## 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>
Addresses #16560
Problem: `/status` stopped showing the source thread id in forked TUI
sessions after the app-server migration.
Solution: Carry fork source ids through app-server v2 thread data and
the TUI session adapter, and update TUI fixtures so `/status` matches
the old TUI behavior.
Recently, I merged a number of PRs to increase startup timeouts for
scripts that ran under PowerShell, but in the failure for
`suite::codex_tool::test_shell_command_approval_triggers_elicitation`, I
found this in the error logs when running on Bazel with BuildBuddy:
```
[mcp stderr] 2026-04-02T19:54:10.758951Z ERROR codex_core::tools::router: error=Exit code: 1
[mcp stderr] Wall time: 0.2 seconds
[mcp stderr] Output:
[mcp stderr] 'New-Item' is not recognized as an internal or external command,
[mcp stderr] operable program or batch file.
[mcp stderr]
```
This error implies that the command was run under `cmd.exe` instead of
`pwsh.exe`. Under GitHub Actions, I suspect that the `%PATH%` that is
passed to our Bazel builder is scrubbed such that our tests cannot find
PowerShell where GitHub installs it. Having these explicit fallback
paths should help.
While we could enable these only for tests, I don't see any harm in
keeping them in production, as well.
rhan-oai