review NotificationService

[devhawk]

AI suggested adding code to notificationListener

// Signal all waiters so they re-check the DB after a reconnect. Any
// notification that fired during the connection outage would have been
// missed; waking waiters lets them poll the DB directly rather than
// sleeping out their full timeout.

for (LockConditionPair pair : notificationsMap.values()) {
  pair.lock.lock();
  try {
    pair.condition.signalAll();
  } finally {
    pair.lock.unlock();
  }
}

but I haven't really taken a deep look at how LockConditionPair works or to see if it can be improved.

[devhawk]

fixed by #388