phase A: ai:alice writes handoff to ai:bob (uuid=h-c03a3fd146ff40d195e34d99541a6341)
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-cddb5cee4cc748a39c5b43dfbd556fb9)
settle 8s for reverse-direction fanout
phase D: ai:alice reads ack on node-1
  ai:alice sees 1 ack memories from ai:bob