phase A: ai:alice writes handoff to ai:bob (uuid=h-204fc54e5f6c4f8da315316ab67cc874)
settle 8s for quorum fanout
phase B: ai:bob reads handoff on node-2
  ai:bob sees 1 handoff memories from ai:alice
phase C: ai:bob writes acknowledgement (uuid=a-0c961a584159470292b7fe78822c5646)
settle 8s for reverse-direction fanout
phase D: ai:alice reads ack on node-1
  ai:alice sees 1 ack memories from ai:bob