[FEATURE]: Allow TUI plugins to extend built-in dialogs and search #57938

Feature hasn't been suggested before.

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Describe the enhancement you want to request

Summary

Add a supported plugin API to extend built-in TUI dialogs, starting with session search.

Use case

I want to keep session tabs enabled while also pinning sessions in session search. Currently, tab mode hides the built-in pin action and pinned group.

A plugin could provide this behavior, but the documented API only supports creating a separate dialog—not extending the existing session picker. This means duplicating core search and navigation behavior or maintaining a core patch.

Proposed capabilities

Allow plugins to:

• Add actions and keyboard shortcuts for the selected item.
• Add item decorations, such as pin indicators.
• Add groups and customize filtering or result order.
• Refresh dialog content when plugin state changes.

These extensions should use stable item IDs and clean up when the plugin unloads. They should not require access to internal UI components.

Expected outcome

A plugin can add pin/unpin and a “Pinned” group to the existing session search while preserving tabs and built-in search behavior.

Session search is the initial use case, but the same extension model could support other built-in pickers.

Alternatives

• A separate plugin-owned picker duplicates core functionality.
• A core patch requires maintaining a custom build.
• A config option could solve pinning alone, but not the broader extensibility gap.

Environment

• OpenCode: v2.1.2
• OS: Windows NT 10.0.26300.0
• Terminal: TERM=xterm-256color; terminal application not identified