- 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 `StatusGatewayTimeout` (504) for server-side timeouts between HopGate and backend.
- Implemented 504 error page with multilingual support.
- Enhanced `bufio.Reader` usage in JSON decoding to prevent "dtls: buffer too small" errors for large payloads.
- Applied request handling improvements for control domain and timeout scenarios.
