alice starts a session on node-1
  session_start returned HTTP 200, session_id=bb138f3d-8a03-4e2e-8e23-906de037695e
alice writes 2 memories tagged with session_id
settle 6s for session-tagged fanout
bob lists on node-2 filtered by session_id=bb138f3d-8a03-4e2e-8e23-906de037695e
  bob sees 2 rows tagged session_id=bb138f3d-8a03-4e2e-8e23-906de037695e (expected 2)