alice writes M1 content=v1-e33170c5f5e041d1a1d0c24523dfa174 on node-1
  M1 id=7628e19c-bf3e-4f27-9338-0d4c3c63c9b5
settle 5s for initial replication
bob updates M1 content=v2-ca68a148bdc74c41995727fecc137d3e 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-ca68a148bdc74c41995727fecc137d3e" agent_id="ai:alice"