alice writes M1 content=v1-d486debb578548deaf8147a5fa3a5fe4 on node-1
  M1 id=86f9e085-2814-46d5-a56e-6db8e61f8cef
settle 5s for initial replication
bob updates M1 content=v2-ca0e7748437d46f09f3465a8131114cd 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-ca0e7748437d46f09f3465a8131114cd" agent_id="ai:alice"