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# Preserve PATH precedence & fix Windows MCP env propagation ## Problem & intent Preserve user PATH precedence and reduce Windows setup friction for MCP servers by avoiding PATH reordering and ensuring Windows child processes receive essential env vars. - Addresses: #4180 #5225 #2945 #3245 #3385 #2892 #3310 #3457 #4370 - Supersedes: #4182, #3866, #3828 (overlapping/inferior once this merges) - Notes: #2626 / #2646 are the original PATH-mutation sources being corrected. --- ## Before / After **Before** - PATH was **prepended** with an `apply_patch` helper dir (Rust + Node wrapper), reordering tools and breaking virtualenvs/shims on macOS/Linux. - On Windows, MCP servers missed core env vars and often failed to start without explicit per-server env blocks. **After** - Helper dir is **appended** to PATH (preserves user/tool precedence). - Windows MCP child env now includes common core variables and mirrors `PATH` → `Path`, so typical CLIs/plugins work **without** per-server env blocks. --- ## Scope of change ### `codex-rs/arg0/src/lib.rs` - Append temp/helper dir to `PATH` instead of prepending. ### `codex-cli/bin/codex.js` - Mirror the same append behavior for the Node wrapper. ### `codex-rs/rmcp-client/src/utils.rs` - Expand Windows `DEFAULT_ENV_VARS` (e.g., `COMSPEC`, `SYSTEMROOT`, `PROGRAMFILES*`, `APPDATA`, etc.). - Mirror `PATH` → `Path` for Windows child processes. - Small unit test; conditional `mut` + `clippy` cleanup. --- ## Security effects No broadened privileges. Only environment propagation for well-known Windows keys on stdio MCP child processes. No sandbox policy changes and no network additions. --- ## Testing evidence **Static** - `cargo fmt` - `cargo clippy -p codex-arg0 -D warnings` → **clean** - `cargo clippy -p codex-rmcp-client -D warnings` → **clean** - `cargo test -p codex-rmcp-client` → **13 passed** **Manual** - Local verification on Windows PowerShell 5/7 and WSL (no `unused_mut` warnings on non-Windows targets). --- ## Checklist - [x] Append (not prepend) helper dir to PATH in Rust and Node wrappers - [x] Windows MCP child inherits core env vars; `PATH` mirrored to `Path` - [x] `cargo fmt` / `clippy` clean across touched crates - [x] Unit tests updated/passing where applicable - [x] Cross-platform behavior preserved (macOS/Linux PATH precedence intact)
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? Follow the walkthrough in
docs/getting-started.mdfor prompts, keyboard shortcuts, and session management. - Already shipping with Codex and want deeper control? Jump to
docs/advanced.mdand the configuration reference atdocs/config.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.
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.
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] [COMMAND]...
# Linux
codex sandbox linux [--full-auto] [COMMAND]...
# Legacy aliases
codex debug seatbelt [--full-auto] [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.