connectedSocketFD _handle.fd

Trap: Node’s private socket._handle.fd looks usable because host Node exposes the connected Unix descriptor, but it is undocumented and host-runtime tests do not prove behavior or inheritance in the shipped SEA. Fix: fail closed unless it is a nonnegative socket fd, then run descriptor, SO_PEERCRED, peer-PID, unrelated-child inheritance, and same-UID delegation acceptance against the exact Node 26.4 SEA; Node 24 evidence never satisfies this gate.