alice starts a session on node-1
  session_start returned HTTP 200, session_id=d0059e72-aa4c-4315-bfd5-2b2d82d51af1
alice writes 2 memories tagged with session_id
settle 6s for session-tagged fanout
bob lists on node-2 filtered by session_id=d0059e72-aa4c-4315-bfd5-2b2d82d51af1
  bob sees 2 rows tagged session_id=d0059e72-aa4c-4315-bfd5-2b2d82d51af1 (expected 2)