alice writes claim: "sky-color-bac5d71b is blue" on node-1
bob writes contradicting claim: "sky-color-bac5d71b is red" on node-2
  alice.id=c2dbeb55-260b-4dc0-a8b3-7dec7276258a bob.id=344bdd9f-30ae-478e-a015-76ad1cf956fd
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