alice starts a session on node-1
  session_start returned HTTP 200, session_id=b19cf954-8847-4456-b839-2260444bf17c
alice writes 2 memories tagged with session_id
settle 6s for session-tagged fanout
bob lists on node-2 filtered by session_id=b19cf954-8847-4456-b839-2260444bf17c
  bob sees 2 rows tagged session_id=b19cf954-8847-4456-b839-2260444bf17c (expected 2)