fix: align WebDAV overwrite authorization

chfs-ng/internal/api/server.go

@@ -1061,12 +1061,13 @@ func (f *webdavStorageFS) Copy(ctx context.Context, name, dest string, opts *web
 	if sameOrDescendantPath(src, dst) {
 		return false, webdav.NewHTTPError(http.StatusConflict, fmt.Errorf("destination is inside source"))
 	}
-	if opts != nil && opts.NoOverwrite {
-		if _, err := f.store.Stat(dst); err == nil {
-			return false, webdav.NewHTTPError(http.StatusPreconditionFailed, fmt.Errorf("destination exists"))
-		} else if !os.IsNotExist(err) {
-			return false, err
-		}
+	_, dstErr := f.store.Stat(dst)
+	dstExists := dstErr == nil
+	if dstErr != nil && !os.IsNotExist(dstErr) {
+		return false, dstErr
+	}
+	if opts != nil && opts.NoOverwrite && dstExists {
+		return false, webdav.NewHTTPError(http.StatusPreconditionFailed, fmt.Errorf("destination exists"))
 	}
 	if m, ok := f.store.(storage.Multi); ok {
 		srcRoot, _, srcOK := m.FindRoot(src)
@@ -1094,7 +1095,7 @@ func (f *webdavStorageFS) Copy(ctx context.Context, name, dest string, opts *web
 			}
 			_ = created
 		}
-		return true, nil
+		return !dstExists, nil
 	}
 	in, err := f.store.Open(src)
 	if err != nil {
@@ -1114,7 +1115,7 @@ func (f *webdavStorageFS) Copy(ctx context.Context, name, dest string, opts *web
 	if closeErr != nil {
 		return false, closeErr
 	}
-	return true, nil
+	return !dstExists, nil
 }
 
 func (f *webdavStorageFS) Move(ctx context.Context, name, dest string, opts *webdav.MoveOptions) (bool, error) {
@@ -1129,12 +1130,12 @@ func (f *webdavStorageFS) Move(ctx context.Context, name, dest string, opts *web
 	if sameOrDescendantPath(src, dst) {
 		return false, webdav.NewHTTPError(http.StatusConflict, fmt.Errorf("destination is inside source"))
 	}
-	if opts == nil || opts.NoOverwrite {
-		if _, err := f.store.Stat(dst); err == nil {
-			return false, webdav.NewHTTPError(http.StatusPreconditionFailed, fmt.Errorf("destination exists"))
-		} else if !os.IsNotExist(err) {
-			return false, err
-		}
+	if _, err := f.store.Stat(dst); err == nil {
+		// CHFS v4 MOVE does not overwrite an existing destination, even when
+		// Overwrite is omitted/T and the caller has delete permission.
+		return false, webdav.NewHTTPError(http.StatusPreconditionFailed, fmt.Errorf("destination exists"))
+	} else if !os.IsNotExist(err) {
+		return false, err
 	}
 	if m, ok := f.store.(storage.Multi); ok {
 		srcRoot, _, srcOK := m.FindRoot(src)
@@ -1370,6 +1371,15 @@ func (f *webdavAuthFS) Create(ctx context.Context, name string, body io.ReadClos
 	if err := f.allow(parent, auth.Write); err != nil {
 		return nil, false, err
 	}
+	// CHFS permits PUT to overwrite an existing file only when the target
+	// itself is writable. A writable parent alone is enough for creation.
+	if _, err := f.inner.Stat(ctx, name); err == nil {
+		if err := f.allow(name, auth.Write); err != nil {
+			return nil, false, err
+		}
+	} else if !os.IsNotExist(err) {
+		return nil, false, err
+	}
 	return f.inner.Create(ctx, name, body, opts)
 }
 func (f *webdavAuthFS) RemoveAll(ctx context.Context, name string, opts *webdav.RemoveAllOptions) error {