fix: only chown when both UID and GID are set (archive mode)

Author: rgarcia

lib/system/guest_agent/main.go

@@ -424,7 +424,9 @@ func (s *guestServer) CopyToGuest(stream pb.GuestService_CopyToGuestServer) erro
 	}
 
 	// Set ownership if provided (archive mode)
-	if start.Uid > 0 || start.Gid > 0 {
+	// Only chown when both UID and GID are explicitly set (non-zero)
+	// to avoid accidentally setting one to root (0) when only the other is specified
+	if start.Uid > 0 && start.Gid > 0 {
 		if err := os.Chown(start.Path, int(start.Uid), int(start.Gid)); err != nil {
 			log.Printf("[guest-agent] warning: failed to set ownership on %s: %v", start.Path, err)
 		}