alice writes claim: "sky-color-88920254 is blue" on node-1
bob writes contradicting claim: "sky-color-88920254 is red" on node-2
  alice.id=299bbcc5-8229-4719-b12b-e80e46dc5afa bob.id=9f8f9abb-a67a-4ba2-a674-2980c1330e94
settle 10s for quorum fanout + contradiction indexing
charlie queries /api/v1/contradictions on node-3
  HTTP 200
  sees both memories: True; sees contradicts link: True