fix: Correct the URL scheme and port used on the psc_endpoint branch in Sandboxes.send_command and Sandboxes.generate_browser_ws_headers. The branch added in cl/981254234 built https://{psc_endpoint} and defaulted to port 443, but PSC endpoints for VPC-SC sandboxes route directly to the sandbox router pod, which serves plain HTTP on the caller-supplied port (default 8080) and does not terminate TLS on 443. As a result every VPC-SC data-plane call through the SDK hung on ConnectTimeout at HTTPSConnectionPool(host='<psc-ip>', port=443). The endpoint is now built as http://{psc_endpoint}:{port} for send_command and ws://{psc_endpoint}:{port} for generate_browser_ws_headers, so the URL matches what the router serves. Non-VPC-SC callers (load_balancer_hostname / load_balancer_ip branches) are unaffected. - #7236