alice starts a session on node-1
  session_start returned HTTP 200, session_id=c8bbed4e-8c8a-4986-a8f6-32408a57dd20
alice writes 2 memories tagged with session_id
settle 6s for session-tagged fanout
bob lists on node-2 filtered by session_id=c8bbed4e-8c8a-4986-a8f6-32408a57dd20
  bob sees 2 rows tagged session_id=c8bbed4e-8c8a-4986-a8f6-32408a57dd20 (expected 2)