phase A: ai:alice writes handoff to ai:bob (uuid=h-18c8c6d05ba14178a2437884cd4fd553)
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-023f99ca5fcf4c30934cb9a0827a9839)
settle 8s for reverse-direction fanout
phase D: ai:alice reads ack on node-1
  ai:alice sees 1 ack memories from ai:bob