alice starts a session on node-1
  session_start returned HTTP 200, session_id=c0bf4d3a-d831-4085-b735-0d1a6f7bba69
alice writes 2 memories tagged with session_id
settle 6s for session-tagged fanout
bob lists on node-2 filtered by session_id=c0bf4d3a-d831-4085-b735-0d1a6f7bba69
  bob sees 2 rows tagged session_id=c0bf4d3a-d831-4085-b735-0d1a6f7bba69 (expected 2)