product interface. There is no TUI, standalone ask command, JavaScript SDK, WASM, or N-API surface.

Install

Install the complete command set from crates.io:

cargo install fxrs --locked

Prebuilt archives are also available from GitHub Releases. Both methods install the same three executables, which must remain in the same directory:

fxrs
fx-acp
fx-terminal-host

The latter two are private companions. fx-terminal-host retains PTYs and monitors; it is not a TUI.

To build from source:

git clone https://github.com/Leeeon233/fx-rs.git
cd fx-rs
cargo build --release --locked --workspace
./target/release/fxrs acp --help

Configure an ACP client to launch fxrs with acp as its first argument. An optional model route can be selected explicitly:

fxrs acp --model codex/gpt-5.6-sol

Authentication

The ACP initialize response advertises the codex:chatgpt authentication method. An ACP client can invoke authenticate to open the browser-based ChatGPT OAuth flow. fxrs stores credentials it owns under ~/.fx/credentials, with private permissions, process locks, and atomic replacement.

If no fxrs-owned credential exists, the Codex Provider can read a valid ~/.codex/auth.json created by codex login. That ambient credential is never refreshed, rewritten, or deleted by fxrs.

Architecture

Codex is the first concrete Provider. The registry supports multiple providers at once and routes models as provider/model, so adding OpenAI API-key, Anthropic, or other adapters does not change the agent loop, ACP projection, credential store, or child-agent model selection.

ACP-reachable capabilities include durable event-log sessions, streaming and cancellation, permission review, filesystem tools, PTY sessions and monitors, web search/fetch, skills, memory, stored tool results, MCP stdio/Streamable HTTP tools, scoped project instructions, and durable subagents.

See the architecture, migration map, release procedure, and frozen Zig source inventory.

Development

cargo fmt --all --check
cargo clippy --workspace --all-targets --locked -- -D warnings
cargo test --workspace --locked

See the contribution guidelines and security policy.

License