## 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
## What changed
- Add `attachToSource` to `thread/fork` to persist a fork attached to its source without emitting `thread/started`. Attached forks require local storage and cannot use `ephemeral` or `deferGoalContinuation`.
- Hide attached threads from ordinary listings and add `attachedToThreadId` to `thread/list` for explicit discovery, including empty threads. Keep this relationship separate from spawned-agent parent and ancestor filters.
- Persist attachment metadata in rollouts and SQLite so it survives restarts and database recovery. Reject source deletion until its attached threads are deleted.
## Testing
Add coverage for legacy and paginated history, restart and missing or corrupt database recovery, filtered listings and pagination, resume, conflicting options, and deletion safeguards across store instances.
GitOrigin-RevId: 589f3174fc36f6054e75d65818360695645a5913
Brent Traut