alice writes 4 memories
settle 6s for pre-gc replication
alice forgets 2 via /api/v1/forget
  forget returned HTTP 400
settle 5s for forget propagation
bob triggers /api/v1/gc on node-2
  gc returned HTTP 200
settle 8s for post-gc settle
verify remaining 2 markers are still readable on every peer
  node-1 sees 2/2 live markers
  node-2 sees 2/2 live markers
  node-3 sees 2/2 live markers
  node-4 sees 2/2 live markers