- remove sock_transport, transport abstraction, active connections API
- simplify proxy_conn to 13 fields (was 15), remove tcp_proxy_mapping linked list
- new protocol: stream_id 4B, seq 2B cyclic, HDR_SIZE 8B
- add ERROR subcmd for immediate abort, CLOSE for graceful half-close
- proper half-close: shutdown SHUT_WR, keep reading, no timer
- exhaustive DEBUG_ERROR/WARN on all error/unusual branches
- config parser: report unknown options with filename:line and valid keys
- UDP proxy: datagram relay client↔exit over ETCP
- ICMP proxy: echo ping relay client↔exit over ETCP
- Move via_node_id from per-forward-mapping to global tcp_proxy setting
- Support multiple concurrent tcp_proxy instances (no singleton g_tcp_proxy)
- Cap handshake padding to stay within 1472+overhead
- Handle non-TCP packets (UDP/ICMP) in tcp_proxy raw/tun input paths
- Add utun_instance_create_from_str() for test config creation
Evgeny