alice writes claim: "sky-color-ab3cf6d7 is blue" on node-1
bob writes contradicting claim: "sky-color-ab3cf6d7 is red" on node-2
  alice.id=55ff4daf-ab0c-4f66-b592-06377918d1dc bob.id=20f7ac34-c2c1-4fb5-989b-e4a84b006c03
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