After `ThinkingComplete` the finalized thinking entry sits in
`app.active_cell` with `streaming = false` until the active cell
flushes to history at end-of-turn. During that window the transcript
rendered the "thinking collapsed; press Ctrl+O for full text"
affordance from `render_thinking`, but `open_thinking_pager` only
searched `app.history` — so the handler surfaced "No thinking blocks
to expand" while pointing at the affordance. The affordance was
truthful; the handler was lying.
Routed the lookup through `cell_at_virtual_index` /
`virtual_cell_count`, the existing virtual-index API that
`open_tool_details_pager` already uses for the same active-cell
window. The selection-based path resolves through the virtual index
too, so dragging into an in-flight thinking block and pressing
Ctrl+O now works as well.
Regression guard: `open_thinking_pager_finds_thinking_in_active_cell`
drives the entry into active_cell, finalizes it so the "collapsed"
affordance is what render_thinking emits, then asserts Ctrl+O pushes
the Pager view instead of surfacing the "No thinking blocks" status.
Hunter Bown
dc2433a8b5