alice starts a session on node-1
  session_start returned HTTP 200, session_id=783e1874-2298-4f46-acf5-4e767c8f3dde
alice writes 2 memories tagged with session_id
settle 6s for session-tagged fanout
bob lists on node-2 filtered by session_id=783e1874-2298-4f46-acf5-4e767c8f3dde
  bob sees 2 rows tagged session_id=783e1874-2298-4f46-acf5-4e767c8f3dde (expected 2)