## Why
Reasoning summaries need to retain their position among computer actions and exploration commands, including when they arrive before a running call completes.
## What changed
Share ordered call and reasoning storage through `ActivityGroup` and let history cells accept reasoning through `append_reasoning`. Computer activity and exploration groups now retain reasoning while calls are running, showing it in order in the expanded transcript while keeping compact previews and raw output free of reasoning.
## Testing
Add regression snapshots for reasoning during a follow-up exploration command and for computer activity with multiple intervening and trailing summaries. Verify identical live and replayed computer activity across compact, expanded, and raw output.
GitOrigin-RevId: 92607b38fd4b0379616c1ae50b5da1068c8534c3
de33f2d22a