alice writes claim: "sky-color-02e67678 is blue" on node-1
bob writes contradicting claim: "sky-color-02e67678 is red" on node-2
  alice.id=d84eb815-24a1-434a-8420-957bddd9b637 bob.id=9bcf001b-c465-454d-b005-f1b85a5ce4e1
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