Previously CKSyncEngine was created with nil state serialization on
every launch, replaying the entire zone change history (hundreds of
merge/delete log lines and re-downloads each start). Now the saved
state is loaded so launches only fetch changes since the last session.
To make incremental sync safe:
- Clear persisted state once when the record schema version increases,
so records previously skipped as unsupported get re-delivered after
an app update.
- Handle remote zone deletion in fetchedDatabaseChanges by recreating
the zone and re-uploading local data, instead of leaving sync dead.
Account change and manual Refresh Sync still clear the state and force
a full fetch as before.
CloudKitRecordMapper was a standalone actor, so 'await recordMapper.toCKRecord'
from the @MainActor sync engine hopped off the main actor and read live
SwiftData @Model properties (e.g. LocalPlaylistItem.authorName) from the wrong
executor. SwiftData models are bound to the main ModelContext and are not
thread-safe, so this raced the backing store and crashed with EXC_BAD_ACCESS.
Make the mapper @MainActor (it must touch main-isolated models regardless) and
drop the now-redundant awaits. Fixes the crash for all synced model types.
Fixes an EXC_BAD_ACCESS seen in TestFlight build 261.
