alice starts a session on node-1
  session_start returned HTTP 200, session_id=020b95a4-e305-43d2-94b1-bf5d90f5c2dc
alice writes 2 memories tagged with session_id
settle 6s for session-tagged fanout
bob lists on node-2 filtered by session_id=020b95a4-e305-43d2-94b1-bf5d90f5c2dc
  bob sees 2 rows tagged session_id=020b95a4-e305-43d2-94b1-bf5d90f5c2dc (expected 2)