phase A: ai:alice writes handoff to ai:bob (uuid=h-621dcfcbe9f24a78a43c72bf37a131d8)
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-6a3754d2507a44e5b3828639b655f3df)
settle 8s for reverse-direction fanout
phase D: ai:alice reads ack on node-1
  ai:alice sees 1 ack memories from ai:bob