phase A: ai:alice writes handoff to ai:bob (uuid=h-1e4d4dcbd85e41b4a4c4420bf59ac021)
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-7ac7e2f413df48eb8b6b99d8fd385e44)
settle 8s for reverse-direction fanout
phase D: ai:alice reads ack on node-1
  ai:alice sees 1 ack memories from ai:bob