alice starts a session on node-1
  session_start returned HTTP 200, session_id=bdd70002-5edd-4d6a-9fff-4245f2c590e0
alice writes 2 memories tagged with session_id
settle 6s for session-tagged fanout
bob lists on node-2 filtered by session_id=bdd70002-5edd-4d6a-9fff-4245f2c590e0
  bob sees 2 rows tagged session_id=bdd70002-5edd-4d6a-9fff-4245f2c590e0 (expected 2)