Pitch

Surface the actions the user already wants in a discoverable place. Right-click on any transcript cell pops a small menu:

• Copy the cell's text
• Open in editor (if the cell references a file, e.g. apply_patch / read_file results)
• Re-run (for tool cells: re-issue the same tool with the same args)
• Jump to thinking (for tool cells: scroll to the thinking block that produced this call)
• Hide cell (collapse to a one-line summary, expand on click)

Different cell types expose different actions; the menu builder picks based on `HistoryCell` variant.

Implementation sketch

1. Hook `crossterm::MouseEvent::Down(MouseButton::Right, x, y)`.
2. Resolve `(x, y)` to a `HistoryCell` via the existing `line_meta` map in `transcript_cache`.
3. Build menu items per-variant in a new `tui/context_menu.rs`.
4. Render as a small popup overlay (already have `PopupView` chrome).
5. Keyboard-equivalent: `Ctrl+Space` on the focused cell.

Acceptance

• Right-click on a transcript cell opens a context menu.
• Each cell type gets the right menu actions.
• Keyboard fallback (`Ctrl+Space`) works for users without mouse capture.
• Menu dismisses cleanly with Esc / click-outside.