Presence

When lease.presence is true (default), each daemon holds presence.<nodeID> (default TTL 3s).

If that lease expires, the leader removes the node (member.left). Heartbeats are the slower backup (interval 2s, timeout 1s, 3 misses).

Observers hold presence like voters so they disappear from the list when they die. Expiry uses RemoveServer (works for voters and observers).