alice starts a session on node-1
  session_start returned HTTP 200, session_id=5646146c-a3bb-4bd0-8493-7e6384893d24
alice writes 2 memories tagged with session_id
settle 6s for session-tagged fanout
bob lists on node-2 filtered by session_id=5646146c-a3bb-4bd0-8493-7e6384893d24
  bob sees 2 rows tagged session_id=5646146c-a3bb-4bd0-8493-7e6384893d24 (expected 2)