Michael Bolin
7134220f3c
Follow-up to [#13388](https://github.com/openai/codex/pull/13388). This uses the same general fix pattern as [#12421](https://github.com/openai/codex/pull/12421), but in the `codex-core` compact/resume/fork path. ## Why `compact_resume_after_second_compaction_preserves_history` started overflowing the stack on Windows CI after `#13388`. The important part is that this was not a compaction-recursion bug. The test exercises a path with several thin `async fn` wrappers around much larger thread-spawn, resume, and fork futures. When one `async fn` awaits another inline, the outer future stores the callee future as part of its own state machine. In a long wrapper chain, that means a caller can accidentally inline a lot more state than the source code suggests. That is exactly what was happening here: - `ThreadManager` convenience methods such as `start_thread`, `resume_thread_from_rollout`, and `fork_thread` were inlining the larger spawn/resume futures beneath them. - `core_test_support::test_codex` added another wrapper layer on top of those same paths. - `compact_resume_fork` adds a few more helpers, and this particular test drives the resume/fork path multiple times. On Windows, that was enough to push both the libtest thread and Tokio worker threads over the edge. The previous 8 MiB test-thread workaround proved the failure was stack-related, but it did not address the underlying future size. ## How This Was Debugged The useful debugging pattern here was to turn the CI-only failure into a local low-stack repro. 1. First, remove the explicit large-stack harness so the test runs on the normal `#[tokio::test]` path. 2. Build the test binary normally. 3. Re-run the already-built `tests/all` binary directly with progressively smaller `RUST_MIN_STACK` values. Running the built binary directly matters: it keeps the reduced stack size focused on the test process instead of also applying it to `cargo` and `rustc`. That made it possible to answer two questions quickly: - Does the failure still reproduce without the workaround? Yes. - Does boxing the wrapper futures actually buy back stack headroom? Also yes. After this change, the built test binary passes with `RUST_MIN_STACK=917504` and still overflows at `786432`, which is enough evidence to justify removing the explicit 8 MiB override while keeping a deterministic low-stack repro for future debugging. If we hit a similar issue again, the first places to inspect are thin `async fn` wrappers that mostly forward into a much larger async implementation. ## `Box::pin()` Primer `async fn` compiles into a state machine. If a wrapper does this: ```rust async fn wrapper() { inner().await; } ``` then `wrapper()` stores the full `inner()` future inline as part of its own state. If the wrapper instead does this: ```rust async fn wrapper() { Box::pin(inner()).await; } ``` then the child future lives on the heap, and the outer future only stores a pinned pointer to it. That usually trades one allocation for a substantially smaller outer future, which is exactly the tradeoff we want when the problem is stack pressure rather than raw CPU time. Useful references: - [`Box::pin`](https://doc.rust-lang.org/std/boxed/struct.Box.html#method.pin) - [Async book: Pinning](https://rust-lang.github.io/async-book/04_pinning/01_chapter.html) ## What Changed - Boxed the wrapper futures in `core/src/thread_manager.rs` around `start_thread`, `resume_thread_from_rollout`, `fork_thread`, and the corresponding `ThreadManagerState` spawn helpers so callers no longer inline the full spawn/resume state machine through multiple layers. - Boxed the matching test-only wrapper futures in `core/tests/common/test_codex.rs` and `core/tests/suite/compact_resume_fork.rs`, which sit directly on top of the same path. - Restored `compact_resume_after_second_compaction_preserves_history` in `core/tests/suite/compact_resume_fork.rs` to a normal `#[tokio::test]` and removed the explicit `TEST_STACK_SIZE_BYTES` thread/runtime sizing. - Simplified a tiny helper in `compact_resume_fork` by making `fetch_conversation_path()` synchronous, which removes one more unnecessary future layer from the test path. ## Verification - `cargo test -p codex-core --test all suite::compact_resume_fork::compact_resume_after_second_compaction_preserves_history -- --exact --nocapture` - `cargo test -p codex-core --test all suite::compact_resume_fork -- --nocapture` - Re-ran the built `codex-core` `tests/all` binary directly with reduced stack sizes: - `RUST_MIN_STACK=917504` passes - `RUST_MIN_STACK=786432` still overflows - `cargo test -p codex-core` - Still fails locally in unrelated existing integration areas that expect the `codex` / `test_stdio_server` binaries or hit the existing `search_tool` wiremock mismatches.
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.
If you want to contribute or inspect behavior in detail, start by reading the module-level README.md files under each crate and run the project workspace from the top-level codex-rs directory so shared config, features, and build scripts stay aligned.