CacheBackingStore.Refuse reloads the refused and moved keys through Loaded and only
then unstages them, or changes nothing; RefuseForeign calls it. A write into a store
that holds or would hold a variant lands only while the durable record headers equal
what this store last read (_lastRead), else CultWriteConflictException. SameStoredIdentity
is the one identity predicate.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
