alice starts a session on node-1
  session_start returned HTTP 200, session_id=0bc75ca8-7616-436c-8b48-412b0ea6ece2
alice writes 2 memories tagged with session_id
settle 6s for session-tagged fanout
bob lists on node-2 filtered by session_id=0bc75ca8-7616-436c-8b48-412b0ea6ece2
  bob sees 2 rows tagged session_id=0bc75ca8-7616-436c-8b48-412b0ea6ece2 (expected 2)