alice writes claim: "sky-color-9df07593 is blue" on node-1
bob writes contradicting claim: "sky-color-9df07593 is red" on node-2
  alice.id=329b19ca-4974-438b-8a95-f2dde1b09850 bob.id=cce5a1cf-4919-4601-98f4-1b925946c956
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