Review round 1:
- Rejected work discarded before a restore completes the queue's adoption,
  so its replacement ops are not skipped.
- The restore waits for its page add's ack behind other batches, and takes
  the page as its base only when it came back empty: a page a teammate
  restored first is never read as deletions here.
- A page whose images this device cannot upload again is not restored.
- Discard waits for ops already sent for the page, then withdraws what
  they left; while any remain, the choice stays open.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>