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.

It includes a fast full-screen terminal interface and an ACP stdio server. The TUI is itself an ACP client, so interactive use and editor integrations share the same provider, authentication, session, tool, and permission semantics.

Quick start

Start the terminal interface in the current workspace:

fxrs

Enter sends a prompt, Shift+Enter inserts a newline, Esc cancels an active turn, Ctrl+M selects a model, and Shift+Tab cycles the session mode. Use /help for the complete keyboard and command reference. Notable commands include /login, /model, /mode, /resume, /new, /clear, and /quit. Typing / opens a filtered command list; use Up/Down to select, Tab to complete, Enter to run, and Esc to close it.

The interface streams Markdown responses and reasoning, updates tool cards in place, provides foldable scrollback, queues follow-up prompts, and presents ACP permission requests as keyboard- and mouse-operable cards. Set NO_COLOR=1 for a monochrome theme.

The focus, scrollback, and contextual-permission interactions take inspiration from xAI's grok-build; fxrs keeps its implementation and runtime architecture independent.

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 four executables, which must remain in the same directory:

fxrs
fx-tui
fx-acp
fx-terminal-host

fx-tui is the interactive frontend. fx-acp and fx-terminal-host are private companions; the latter retains PTYs and monitors across sessions.

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

Resume a durable session or select a different workspace with:

fxrs tui --session <session-id>
fxrs tui --cwd /path/to/project

ACP integration

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
fxrs acp --model vercel/zai/glm-5.2

Authentication

The ACP initialize response advertises both codex:chatgpt and vercel:oauth. An ACP client can invoke authenticate to start the provider-owned browser flow. Vercel uses OIDC discovery and device authorization; the verification URL and code are also written to stderr in case a browser cannot be opened. fxrs stores credentials it owns under ~/.fx/credentials, with private permissions, process locks, refresh-token rotation, 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.

Vercel AI Gateway also accepts ambient credentials without persisting them. Resolution order is VERCEL_OIDC_TOKEN, AI_GATEWAY_API_KEY, then the fxrs-owned Vercel OAuth session. Set FX_VERCEL_TEAM to a team ID (or a slug during OAuth login); otherwise OAuth selects the first team returned by Vercel. FX_VERCEL_MODELS can add comma-separated Gateway model IDs to the built-in cold-start catalog without performing network I/O during ACP initialization.

In the TUI, run /login to invoke the advertised authentication method; when multiple providers advertise methods, fxrs opens a provider picker. Authentication remains provider-owned, and the frontend contains no Codex-specific credential logic.

Architecture

Codex and Vercel AI Gateway are loaded simultaneously. The registry routes models as provider/model; Vercel's provider-local IDs retain their own vendor prefix, for example vercel/anthropic/claude-sonnet-4.6. Adding another provider 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

Licensed under the Apache License 2.0.