alice writes claim: "sky-color-8621b8fe is blue" on node-1
bob writes contradicting claim: "sky-color-8621b8fe is red" on node-2
  alice.id=3d94d251-7eff-4e94-9ee9-74f221a24493 bob.id=f7453a0f-b313-4183-a1b1-f1d884c31c3e
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