alice writes M1 content=v1-1fc1c8daa94246f28b54a30047fff6df on node-1
  M1 id=4432d1ac-763c-4faf-bbf9-ec87825c447b
settle 5s for initial replication
bob updates M1 content=v2-746f47f211874325a34c6e66b75b08be 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="v2-746f47f211874325a34c6e66b75b08be" agent_id="ai:alice"