## Why
Attached threads need inherited context for model requests while exposing only their own turns to clients. Parent turns and token usage should not appear as activity in an empty attached thread.
## What changed
- Stop attached-thread history traversal at the parent boundary, including after reverts, and hide inherited interruption markers.
- Apply visible-history boundaries to search, realtime timelines, and turn-specific fork and revert requests.
- Suppress inherited token-usage replay on paginated fork resumes, require fork replay to reference a returned turn, and skip empty turn IDs.
- Require a paginated source for `thread/fork` with `attachToSource` and update the protocol documentation.
## Testing
Extend regression coverage for attached-thread restart and database recovery, retained parent context in model requests, child-only history, mid-turn fork boundaries, legacy-source rejection, and suppression of parent token-usage notifications.
GitOrigin-RevId: 67858caf3bb74b7e79d4dd59bed9c61055fe0ff1
Brent Traut
766f5473f2