alice writes claim: "sky-color-48c37bcc is blue" on node-1
bob writes contradicting claim: "sky-color-48c37bcc is red" on node-2
  alice.id=a3cb4c2a-3c06-41cc-a8e4-fc417aa27749 bob.id=a0877a28-3c65-44dc-b16d-2fd145e86392
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