alice starts a session on node-1
  session_start returned HTTP 200, session_id=39489804-51a3-46df-8232-a785476310ec
alice writes 2 memories tagged with session_id
settle 6s for session-tagged fanout
bob lists on node-2 filtered by session_id=39489804-51a3-46df-8232-a785476310ec
  bob sees 2 rows tagged session_id=39489804-51a3-46df-8232-a785476310ec (expected 2)