## Why
Collaboration can resume an archived descendant without unarchiving its
rollout. Archiving the parent again previously skipped shutdown for that
descendant because only rollouts newly marked as archived were prepared.
## What changed
Prepare every loaded thread in the spawn subtree for archival, including
descendants whose rollouts are already archived, before updating archive
state.
## Testing
Add an app-server integration test that resumes an archived child through its
parent and verifies that archiving the parent unloads the entire subtree.
GitOrigin-RevId: aca8c0d6ddb8900aad16becbeb594426cea1e3a6
Owen Lin
a1d4aea265