alice starts a session on node-1
  session_start returned HTTP 200, session_id=b14687d6-9662-471f-9626-26f789bc9784
alice writes 2 memories tagged with session_id
settle 6s for session-tagged fanout
bob lists on node-2 filtered by session_id=b14687d6-9662-471f-9626-26f789bc9784
  bob sees 2 rows tagged session_id=b14687d6-9662-471f-9626-26f789bc9784 (expected 2)