feat(tui): add terminal title support to tui app server

[fcoury]

TR;DR

Replicates the /title command from tui to tui_app_server.

Problem

The classic tui crate supports customizing the terminal window/tab title via /title, but the tui_app_server crate does not. Users on the app-server path have no way to configure what their terminal title shows (project name, status, spinner, thread, etc.), making it harder to identify Codex sessions across tabs or windows.

Mental model

The terminal title is a status surface -- conceptually parallel to the footer status line. Both surfaces are configurable lists of items, both share expensive inputs (git branch lookup, project root discovery), and both must be refreshed at the same lifecycle points. This change ports the classic tui's design verbatim:

1. terminal_title.rs owns the low-level OSC write path and input sanitization. It strips control characters and bidi/invisible codepoints before placing untrusted text (model output, thread names, project paths) inside an escape sequence.

2. title_setup.rs defines TerminalTitleItem (the 8 configurable items) and TerminalTitleSetupView (the interactive picker that wraps MultiSelectPicker).

3. status_surfaces.rs is the shared refresh pipeline. It parses both surface configs once per refresh, warns about invalid items once per session, synchronizes the git-branch cache, then renders each surface from the same StatusSurfaceSelections snapshot.

4. chatwidget.rs sets TerminalTitleStatusKind at each state transition (Working, Thinking, Undoing, WaitingForBackgroundTerminal) and calls refresh_terminal_title() whenever relevant state changes.

5. app.rs handles the three setup events (confirm/preview/cancel), persists config via ConfigEditsBuilder, and clears the managed title on Drop.

Non-goals

• Restoring the previous terminal title on exit. There is no portable way to read the terminal's current title, so Drop clears the managed title rather than restoring it.
• Sharing code between tui and tui_app_server. The implementation is a parallel copy, matching the existing pattern for the status-line feature. Extracting a shared crate is future work.

Tradeoffs

• Duplicate code across crates. The three core files (terminal_title.rs, title_setup.rs, status_surfaces.rs) are byte-for-byte copies from the classic tui. This was chosen for consistency with the existing status-line port and to avoid coupling the two crates at the dependency level. Future changes must be applied in both places.

• status_surfaces.rs is large (~660 lines). It absorbs logic that previously lived inline in chatwidget.rs (status-line refresh, git branch management, project root discovery) plus all new terminal-title logic. This consolidation trades file size for a single place where both surfaces are coordinated.

• Spinner scheduling on every refresh. The terminal title spinner (when active) schedules a frame every 100ms. This is the same pattern the status-indicator spinner already uses; the overhead is a timer registration, not a redraw.

Architecture

/title command
  -> SlashCommand::Title
  -> open_terminal_title_setup()
  -> TerminalTitleSetupView (MultiSelectPicker)
  -> on_change:  AppEvent::TerminalTitleSetupPreview  -> preview_terminal_title()
  -> on_confirm: AppEvent::TerminalTitleSetup         -> ConfigEditsBuilder + setup_terminal_title()
  -> on_cancel:  AppEvent::TerminalTitleSetupCancelled -> cancel_terminal_title_setup()

Runtime title refresh:
  state change (turn start, reasoning, undo, plan update, thread rename, ...)
  -> set terminal_title_status_kind
  -> refresh_terminal_title()
  -> status_surface_selections()  (parse configs, collect invalids)
  -> refresh_terminal_title_from_selections()
     -> terminal_title_value_for_item() for each configured item
     -> assemble title string with separators
     -> skip if identical to last_terminal_title (dedup OSC writes)
     -> set_terminal_title() (sanitize + OSC 0 write)
     -> schedule spinner frame if animating

Widget replacement:
  replace_chat_widget_with_app_server_thread()
  -> transfer last_terminal_title from old widget to new
  -> avoids redundant OSC clear+rewrite on session switch

Observability

• Invalid terminal-title item IDs in config emit a one-per-session warning via on_warning() (gated by terminal_title_invalid_items_warned AtomicBool).
• OSC write failures are logged at tracing::debug level.
• Config persistence failures are logged at tracing::error and surfaced to the user via add_error_message().

Tests

• terminal_title.rs: 4 unit tests covering sanitization (control chars, bidi codepoints, truncation) and OSC output format.
• title_setup.rs: 3 tests covering setup view snapshot rendering, parse order preservation, and invalid-ID rejection.
• chatwidget/tests.rs: Updated test helpers with new fields; existing tests continue to pass.

[Copilot]

Pull request overview

Adds configurable terminal title support to the tui_app_server, including a /title setup UI, persistence, and runtime OSC title updates driven by shared “status surface” rendering logic.

Changes:

• Introduce low-level OSC terminal-title writer with sanitization and tests.
• Add /title slash command and a bottom-pane picker to configure/preview title segments, persisting selection to config.
• Refactor shared status-line + terminal-title rendering/state (git branch lookup, invalid-item warnings, caches) into chatwidget/status_surfaces.rs, and attempt to preserve the last-written title cache across widget replacement.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
codex-rs/tui_app_server/src/terminal_title.rs	New OSC title writer + sanitization and unit tests.
codex-rs/tui_app_server/src/slash_command.rs	Adds Title slash command metadata.
codex-rs/tui_app_server/src/lib.rs	Wires in the new terminal_title module.
codex-rs/tui_app_server/src/chatwidget/tests.rs	Updates ChatWidget test builders for new title/state fields.
codex-rs/tui_app_server/src/chatwidget/status_surfaces.rs	New shared status-line/terminal-title parsing, caching, and rendering.
codex-rs/tui_app_server/src/chatwidget.rs	Integrates terminal title updates, setup flows, and shared refresh entrypoints.
codex-rs/tui_app_server/src/bottom_pane/title_setup.rs	New terminal-title configuration picker UI + snapshot tests.
codex-rs/tui_app_server/src/bottom_pane/snapshots/codex_tui_app_server__bottom_pane__title_setup__tests__terminal_title_setup_basic.snap	Snapshot for the new picker UI.
codex-rs/tui_app_server/src/bottom_pane/mod.rs	Exposes TerminalTitleItem + TerminalTitleSetupView.
codex-rs/tui_app_server/src/app_event.rs	Adds app events for title setup/preview/cancel.
codex-rs/tui_app_server/src/app.rs	Persists title config changes; tries to preserve title cache across widget replacement; clears title on drop.

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[etraut-openai]

Code looks good. I also built and tested it locally.