alice writes claim: "sky-color-a83db5ab is blue" on node-1
bob writes contradicting claim: "sky-color-a83db5ab is red" on node-2
  alice.id=5094da54-21e0-4ec4-9546-4925ddf6c32d bob.id=dfcc5e93-b00f-4bc0-9396-bfa508f9516d
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