alice writes M1 content=d-a3e61579afbc4a219c76ec2a79b73071 on node-1
  created memory id=977388f0-89e8-4bfc-af9c-886ece0ff9f1
settle 8s for pre-delete fanout
pre-delete: verifying M1 is visible on all peers
  pre-delete node-2 sees 1
  pre-delete node-3 sees 1
  pre-delete node-4 sees 1
alice deletes M1 on node-1
  DELETE returned HTTP 200
settle 15s for tombstone propagation
post-delete: verifying M1 is GONE from all peers
  post-delete node-2 sees 0 (expected 0)
  post-delete node-3 sees 0 (expected 0)
  post-delete node-4 sees 0 (expected 0)