Use %w, not %v, in fmt.Errorf, so errors can be unwrapped.

https://go.dev/blog/go1.13-errors#wrapping-errors-with-w

server/lib/http.go

@@ -147,7 +147,7 @@ func (handler *httpHandler) turbotunnelMode(conn net.Conn, addr net.Addr) error
 	var clientID turbotunnel.ClientID
 	_, err := io.ReadFull(conn, clientID[:])
 	if err != nil {
-		return fmt.Errorf("reading ClientID: %v", err)
+		return fmt.Errorf("reading ClientID: %w", err)
 	}
 
 	// Store a short-term mapping from the ClientID to the client IP