Vibe Textual UI

Conventions for building and styling Textual TUI widgets in Vibe. Apply when working in vibe/cli/, creating or modifying widgets, or writing TCSS.

The Textual TUI is being deprecated in favor of the Rust TUI (vibe/cli-rust/). Every user-visible change made here must also ship in the Rust TUI in the same PR; see "Terminal UI changes" in the Vibe project AGENTS.md (next to pyproject.toml).

Widgets

• For selectable lists, use NavigableOptionList from vibe/cli/textual_ui/widgets/navigable_option_list.py instead of Textual's OptionList. It adds j/k cursor navigation on top of the arrow keys; the bare OptionList only handles arrows.
• Keep feature-specific Textual state and helper functions with the feature's widget package. app.py should orchestrate mounting and message handling, not accumulate feature-local state models, defaulting helpers, or import factories.
• Render tool headers as an explicit verb plus message in every state: progressive wording while a call is running, then a settled verb once any result arrives, including a failure. Preserve result metadata such as (truncated) or (scratchpad) immediately after the message and keep error details in the expandable result body.

TCSS

• When a rule sets color: $text-muted;, pair it with a nested &:ansi { text-style: dim; } so the muted intent survives under ANSI themes.
• Never use ansi_* colors (e.g. ansi_red, ansi_bright_blue). Use Textual theme variables like $primary, $foreground, $surface, $error, etc. — see https://textual.textualize.io/guide/design/. ANSI themes are derived from these variables automatically.
• Keep truncation and overflow behavior declarative in TCSS. Do not add resize handlers or explicit widget-width calculations solely to force an ellipsis; accept clipping or overflow when Textual cannot express the layout reliably.