## Summary
- Adds a new `thread/unarchive` RPC to move archived thread rollouts
back into the active `sessions/` tree.
## What changed
- **Protocol**
- Adds `thread/unarchive` request/response types and wiring.
- **Server**
- Implements `thread_unarchive` in the app server.
- Validates the archived rollout path and thread ID.
- Restores the rollout to `sessions/YYYY/MM/DD/...` based on the rollout
filename timestamp.
- **Core**
- Adds `find_archived_thread_path_by_id_str` helper for archived
rollouts.
- **Docs**
- Documents the new RPC and usage example.
- **Tests**
- Adds an end-to-end server test that:
1) starts a thread,
2) archives it,
3) unarchives it,
4) asserts the file is restored to `sessions/`.
## How to use
```json
{ "method": "thread/unarchive", "id": 24, "params": { "threadId": "<thread-id>" } }
```
## Author Codex Session
`codex resume 019bf158-54b6-7960-a696-9d85df7e1bc1` (soon I'll make this
kind of session UUID forkable by anyone with the right
`session_object_storage_url` line in their config, but for now just
pasting it here for my reference)
62266b13f8