filer: take the listing snapshot as a claim below later and unfinished stamps
A ListEntries snapshot tells the client that every event at or below it is
already in the listing, so the mount drops those events from a directory
build and fences them with the directory floor. The snapshot was a raw
time.Now(), which an event stamp can tie on a coarse clock: on Windows a
mkdir right after a listing of its parent was stamped with the snapshot's
own timestamp, the mount took it as listed, and the new directory stayed
missing from a parent marked cached. A create stamped before the snapshot
but not yet in the store was dropped the same way.
Take the snapshot through the same in-flight claim the idle heartbeat uses:
it stays below every unfinished stamp, and every later stamp lands above it.
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>