The post-import background deduplication pass (a merge-DELETE writer,
debounced ~5 minutes after import) had four lifecycle defects:
- enableDeduplication: false did not gate the background schedule — an
import that explicitly opted out could still have entities auto-removed
minutes later. The flag now gates both the inline and background passes.
- Each import() constructed its own coordinator-owned deduplicator, so the
debounce never spanned imports (N imports = N delete timers). The brain
now owns a single lazy instance (getBackgroundDeduplicator).
- close() never cancelled pending dedup; a delete pass could fire against
a closed brain. close() now cancels it first.
- The 5-minute timer held the process open (exit-hang class); now unref'd.
Four regression tests pin the contract (background-dedup-lifecycle);
import guides document that false disables both passes.
