alice writes claim: "sky-color-74d8a799 is blue" on node-1
bob writes contradicting claim: "sky-color-74d8a799 is red" on node-2
  alice.id=c2351419-98b5-4280-9904-9582d9206fc3 bob.id=20d055ac-af9c-4d3b-9cb9-bb8ea5a37d95
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