agent: Improve compaction UX (#58913)

Makes it so that we show "Compaction cancelled" when the user interrupts
generation.
Also fixes another small issue where the chevron of the expanded state
would not reflect if it is expanded/collapsed while there is no summary
yet.

Release Notes:

- N/A
e17e272d24Bennet Bo Fenner committed on 6/9/2026, 11:34:38 AM· committed by GitHubparent9baefe7
3 files changedLine totals unavailable