## What changed
- Skip threads whose rollout files cannot be found while continuing through
database pages until the requested number of valid threads is collected.
- Retain the skipped threads and their rollout paths in the state database
instead of deleting their metadata during listing.
## Testing
- Update the state-backed listing test to verify that a missing rollout path
does not consume a page slot or remove the stored thread metadata.
GitOrigin-RevId: 51c03a78434b0aeeb5a2dc685b97243b6ad958bf