alice writes claim: "sky-color-d6b18911 is blue" on node-1
bob writes contradicting claim: "sky-color-d6b18911 is red" on node-2
  alice.id=fe4ab13c-d2dc-4c7d-94a0-6a992a65af23 bob.id=a2abc495-c989-43b4-a782-282e75a111b0
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