alice starts a session on node-1
  session_start returned HTTP 200, session_id=f7da2b5e-18c2-4a3b-865c-c98fdf93edc7
alice writes 2 memories tagged with session_id
settle 6s for session-tagged fanout
bob lists on node-2 filtered by session_id=f7da2b5e-18c2-4a3b-865c-c98fdf93edc7
  bob sees 2 rows tagged session_id=f7da2b5e-18c2-4a3b-865c-c98fdf93edc7 (expected 2)