phase A: ai:alice writes handoff to ai:bob (uuid=h-0eb36c3ff729454da9629b7d972b7d6c)
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-5380e1fcbaf442a3a2cb7e57ec2f0de8)
settle 8s for reverse-direction fanout
phase D: ai:alice reads ack on node-1
  ai:alice sees 1 ack memories from ai:bob