## What changed
Allow `cursor` to accept an item anchor such as `{"type":"item","itemId":"item-123"}` with a non-empty `turnId`. Ascending pagination returns items after the anchor; descending pagination returns items before it. The anchor itself is excluded, and subsequent pages use the returned opaque string cursor.
Resolve anchors within the requested turn's visible history, including inherited fork history. Reject missing turn IDs and empty, unknown, or out-of-scope item IDs with invalid params (`-32602`). Preserve existing string and null cursor behavior, and update the protocol schemas, TypeScript and Python types, and API documentation.
## Testing
Add protocol round-trip and invalid-shape tests, app-server coverage for anchored pagination and errors, and thread-store coverage for growing turns, reverse pagination, page boundaries, fork visibility, and anchor scope validation.
GitOrigin-RevId: a74cea190d3ff1b44865429f8b0650b793eb688d
## What changed
- Make `thread/turns/list`, `thread/items/list`, and `thread/revert` available
without the experimental API capability.
- Stabilize `thread/reverted`, `thread.historyMode`, and the pagination fields
used by `thread/resume` and `thread/fork`.
- Publish the promoted requests, responses, and fields in the stable JSON and
TypeScript schemas, and update the app-server documentation accordingly.
GitOrigin-RevId: 18b8c53c265211597bb1a62fd62f66f4a3df5f06
Brent Traut