fcoury-oai
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## TL;DR Fixes the issues when using Codex CLI with Zellij multiplexer. Before this PR there would be no scrollback when using it inside a zellij terminal. ## Problem Addresses #2558 Zellij does not support ANSI scroll-region manipulation (`DECSTBM` / Reverse Index) or the alternate screen buffer in the way traditional terminals do. When codex's TUI runs inside Zellij, two things break: (1) inline history insertion corrupts the display because the scroll-region escape sequences are silently dropped or mishandled, and (2) the composer textarea renders with inherited background/foreground styles that produce unreadable text against Zellij's pane chrome. ## Mental model The fix introduces a **Zellij mode** — a runtime boolean detected once at startup via `codex_terminal_detection::terminal_info().is_zellij()` — that gates two subsystems onto Zellij-safe terminal strategies: - **History insertion** (`insert_history.rs`): Instead of using `DECSTBM` scroll regions and Reverse Index (`ESC M`) to slide content above the viewport, Zellij mode scrolls the screen by emitting `\n` at the bottom row and then writes history lines at absolute positions. This avoids every escape sequence Zellij mishandles. - **Viewport expansion** (`tui.rs`): When the viewport grows taller than available space, the standard path uses `scroll_region_up` on the backend. Zellij mode instead emits newlines at the screen bottom to push content up, then invalidates the ratatui diff buffer so the next draw is a full repaint. - **Composer rendering** (`chat_composer.rs`, `textarea.rs`): All text rendering in the input area uses an explicit `base_style` with `Color::Reset` foreground, preventing Zellij's pane styling from bleeding into the textarea. The prompt chevron (`›`) and placeholder text use explicit color constants instead of relying on `.bold()` / `.dim()` modifiers that render inconsistently under Zellij. ## Non-goals - This change does not fix or improve Zellij's terminal emulation itself. - It does not rearchitect the inline viewport model; it adds a parallel code path gated on detection. - It does not touch the alternate-screen disable logic (that already existed and continues to use `is_zellij` via the same detection). ## Tradeoffs - **Code duplication in `insert_history.rs`**: The Zellij and Standard branches share the line-rendering loop (color setup, span merging, `write_spans`) but differ in the scrolling preamble. The duplication is intentional — merging them would force a complex conditional state machine that's harder to reason about than two flat sequences. - **`invalidate_viewport` after every Zellij history flush or viewport expansion**: This forces a full repaint on every draw cycle in Zellij, which is more expensive than ratatui's normal diff-based rendering. This is necessary because Zellij's lack of scroll-region support means the diff buffer's assumptions about what's on screen are invalid after we manually move content. - **Explicit colors vs semantic modifiers**: Replacing `.bold()` / `.dim()` with `Color::Cyan` / `Color::DarkGray` / `Color::White` in the Zellij branch sacrifices theme-awareness for correctness. If the project ever adopts a theming system, Zellij styling will need to participate. ## Architecture The Zellij detection flag flows through three layers: 1. **`codex_terminal_detection`** — `TerminalInfo::is_zellij()` (new convenience method) reads the already-detected `Multiplexer` variant. 2. **`Tui` struct** — caches `is_zellij` at construction; passes it into `update_inline_viewport`, `flush_pending_history_lines`, and `insert_history_lines_with_mode`. 3. **`ChatComposer` struct** — independently caches `is_zellij` at construction; uses it in `render_textarea` for style decisions. The two caches (`Tui.is_zellij` and `ChatComposer.is_zellij`) are read from the same global `OnceLock<TerminalInfo>`, so they always agree. ## Observability No new logging, metrics, or tracing is introduced. Diagnosis depends on: - Whether `ZELLIJ` or `ZELLIJ_SESSION_NAME` env vars are set (the detection heuristic). - Visual inspection of the rendered TUI inside Zellij vs a standard terminal. - The insta snapshot `zellij_empty_composer` captures the Zellij-mode render path. ## Tests - `terminal_info_reports_is_zellij` — unit test in `terminal-detection` confirming the convenience method. - `zellij_empty_composer_snapshot` — insta snapshot in `chat_composer` validating the Zellij render path for an empty composer. - `vt100_zellij_mode_inserts_history_and_updates_viewport` — integration test in `insert_history` verifying that Zellij-mode history insertion writes content and shifts the viewport. --------- Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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. If you provide both a prompt argument and piped stdin, Codex appends stdin as a <stdin> block after the prompt so patterns like echo "my output" | codex exec "Summarize this concisely" work naturally. 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".
In workspace-write, Codex also includes ~/.codex/memories in its writable roots so memory maintenance does not require an extra approval.
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.