alice writes claim: "sky-color-34dc6450 is blue" on node-1
bob writes contradicting claim: "sky-color-34dc6450 is red" on node-2
  alice.id=46bbe8e5-5333-419d-957c-1542a82aaf65 bob.id=7d027d6f-f133-4784-8623-d42846a95095
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