Test all key scenarios for the cache refresh mechanism:
- Delete during refresh: subscription delete is buffered and replayed,
preventing ghost entries from the stale snapshot
- Create during refresh: subscription create is buffered and replayed,
preventing lost entries
- Stale entries removed: entries absent from the filer snapshot are
cleaned from the cache
- Local delete buffered: direct DeleteEntry during refresh is both
applied immediately and replayed after commit
- Local create buffered: direct InsertEntry during refresh is preserved
after snapshot commit
- Cancel discards buffer: CancelRefresh drops buffered events and
resumes normal event processing
- Concurrent deletes (issue #8442 scenario): 1000 concurrent delete
events racing with a stale snapshot all resolve correctly