alice writes claim: "sky-color-c82e0e4d is blue" on node-1
bob writes contradicting claim: "sky-color-c82e0e4d is red" on node-2
  alice.id=e6b4b425-4480-4508-84c3-2d7ded1e7d09 bob.id=c705194f-3453-4b3e-ae35-8099d5ab5b9b
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