## Summary
- wrap OSC 9 notifications in tmux's DCS passthrough so terminal
notifications make it through tmux
- use codex-terminal-detection for OSC 9 auto-selection so tmux sessions
inherit the underlying client terminal support
- add focused notification backend tests for plain OSC 9 and
tmux-wrapped output
## Stack
- base PR: #18479
- review order: #18479, then this PR
## Why
Tmux does not forward OSC 9 notifications directly; the sequence has to
be wrapped in tmux's DCS passthrough envelope. Codex also had local
notification heuristics that could miss supported terminals when running
under tmux, even though codex-terminal-detection already knows how to
attribute tmux sessions to the client terminal.
## Validation
- `just fmt`
- `cargo test -p codex-tui` *(currently blocked by an unrelated existing
compile error in `app-server/src/message_processor.rs:754` referencing
`connection_id` out of scope; not caused by this change)*
Co-authored-by: Codex <noreply@openai.com>
## 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>
- Move core/src/terminal.rs and its tests into a standalone
terminal-detection workspace crate.
- Update direct consumers to depend on codex-terminal-detection and
import terminal APIs directly.
---------
Co-authored-by: Codex <noreply@openai.com>
