//! A minimal ExecSandbox guest: bridges an external connection back to
//! itself, writing back whatever data it receives on one. Run it with a
//! host launched as `execsandbox -l <address> ...`.
//!
//! Sandbox-to-sandbox messages and connection lifecycle events
//! (ConnEstablished, ConnClosed) are received but ignored, per spec
//! section 5.3's guidance to skip message kinds a guest doesn't act on
//! rather than treating them as errors.
use Kind;