With the unique per-writer temp suffix, a rename ENOENT can no longer mean "a
concurrent idempotent writer already renamed it" — nobody else holds this
writer's temp. It means our just-written temp vanished before the rename, so the
bytes did NOT land. The old code returned success on that ENOENT, acknowledging
a write that persisted nothing; the native provider mmaps these blobs, so a
phantom-acked blob is a silent-loss.
saveBinaryBlob now retries once with a fresh temp (self-healing a transient
external-sweeper/crash-cleanup race), and if the temp vanishes again it throws
loud rather than acknowledging a store-nothing write. Non-ENOENT rename faults
propagate verbatim as before. The unique-temp suffix already eliminated the
concurrent same-key collision that originally motivated the ENOENT shortcut.
