alice starts a session on node-1
  session_start returned HTTP 200, session_id=e037574a-278a-4023-a2f6-3378f3c4803c
alice writes 2 memories tagged with session_id
settle 6s for session-tagged fanout
bob lists on node-2 filtered by session_id=e037574a-278a-4023-a2f6-3378f3c4803c
  bob sees 2 rows tagged session_id=e037574a-278a-4023-a2f6-3378f3c4803c (expected 2)