alice writes M1 content=v1-d7a3ca6775d04dc190aa59c523c323d0 on node-1
  M1 id=83ebb23e-c4e5-49b4-b32f-241c6a0103dd
settle 5s for initial replication
bob updates M1 content=v2-de8068e08b104f2f822cd4bda9bb6d3c on node-2 via PUT
  PUT returned HTTP 200
settle 8s for update fanout
charlie reads M1 on node-3 and checks content + provenance
  charlie sees content="v2-de8068e08b104f2f822cd4bda9bb6d3c" agent_id="ai:alice"