ScenarioNetwork builds home routers (their first card the WAN port) and
their port forwarding (portForwarding, through GatewayFirmware.setStaticNAT).
NatRun plays six stories on nat-home's network and writes the frames, the
calls and the router's NAT table: a ping, a UDP exchange, the same socket
to a second server (whose answer never reaches the LAN: Java keeps one
entry per LAN endpoint, for the first remote only), a TCP connection out,
a forwarded one in, and pings at the WAN address and past it.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>