gate4agent

Universal Rust transport library for CLI AI agents. Spawn, stream, resume — for four different CLI agents through one unified API.

Not a harness. Not a sandbox. gate4agent is the thin wiring layer between your Rust app and the CLI agent's subprocess: spawn the binary, write the prompt, read structured events, resume by session id. That's it.

Supported CLI tools

Transport classes:

• Pipe: spawn the CLI directly, read NDJSON over stdout
• PTY: spawn inside a pseudo-terminal, scrape the screen with vt100 (for agents without structured output)

Quick start

use gate4agent::{TransportSession, SpawnOptions, CliTool, AgentEvent};
use std::path::PathBuf;

#[tokio::main]
async fn main() -> anyhow::Result<()> {
    let opts = SpawnOptions {
        working_dir: PathBuf::from("."),
        prompt: "Say hello in 3 words".into(),
        resume_session_id: None,
        model: None,
        append_system_prompt: None,
        extra_args: vec![],
        env_vars: vec![],
    };

    let session = TransportSession::spawn(
        CliTool::ClaudeCode,
        &opts.working_dir.clone(),
        &opts.prompt.clone(),
        opts,
    ).await?;

    let mut rx = session.subscribe();
    while let Ok(event) = rx.recv().await {
        match event {
            AgentEvent::Text { text, .. } => print!("{text}"),
            AgentEvent::SessionEnd { .. } => break,
            _ => {}
        }
    }
    Ok(())
}

Resume an existing session

let opts = SpawnOptions {
    resume_session_id: Some("abc-123-session".into()),
    ..opts
};

Each CLI handles resume in its own way — Codex swaps exec → exec resume <id>, Claude uses --resume <id>, OpenCode uses --session <ses_XXX>. gate4agent hides the difference behind SpawnOptions::resume_session_id.

Using PipeSession directly (backwards-compatible API)

use gate4agent::{PipeSession, PipeProcessOptions, ClaudeOptions, SessionConfig, CliTool};

let config = SessionConfig {
    tool: CliTool::ClaudeCode,
    working_dir: std::env::current_dir()?,
    env_vars: vec![],
    name: None,
};
let opts = PipeProcessOptions {
    claude: ClaudeOptions { model: Some("claude-opus-4".into()), ..Default::default() },
    ..Default::default()
};
let session = PipeSession::spawn(config, "hello", opts).await?;

Features

• Single API for 4 CLIs — TransportSession::spawn(tool, cwd, prompt, options)
• Backwards-compatible PipeSession — 0.1.x consumers that used PipeSession::spawn(config, prompt, options) compile unchanged
• SessionEnd synthesis — Codex has no terminal event; gate4agent synthesizes SessionEnd { result: "exit_code=N", is_error: N != 0 } on child exit
• Transport-neutral events — AgentEvent::{Text, ToolStart, ToolResult, Thinking, TurnComplete, SessionStart, SessionEnd}
• Cross-platform — Windows (ConPTY + cmd /C argv wrapping) and Unix (POSIX PTY + bare exec)
• Rate-limit detection — pattern-based session/daily/weekly limit detection per CLI
• Zero new dependencies — gate4agent 0.2.1 removes dead fantasy transports without adding anything new

Architecture

gate4agent/
├── src/
│   ├── lib.rs           — Library root, re-exports
│   ├── core/            — AgentEvent, CliTool, SessionConfig, AgentError
│   ├── transport/       — TransportSession (thin router over PipeSession), SpawnOptions
│   ├── pipe/            — PipeSession, PipeProcess, per-CLI NDJSON parsers + command builders
│   │   └── cli/         — claude.rs, codex.rs, gemini.rs, opencode.rs
│   ├── pty/             — PtyWrapper, PtySession, VTE/screen parsers, per-CLI PTY parsers
│   │   └── cli/         — Per-CLI PTY output parsers
│   ├── history/         — Session history reader
│   └── utils.rs         — String utilities

Testing status

PTY parsers existed in 0.1.x and are structurally simple (screen scraping) — low risk of breakage. Pipe parsers for Claude, Codex, Gemini, and OpenCode are fully live-verified.

Windows spawn strategy

On Windows, CLI tools are invoked through the appropriate shell:

• npm-installed CLIs (claude, codex, gemini, opencode): cmd /C program.cmd arg1 arg2 — the .cmd batch wrapper is detected via PATH lookup
• Bash scripts (native binaries without .cmd wrapper): bash -c 'program arg1 arg2' — fallback when no .cmd wrapper exists
• Unix: direct Command::new("program") — no shell wrapping needed

Arguments are passed individually (not joined into a shell string) to avoid cmd.exe quote-mangling issues.

Prerequisites

At least one CLI agent must be installed on the host. gate4agent does not install them.

Versioning

• 0.1.x — original 3-CLI library (Claude, Codex, Gemini)
• 0.2.0 — breaking: 6 CLIs, TransportSession, AgentEvent renamed, PipeSession removed, OpenClaw fantasy transport
• 0.2.1 — cleanup: OpenClaw removed (was never functional), PipeSession restored for 0.1.x compatibility, TransportSession is now a thin router over PipeSession
• 0.2.2 — parser isolation: NdjsonParser trait extracted, per-CLI parser modules split out
• 0.2.3 — source tree restructure into core/pty/pipe layout; proper pipe builders+parsers for Codex, Gemini, Cursor, OpenCode (research-based, NOT yet tested against live CLI output)
• 0.2.4 — docs update, Codex flags fixed (--full-auto replaces removed --ask-for-approval)
• 0.2.5 — live integration tests: fixed Codex flags, OpenCode run subcommand, Gemini -p flag, Windows cmd /C quoting; all parsers verified against real CLI output
• 0.2.6 — Gemini + OpenCode live-verified; OpenCode parser rewritten from real CLI output
• 0.2.7 — Cursor removed (no native Windows support, broken headless mode, closed-source CLI). 4 CLI tools remain: Claude Code, Codex, Gemini, OpenCode.

See ROADMAP.md for what's next and DEBUGGING.md for known issues and mitigations.

Migration guide

0.2.0 → 0.2.1

• OpenClaw removed — CliTool::OpenClaw no longer exists. If you matched on it, delete that arm. OpenClaw was never functional (unverified daemon protocol, fictional acpx API surface).
• PipeSession restored — 0.1.x callers that used PipeSession::spawn(config, prompt, options) compile again. The PipeSession now includes SessionEnd synthesis (previously only in the 0.2.0 pipe_runner).
• TransportSession is now a thin wrapper over PipeSession. Its public API (spawn, subscribe, session_id, send_prompt, kill) is unchanged. Internal: no more TransportHandle enum, no dead Pty variant.
• DaemonNotRunning / DaemonProbeTimeout error variants removed — they were only reachable via OpenClaw. Remove any match arms for these.

0.1.x → 0.2.1

1. Events: AgentEvent::Pipe* → neutral names. Rename all match arms:

   • PipeText → Text
   • PipeToolStart → ToolStart
   • PipeToolResult → ToolResult
   • PipeThinking → Thinking
   • PipeTurnComplete → TurnComplete
   • PipeSessionStart → SessionStart
   • PipeSessionEnd → SessionEnd

2. PipeSession::spawn — signature unchanged: PipeSession::spawn(config, prompt, options). Compiles directly.

3. SpawnOptions: new unified struct. Fields: working_dir, prompt, resume_session_id, model, append_system_prompt, extra_args, env_vars.

4. CliTool is now non-exhaustive in effect (new variant: OpenCode). Add arms or a _ => fallback.

Support the Project

If you find this tool useful, consider supporting development:

License

MIT