FrankenPHP before 1.13.4 Cross-Request Response Header Leak in Worker Mode

FrankenPHP before 1.13.4 contains an information disclosure vulnerability in worker mode that fails to clear last HTTP stream response headers between requests, because the reset only happens in RSHUTDOWN, which worker requests skip. Later requests calling http_get_last_response_headers() can read headers fetched by earlier requests on the same worker thread, exposing other users' Set-Cookie or token headers from backend APIs.