alice starts a session on node-1
  session_start returned HTTP 200, session_id=e54b0aca-ee04-4f06-94aa-570ea5c46ec4
alice writes 2 memories tagged with session_id
settle 6s for session-tagged fanout
bob lists on node-2 filtered by session_id=e54b0aca-ee04-4f06-94aa-570ea5c46ec4
  bob sees 2 rows tagged session_id=e54b0aca-ee04-4f06-94aa-570ea5c46ec4 (expected 2)