alice writes claim: "sky-color-5213d3ca is blue" on node-1
bob writes contradicting claim: "sky-color-5213d3ca is red" on node-2
  alice.id=e98920e5-9a69-46d2-9693-c78342fbbe12 bob.id=5ac1692c-f1d2-491b-ae9b-f8184e037b54
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