fix: use bufio reader instead of raw conn in vsock proxy bidirectional copy

In handleVsockConnection, the handshake is read using a bufio.NewReader(conn),
but the bidirectional proxy was using io.Copy(guestConn, conn) which reads from
the raw conn. Any data buffered by the bufio.Reader beyond the handshake line
would be silently lost. Use the buffered reader instead, consistent with the
client-side implementations in vsock.go that use bufferedConn wrappers.

Author: cursoragent

cmd/vz-shim/server.go

@@ -246,7 +246,7 @@ func (s *ShimServer) handleVsockConnection(conn net.Conn) {
 	done := make(chan struct{}, 2)
 
 	go func() {
-		io.Copy(guestConn, conn)
+		io.Copy(guestConn, reader)
 		done <- struct{}{}
 	}()