## Why
Clients need to mark threads read or unread without overwriting unseen results or another window's explicit mark.
## What changed
Add `thread/readState/update` for eligible durable local threads, gated by `initialize.capabilities.experimentalApi`. Requests include `threadId`, `expectedRevision`, and an operation of `{type:"read"}` or `{type:"unread"}`.
Marking read clears `firstUnread`; marking unread sets it to `threadStart`. Successful updates return the read state and notify subscribers through `thread/readState/changed`. Both operations require an exact revision match. Stale requests return `-32600` with `readStateConflict` and the current read state, requiring a fresh user action rather than a blind retry. Updates do not change thread recency.
## Testing
Add app-server coverage for experimental capability gating, explicit unread marks and notifications, conflicts for both stale operations, and marking read with a fresh revision.
GitOrigin-RevId: 775f6e9584dc91bd3c2ee9a309144b5baf0edffa
## What changed
Add the experimental `thread/readState/changed` notification with `threadId` and the committed `readState` receipt. Send it to existing thread subscribers when terminal activity updates read state or a revert clears a removed unread position. Emit terminal read-state updates before `turn/completed` so completion remains the last notification for that result.
Expose the notification in generated JSON schemas, TypeScript types, and Python SDK models. Document experimental capability gating, subscription lifetime, notification opt-out, and refreshing receipts when concurrent responses disagree.
## Testing
Extend the read-state integration test to assert that the notification receipt matches the receipt returned by `thread/read` after terminal activity.
GitOrigin-RevId: 28935352a881b7a5e2e7f629173c3b2061bd7941
## 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
Brent Traut