Disable wal_autocheckpoint on the main connection; run PASSIVE checkpoints from a
worker_threads worker with its OWN better-sqlite3 handle, escalating to TRUNCATE on a
size high-water or PASSIVE-starvation. Removes the synchronous fsync-heavy checkpoint
from the event loop. Config: walCheckpointIntervalMs/HighWaterMB/StarvationRuns.
Local only — no bump/tag.
