EnqueueAsync used synchronous SQLite I/O (conn.Open / ExecuteNonQuery /
COUNT(*)) on the caller's thread, blocking the alarm-emitting thread under
write contention with the drain worker. The cancellationToken parameter was
silently ignored.
- EnqueueAsync converted to genuine async: OpenAsync / ExecuteNonQueryAsync /
ExecuteScalarAsync used throughout; ct threaded to every await.
- ApplyPragmasAsync added alongside the existing ApplyPragmas helper so
the WAL + busy_timeout PRAGMAs are applied on the async open path too.
- EnforceCapacityAsync added to handle capacity eviction on the async path.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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