Josh McKinney
e416e578bb
## Problem The first user turn can pay websocket handshake latency even when a session has already started. We want to reduce that initial delay while preserving turn semantics and avoiding any prompt send during startup. Reviewer feedback also called out duplicated connect/setup paths and unnecessary preconnect state complexity. ## Mental model `ModelClient` owns session-scoped transport state. During session startup, it can opportunistically warm one websocket handshake slot. A turn-scoped `ModelClientSession` adopts that slot once if available, restores captured sticky turn-state, and otherwise opens a websocket through the same shared connect path. If startup preconnect is still in flight, first turn setup awaits that task and treats it as the first connection attempt for the turn. Preconnect is handshake-only. The first `response.create` is still sent only when a turn starts. ## Non-goals This change does not make preconnect required for correctness and does not change prompt/turn payload semantics. It also does not expand fallback behavior beyond clearing preconnect state when fallback activates. ## Tradeoffs The implementation prioritizes simpler ownership and shared connection code over header-match gating for reuse. The single-slot cache keeps lifecycle straightforward but only benefits the immediate next turn. Awaiting in-flight preconnect has the same app-level connect-timeout semantics as existing websocket connect behavior (no new timeout class introduced by this PR). ## Architecture `core/src/client.rs`: - Added session-level preconnect lifecycle state (`Idle` / `InFlight` / `Ready`) carrying one warmed websocket plus optional captured turn-state. - Added `pre_establish_connection()` startup warmup and `preconnect()` handshake-only setup. - Deduped auth/provider resolution into `current_client_setup()` and websocket handshake wiring into `connect_websocket()` / `build_websocket_headers()`. - Updated turn websocket path to adopt preconnect first, await in-flight preconnect when present, then create a new websocket only when needed. - Ensured fallback activation clears warmed preconnect state. - Added documentation for lifecycle, ownership, sticky-routing invariants, and timeout semantics. `core/src/codex.rs`: - Session startup invokes `model_client.pre_establish_connection(...)`. - Turn metadata resolution uses the shared timeout helper. `core/src/turn_metadata.rs`: - Centralized shared timeout helper used by both turn-time metadata resolution and startup preconnect metadata building. `core/tests/common/responses.rs` + websocket test suites: - Added deterministic handshake waiting helper (`wait_for_handshakes`) with bounded polling. - Added startup preconnect and in-flight preconnect reuse coverage. - Fallback expectations now assert exactly two websocket attempts in covered scenarios (startup preconnect + turn attempt before fallback sticks). ## Observability Preconnect remains best-effort and non-fatal. Existing websocket/fallback telemetry remains in place, and debug logs now make preconnect-await behavior and preconnect failures easier to reason about. ## Tests Validated with: 1. `just fmt` 2. `cargo test -p codex-core websocket_preconnect -- --nocapture` 3. `cargo test -p codex-core websocket_fallback -- --nocapture` 4. `cargo test -p codex-core websocket_first_turn_waits_for_inflight_preconnect -- --nocapture`
Codex CLI (Rust Implementation)
We provide Codex CLI as a standalone, native executable to ensure a zero-dependency install.
Installing Codex
Today, the easiest way to install Codex is via npm:
npm i -g @openai/codex
codex
You can also install via Homebrew (brew install --cask codex) or download a platform-specific release directly from our GitHub Releases.
Documentation quickstart
- First run with Codex? Start with
docs/getting-started.md(links to the walkthrough for prompts, keyboard shortcuts, and session management). - Want deeper control? See
docs/config.mdanddocs/install.md.
What's new in the Rust CLI
The Rust implementation is now the maintained Codex CLI and serves as the default experience. It includes a number of features that the legacy TypeScript CLI never supported.
Config
Codex supports a rich set of configuration options. Note that the Rust CLI uses config.toml instead of config.json. See docs/config.md for details.
Model Context Protocol Support
MCP client
Codex CLI functions as an MCP client that allows the Codex CLI and IDE extension to connect to MCP servers on startup. See the configuration documentation for details.
MCP server (experimental)
Codex can be launched as an MCP server by running codex mcp-server. This allows other MCP clients to use Codex as a tool for another agent.
Use the @modelcontextprotocol/inspector to try it out:
npx @modelcontextprotocol/inspector codex mcp-server
Use codex mcp to add/list/get/remove MCP server launchers defined in config.toml, and codex mcp-server to run the MCP server directly.
Notifications
You can enable notifications by configuring a script that is run whenever the agent finishes a turn. The notify documentation includes a detailed example that explains how to get desktop notifications via terminal-notifier on macOS. When Codex detects that it is running under WSL 2 inside Windows Terminal (WT_SESSION is set), the TUI automatically falls back to native Windows toast notifications so approval prompts and completed turns surface even though Windows Terminal does not implement OSC 9.
codex exec to run Codex programmatically/non-interactively
To run Codex non-interactively, run codex exec PROMPT (you can also pass the prompt via stdin) and Codex will work on your task until it decides that it is done and exits. Output is printed to the terminal directly. You can set the RUST_LOG environment variable to see more about what's going on.
Use codex exec --ephemeral ... to run without persisting session rollout files to disk.
Experimenting with the Codex Sandbox
To test to see what happens when a command is run under the sandbox provided by Codex, we provide the following subcommands in Codex CLI:
# macOS
codex sandbox macos [--full-auto] [--log-denials] [COMMAND]...
# Linux
codex sandbox linux [--full-auto] [COMMAND]...
# Windows
codex sandbox windows [--full-auto] [COMMAND]...
# Legacy aliases
codex debug seatbelt [--full-auto] [--log-denials] [COMMAND]...
codex debug landlock [--full-auto] [COMMAND]...
Selecting a sandbox policy via --sandbox
The Rust CLI exposes a dedicated --sandbox (-s) flag that lets you pick the sandbox policy without having to reach for the generic -c/--config option:
# Run Codex with the default, read-only sandbox
codex --sandbox read-only
# Allow the agent to write within the current workspace while still blocking network access
codex --sandbox workspace-write
# Danger! Disable sandboxing entirely (only do this if you are already running in a container or other isolated env)
codex --sandbox danger-full-access
The same setting can be persisted in ~/.codex/config.toml via the top-level sandbox_mode = "MODE" key, e.g. sandbox_mode = "workspace-write".
Code Organization
This folder is the root of a Cargo workspace. It contains quite a bit of experimental code, but here are the key crates:
core/contains the business logic for Codex. Ultimately, we hope this to be a library crate that is generally useful for building other Rust/native applications that use Codex.exec/"headless" CLI for use in automation.tui/CLI that launches a fullscreen TUI built with Ratatui.cli/CLI multitool that provides the aforementioned CLIs via subcommands.