The kanban notifier was re-firing the same blocked/gave_up/crashed/timed_out
notifications on every 5-second tick. Root cause: after delivering a terminal
event, the notifier unsubscribed the subscription, deleting its cursor. If
the unsub failed (WAL contention, transient error), the subscription survived
with a stale cursor, and the next tick would re-deliver the same event.
Even when the unsub succeeded, the subscription was gone. If the task later
transitioned to a different state (e.g., blocked -> unblocked -> blocked
again), a new subscription would start at cursor=0, re-delivering all past
events.
Fix: stop unsubscribing on terminal event kinds. Only remove the subscription
when the task reaches a truly final status (done/archived). For blocked,
gave_up, crashed, and timed_out, the subscription stays alive and the cursor
mechanism deduplicates naturally -- events with id <= last_event_id are never
re-fetched. This makes the dedup idempotent and eliminates the re-fire bug.
The old concern about subscriptions leaking forever on blocked tasks is moot:
blocked tasks will eventually be unblocked (transitioning to ready/running)
or archived, at which point the subscription is cleaned up.
a96dd54872