alice starts a session on node-1
  session_start returned HTTP 200, session_id=cfb1d767-432f-4197-8198-68fd7aed3322
alice writes 2 memories tagged with session_id
settle 6s for session-tagged fanout
bob lists on node-2 filtered by session_id=cfb1d767-432f-4197-8198-68fd7aed3322
  bob sees 2 rows tagged session_id=cfb1d767-432f-4197-8198-68fd7aed3322 (expected 2)