refactor: Delete isPlainObject type guard and replace its usages with direct typeof checks.

frontend/src/hooks/documents/useDocumentCorrespondentActions.ts

@@ -1,5 +1,5 @@
 import { useCallback, useMemo } from 'react';
-import { isPlainObject } from '../../utils/typeGuards';
+
 
 type ApiClient = {
   post: (path: string, body?: unknown) => Promise<{ data: unknown }>;
@@ -124,16 +124,14 @@ const useDocumentCorrespondentActions = ({
     if (!option) {
       return null;
     }
-    if (isPlainObject(option) && 'id' in option) {
-      return option as CorrespondentOption;
-    }
     if (typeof option === 'string') {
       const trimmed = option.trim();
       if (trimmed) {
         return { id: null, name: trimmed };
       }
+      return null;
     }
-    return null;
+    return option;
   };
 
   const handleCorrespondentAdd = useCallback(

frontend/src/hooks/documents/useDocumentMutations.ts

@@ -1,5 +1,5 @@
 import { useCallback } from 'react';
-import { isPlainObject } from '../../utils/typeGuards';
+
 import type { Dispatch, MutableRefObject, SetStateAction } from 'react';
 import { DEFAULT_FOLDER_NAME, getRowId, isDocumentRowKey } from '../../app/appLayoutUtils';
 import {
@@ -66,7 +66,7 @@ interface DocumentLike {
 
 interface FolderContents {
   documents?: DocumentLike[];
-  subfolders?: Array<{ id?: FolderId; [key: string]: unknown }>;
+  subfolders?: Array<{ id?: FolderId;[key: string]: unknown }>;
   [key: string]: unknown;
 }
 
@@ -175,7 +175,7 @@ interface UseDocumentMutationsResult {
 
 const normalizeDocumentId = (value: unknown): DocumentId | null => {
   if (!value) return null;
-  if (isPlainObject(value) && 'id' in value && value.id != null) {
+  if (value && typeof value === 'object' && 'id' in value && value.id != null) {
     return value.id as DocumentId;
   }
   return value as DocumentId;
@@ -446,7 +446,7 @@ const useDocumentMutations = ({
     },
     [
       token,
-      documentLookup,
+
       removeDocumentsFromCaches,
       previewDocumentId,
       closeDocumentPreview,
@@ -495,7 +495,8 @@ const useDocumentMutations = ({
   );
 
   const handleDocumentIssuedUpdate = useCallback(
-    async (documentId: DocumentId, nextIssuedDate: number | null) => {const payload = { issued_at: nextIssuedDate || null };
+    async (documentId: DocumentId, nextIssuedDate: number | null) => {
+      const payload = { issued_at: nextIssuedDate || null };
       try {
         const data = await updateDocument(documentId, payload);
         const updatedDocument = extractDocumentFromResponse?.(data);