alice writes claim: "sky-color-a02534b9 is blue" on node-1
bob writes contradicting claim: "sky-color-a02534b9 is red" on node-2
  alice.id=19f6df78-8d26-4c33-b5b9-a5dc610449d4 bob.id=b01afa10-99bb-4270-a1e2-2b94f6c740ec
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