alice writes A on node-1
bob writes B on node-2
polling node-3 for both writes to propagate (max 30 s)
  both writes visible after 1 s
settle 3s for embedder + HNSW catch-up
  node-3 DB embedding probe: 'dawn-walk|1537|BYTES | ridge-strides|1537|BYTES'
charlie queries on node-3 with semantically-related prompt
  recall mode=hybrid returned 2 rows
  charlie sees alice's memory: 1 (expected >=1)
  charlie sees bob's memory: 1 (expected >=1)