alice starts a session on node-1
  session_start returned HTTP 200, session_id=fe5a2124-d0c3-4cfb-83b7-a122f6addd14
alice writes 2 memories tagged with session_id
settle 6s for session-tagged fanout
bob lists on node-2 filtered by session_id=fe5a2124-d0c3-4cfb-83b7-a122f6addd14
  bob sees 2 rows tagged session_id=fe5a2124-d0c3-4cfb-83b7-a122f6addd14 (expected 2)