subclasses (ConnectionResetError, BrokenPipeError). When a client
becomes unreachable mid-generation (laptop sleeps, drops off WiFi),
the OS raises OSError: [Errno 113] No route to host (EHOSTUNREACH),
which is a sibling of ConnectionError, not a subclass. It therefore
escaped the handler, propagated through publish_loop, and could crash
the entire server over a single dead client.
