Warnings in the TUI should show longer

[dgageot]

Ideally, the user has to click on [x] at the top right to close a warning.
If a new one is triggered, it should show behind.

[aheritier]

Additional Analysis

After investigating the codebase, here are detailed findings on this issue.

Root Cause

The notification system in pkg/tui/components/notification/notification.go uses a fixed 3-second auto-dismiss timer (defaultDuration = 3 * time.Second) for all notification types — success, info, warning, and error alike. There is no manual dismiss mechanism and no way to recall past notifications.

This is particularly problematic for warning messages like toolset initialization failures, which can be multi-line and technical:

Some toolsets failed to initialize for agent 'root'.

Details:

- toolset rag failed: failed to create RAG manager: failed to build manager
  config for RAG "rag": failed to build reranking config: failed to resolve
  reranking model "balanced": model "balanced" not found in configuration

Relevant Code

• pkg/tui/components/notification/notification.go — Manager struct, ShowMsg/HideMsg messages, fixed defaultDuration, View() rendering. This is where the timer and dismiss logic lives.
• pkg/tui/page/chat/runtime_events.go — Maps runtime.WarningEvent → notification.WarningCmd() (line 63). Also dispatches warning notifications for model fallback events.
• pkg/runtime/loop.go — emitAgentWarnings() drains agent init warnings and emits WarningEvents. formatToolWarning() builds the multi-line message.
• pkg/runtime/event.go — WarningEvent type definition.
• pkg/tui/styles/styles.go — NotificationWarningStyle, NotificationErrorStyle for visual styling.

Suggested Implementation Approach

1. Manual dismissal (as described in this issue): Add a close button / keybinding (e.g., Esc or d) to dismiss the topmost notification. The HideMsg mechanism already exists — it just needs a keyboard trigger.

2. Scale duration by severity and content length: Rather than one fixed duration, use longer defaults for warnings (8s+) and errors (10s+), with additional time for longer messages (~1s per 15 words).

3. Consider persistent banners for session-impacting warnings: Toolset init failures affect the entire session. A dismissible inline banner (top of chat area or sidebar indicator) would be more appropriate than a transient toast for these cases.

4. Accessibility (WCAG 2.1 SC 2.2.1): Auto-dismissing content without user control fails the "Timing Adjustable" success criterion. Manual dismiss addresses this.

Closing #2249 as duplicate of this issue.