diff --git a/frontend/src/hooks/documents/useDocumentDragHandlers.ts b/frontend/src/hooks/documents/useDocumentDragHandlers.ts
index 12c0591..1ff8d28 100644
--- a/frontend/src/hooks/documents/useDocumentDragHandlers.ts
+++ b/frontend/src/hooks/documents/useDocumentDragHandlers.ts
@@ -1,9 +1,9 @@
-import { useCallback, useEffect, useRef } from 'react';
+import { useCallback, useEffect, useMemo, useRef } from 'react';
 import type { DragEvent } from 'react';
-import { isPlainObject } from '../../utils/typeGuards';
 
 type Identifier = string | number;
-type FolderIdentifier = Identifier | 'root';
+type FolderIdentifier = string | 'root';
+type FolderInput = FolderIdentifier | number;
 
 interface DocumentLike {
   id?: Identifier | null;
@@ -24,7 +24,7 @@ type HandleEntrySelectionFn = (
 interface UseDocumentDragHandlersOptions {
   selectedEntries: string[];
   selectedDocumentIds: Identifier[];
-  selectedFolderIds: FolderIdentifier[];
+  selectedFolderIds: FolderInput[];
   applySelection: ApplySelectionFn;
   handleEntrySelection: HandleEntrySelectionFn;
   documentLookup: Map<Identifier, DocumentLike>;
@@ -49,6 +49,10 @@ const useDocumentDragHandlers = ({
   documentsViewMode,
 }: UseDocumentDragHandlersOptions) => {
   const dragPreviewRef = useRef<HTMLDivElement | null>(null);
+  const normalizedFolderIds = useMemo(
+    () => selectedFolderIds.map((id) => (id === 'root' ? 'root' : String(id))) as FolderIdentifier[],
+    [selectedFolderIds],
+  );
 
   const destroyDragPreview = useCallback(() => {
     const node = dragPreviewRef.current;
@@ -61,7 +65,7 @@ const useDocumentDragHandlers = ({
   useEffect(() => destroyDragPreview, [destroyDragPreview]);
 
   const createDragPreview = useCallback(
-    ({ documents = [], folders = [] }: { documents?: DocumentLike[]; folders?: Array<FolderIdentifier | Identifier> } = {}) => {
+    ({ documents = [], folders = [] }: { documents?: DocumentLike[]; folders?: FolderIdentifier[] } = {}) => {
       destroyDragPreview();
 
       const docEntries = (documents || []).filter(Boolean);
@@ -145,17 +149,7 @@ const useDocumentDragHandlers = ({
           }
         } else {
           const payload = item.payload;
-          const folderId = (() => {
-            if (isPlainObject(payload) && 'id' in payload) {
-              return (payload as { id?: FolderIdentifier }).id ?? null;
-            }
-            const maybeTrim = (payload as { trim?: () => string })?.trim;
-            if (typeof maybeTrim === 'function') {
-              const nextValue = maybeTrim.call(payload);
-              return nextValue || null;
-            }
-            return null;
-          })();
+          const folderId = payload as FolderIdentifier;
           const rowEl = folderId
             ? (document.getElementById(`folder-row-${folderId}`)
               || document.getElementById(`folder-card-${folderId}`))
@@ -300,28 +294,29 @@ const useDocumentDragHandlers = ({
   );
 
   const handleFolderDragStart = useCallback(
-    (event: DragEvent<HTMLElement>, folderId: FolderIdentifier) => {
-      if (folderId === 'root') {
+    (event: DragEvent<HTMLElement>, folderId: FolderInput) => {
+      const normalizedFolderId: FolderIdentifier = folderId === 'root' ? 'root' : String(folderId);
+      if (normalizedFolderId === 'root') {
         return;
       }
       event.stopPropagation();
-      const folderKey = resolveFolderRowKey(folderId);
+      const folderKey = resolveFolderRowKey(normalizedFolderId);
       const isAlreadySelected = folderKey ? selectedEntries.includes(folderKey) : false;
 
-      let effectiveFolderSelection: FolderIdentifier[] = selectedFolderIds;
+      let effectiveFolderSelection: FolderIdentifier[] = normalizedFolderIds;
       let effectiveDocumentSelection: Identifier[] = selectedDocumentIds;
 
       if (!isAlreadySelected && folderKey) {
-        effectiveFolderSelection = [folderId];
+        effectiveFolderSelection = [normalizedFolderId];
         effectiveDocumentSelection = [];
         handleEntrySelection(folderKey, { preventDefault: () => {} });
       }
 
       const uniqueFolders = effectiveFolderSelection.length
         ? Array.from(new Set(effectiveFolderSelection.filter(Boolean)))
-        : [folderId];
+        : [normalizedFolderId];
 
-      setDraggedFolderId(folderId);
+      setDraggedFolderId(normalizedFolderId);
       if (effectiveDocumentSelection.length) {
         setDraggedDocumentIds(effectiveDocumentSelection);
       }
@@ -360,7 +355,7 @@ const useDocumentDragHandlers = ({
       }
     },
     [
-      selectedFolderIds,
+      normalizedFolderIds,
       selectedEntries,
       selectedDocumentIds,
       handleEntrySelection,