phase A: ai:alice writes handoff to ai:bob (uuid=h-3ac9c14c9f274e1390a144b1b3ce4c43)
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-d39149f2c25b45659f97749a6e2c0e35)
settle 8s for reverse-direction fanout
phase D: ai:alice reads ack on node-1
  ai:alice sees 1 ack memories from ai:bob