Function ServeLocal 

pub async fn ServeLocal(
    Port: u16,
    Secret: SharedSecret,
    Registry: Arc<HandlerRegistry>,
) -> Result<()>

Run a WebSocket server on 127.0.0.1:<port>. Loops forever accepting connections; spawns a task per connection.

Returns Err only on bind failure; per-connection errors are logged but never propagated (single bad client must not kill the listener).