## What changed
- Add `context_window_id` to turn metadata for sampling and compaction requests, using the UUID for the model-visible context window.
- Keep the ID stable for requests in the same context window and advance it after compaction, independently of the existing thread-generation `window_id`.
- Reserve `context_window_id` so client metadata cannot override it.
## Testing
- Cover HTTP and WebSocket metadata, remote compaction, token-budget context alignment, resume behavior, and post-compaction window changes.
GitOrigin-RevId: 55cceea377ad509c8dd96ad668f2b5703ea46a63
Brandon Zhang
27c05a52e0