## What changed
- Add nullable `startedAtMs` and `completedAtMs` fields to `ThreadItem` in live notifications and turn history. Values are Unix milliseconds when recorded.
- Preserve recorded item times through history reconstruction, pagination, and resume, including command start times recorded during approval.
- Separate the Rust item payload into `ThreadItemPayload` while keeping the JSON payload flat, and update consumers, schemas, and generated TypeScript and Python types.
## Testing
Extend coverage for timestamp serialization, history reconstruction, paginated reads and resume, and persisted Python SDK items.
GitOrigin-RevId: ecbcee95af52db7c807b46a6e9deb30e5fba1f80