- Implemented gRPC-based tunnel sessions for multiplexing HTTP requests via `grpcTunnelSession` with features like `recvLoop`, `send`, and per-stream state management.
- Registered and unregistered tunnels for domains, replacing DTLS-based sessions for improved scalability and maintainability.
- Integrated domain validation checks during gRPC tunnel handshake with configurable validator support.
- Modified static error pages (`400.html`, `404.html`, `502.html`, `504.html`, `500.html`, `525.html`) to include favicon linking, enhancing error page presentation.
- Introduced handling for `502 Bad Gateway` errors with a dedicated HTML template.
- Updated `writeErrorPage` logic to include 502 and other new status mappings for custom templates.
- Improved error page rendering by mapping 4xx/5xx status codes to appropriate templates.
