fix(windows): protect existing lifecycle child first

tools/tht/internal/lifecycle/lock.go

@@ -50,14 +50,31 @@ type Transaction struct {
 // Acquire obtains the shared lock used by backup, restore, Pi lifecycle and product updates.
 func Acquire(installation config.Installation) (*Lock, error) {
 	directory := installation.ControlDirectory()
-	// The lifecycle directory is also the restore staging parent. Protect both the shared
-	// .tht directory and this installation's child before any lock or staging artifact is
-	// created; chmod alone does not install an owner-only DACL on Windows.
-	if err := ensurePrivateLifecycleDirectory(filepath.Dir(directory)); err != nil {
-		return nil, fmt.Errorf("protect lifecycle control parent: %w", err)
-	}
-	if err := ensurePrivateLifecycleDirectory(directory); err != nil {
-		return nil, fmt.Errorf("protect lifecycle control directory: %w", err)
+	parent := filepath.Dir(directory)
+	// The lifecycle directory is also the restore staging parent. An existing Windows child
+	// must be protected before its parent: replacing the parent's inheritable ACL first can
+	// remove the child's inherited owner authority before the child receives its protected DACL.
+	// For a new installation the parent must instead exist before safe child creation.
+	controlInfo, controlErr := os.Lstat(directory)
+	if controlErr == nil {
+		if !controlInfo.IsDir() || controlInfo.Mode()&os.ModeSymlink != 0 {
+			return nil, errors.New("lifecycle control directory is not a regular directory")
+		}
+		if err := ensurePrivateLifecycleDirectory(directory); err != nil {
+			return nil, fmt.Errorf("protect lifecycle control directory: %w", err)
+		}
+		if err := ensurePrivateLifecycleDirectory(parent); err != nil {
+			return nil, fmt.Errorf("protect lifecycle control parent: %w", err)
+		}
+	} else if errors.Is(controlErr, os.ErrNotExist) {
+		if err := ensurePrivateLifecycleDirectory(parent); err != nil {
+			return nil, fmt.Errorf("protect lifecycle control parent: %w", err)
+		}
+		if err := ensurePrivateLifecycleDirectory(directory); err != nil {
+			return nil, fmt.Errorf("protect lifecycle control directory: %w", err)
+		}
+	} else {
+		return nil, errors.New("lifecycle control directory is unavailable")
 	}
 	info, err := os.Lstat(directory)
 	if err != nil || !info.IsDir() || info.Mode()&os.ModeSymlink != 0 {