Added #ifdef __cplusplus / extern "C" { ... } / #endif to ~65 headers in src/ and lib/, enabling the C library to be linked into C++ code (chatgui). Fixed packet_dump.h (added missing header guard) and etcp_bbr.h (#pragma once guard).
- New ETCP protocol ETCP_ID_NAT (0x02) for NAT traffic between nodes - eim_nat.c/h: Pure NAT engine (table, port allocation, checksum updates, egress/ingress) - nat_transport.c/h: Transport layer (NAT TUN, ETCP binding, client/provider roles) - route_bgp_find_conn_for_node(): shared utility for optimal connection lookup - tun_init_nat(): dedicated TUN creation for NAT - Config: [nat] section with tun_ip, port_start/end, nat_via, forward rules - Fix: csum_update_ip/transport use htonl() halves (correct on LE systems) - Fix: IP_FRAG_MF_MASK changed to 0x2000 (after ntohs, MF is bit 13) - Tests: 26 engine unit + 4 transport integration + 7 stress (29 total)