## What changed
- Add experimental `readState` to `thread/read` and a thread-ID-keyed `readStates` map to `thread/list` for eligible durable local user threads. Each receipt contains `firstUnread` and an opaque `revision`.
- Publish new visible terminal results before `turn/completed`, after flushing the rollout. Reading snapshots leaves activity unread; replayed history does not publish new activity.
- Clear unread positions removed by a paginated thread revert while preserving explicit thread-start marks and concurrent receipt updates.
## Testing
Add an integration test covering completed-turn receipts, repeated reads without acknowledgement, matching list receipts, and revert cleanup with a changed revision.
GitOrigin-RevId: e7f6ddfbb1fc2fa95d1ef2876d7f0f7b9f99ff65
