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

frontend/package.json

@@ -7,6 +7,7 @@
     "dev": "webpack serve --mode development --open",
     "build": "webpack --mode production",
     "lint": "eslint src --ext .js,.jsx,.ts,.tsx",
+    "check": "tsc --noEmit && npm run lint",
     "test:engine": "node --test tests/workspaceEngine.test.js"
   },
   "dependencies": {

frontend/src/documents/DocumentSummarySection.tsx

@@ -12,7 +12,7 @@ import {
   toIssuedTimestamp,
 } from '../utils/date';
 import { describeDocumentSummary, type DocumentSummaryRow } from './documentSummary';
-import { isPlainObject } from '../utils/typeGuards';
+
 import { useFolderManager } from '../folders/FolderManagerContext';
 
 type Identifier = string | number;
@@ -128,11 +128,11 @@ const resolveOptionName = (source?: QuickAddOption | string | null): string => {
   if (!source) {
     return '';
   }
-  if (isPlainObject(source)) {
+  if (typeof source === 'string') {
+    return source.trim();
+  }
   const raw = source.name ?? source.label ?? '';
   return `${raw}`.trim();
-  }
-  return `${source}`.trim();
 };
 
 const normalizeQuickAddOption = (option?: QuickAddOption | string | null): QuickAddEntry | null => {
@@ -140,17 +140,17 @@ const normalizeQuickAddOption = (option?: QuickAddOption | string | null): Quick
     return null;
   }
   const label = (() => {
-    if (isPlainObject(option)) {
+    if (typeof option === 'string') {
+      return option.trim();
+    }
     const sourceLabel = option.label ?? option.name ?? '';
     return `${sourceLabel}`.trim();
-    }
-    return `${option}`.trim();
   })();
   if (!label) {
     return null;
   }
   return {
-    id: isPlainObject(option) && option.id ? option.id : label,
+    id: typeof option !== 'string' && option.id ? option.id : label,
     label,
     original: option,
   };
@@ -245,7 +245,7 @@ export const TagSection: React.FC<TagSectionProps> = ({
         return;
       }
       if (item.state === 'all' && onRemove) {
-        const payload = isPlainObject(item.payload)
+        const payload = item.payload && typeof item.payload === 'object' && 'id' in item.payload
           ? (item.payload as TagEntry)
           : tags.find((tag) => (tag.id ?? tag.label) === item.id) ?? { id: item.id, label: item.label };
         onRemove(payload);
@@ -379,7 +379,7 @@ export const CorrespondentSection: React.FC<CorrespondentSectionProps> = ({
         return;
       }
       if (item.state === 'all' && onRemove) {
-        const payload = isPlainObject(item.payload)
+        const payload = item.payload && typeof item.payload === 'object' && 'id' in item.payload
           ? (item.payload as CorrespondentEntry)
           : entries.find((entry) => (entry.id ?? entry.name) === item.id) ?? { id: item.id, name: item.label };
         onRemove(payload);
@@ -393,7 +393,7 @@ export const CorrespondentSection: React.FC<CorrespondentSectionProps> = ({
       if (!resolvedName) {
         return;
       }
-      const payload = isPlainObject(source)
+      const payload = typeof source !== 'string'
         ? { ...source, name: resolvedName }
         : { id: null, name: resolvedName };
       onAdd({ name: resolvedName, option: payload, input: null });
@@ -518,7 +518,7 @@ const DocumentSummarySection: React.FC<DocumentSummarySectionProps> = ({
         if (active) {
           setFolderName(name);
         }
-      }).catch(() => {});
+      }).catch(() => { });
     }
     return () => {
       active = false;

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 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);

frontend/src/settings/components/CapabilityDropdown.tsx

@@ -7,7 +7,7 @@ import {
 } from 'react';
 import type { JSX } from 'react';
 import { CheckIcon, ChevronDownIcon } from '../../ui/icons';
-import { isPlainObject } from '../../utils/typeGuards';
+
 
 type CapabilityValue = string | number;
 
@@ -29,9 +29,7 @@ interface CapabilityDropdownProps {
   summaryLabel?: string;
 }
 
-const isCapabilityOption = (
+
-  option: CapabilityDropdownOption | CapabilityValue | null,
-): option is CapabilityDropdownOption => isPlainObject(option);
 
 const resolveCapabilityValue = (
   option: CapabilityDropdownOption | CapabilityValue | null,
@@ -39,8 +37,8 @@ const resolveCapabilityValue = (
   if (option == null) {
     return null;
   }
-  if (!isCapabilityOption(option)) {
+  if (typeof option !== 'object') {
-    return option as CapabilityValue;
+    return option;
   }
   if (option.value != null) {
     return option.value;
@@ -170,7 +168,7 @@ const CapabilityDropdown = ({
               }
               const label = formatLabel
                 ? formatLabel(value)
-                : (isCapabilityOption(option) && option?.label) || String(value);
+                : (typeof option === 'object' && option?.label) || String(value);
               const selected = selectedValues.includes(value);
               return (
                 <button

frontend/src/settings/sections/CapabilitySetsSection.tsx

@@ -8,7 +8,7 @@ import React, {
 import type { SettingsSectionConfig } from '../SettingsModal';
 import { IconX } from '../../ui/icons';
 import CapabilityDropdown, { CapabilityDropdownOption } from '../components/CapabilityDropdown';
-import { isPlainObject } from '../../utils/typeGuards';
+
 
 type CapabilityValue = string | number;
 type CapabilitySetId = string | number;
@@ -55,15 +55,14 @@ interface CapabilitySetsSectionProps {
 
 type CapabilityOptionInput = CapabilityDropdownOption | CapabilityValue | null;
 
-const isCapabilityOption = (option: CapabilityOptionInput): option is CapabilityDropdownOption =>
+
-  isPlainObject(option);
 
 const resolveCapabilityValue = (option: CapabilityOptionInput): CapabilityValue | null => {
   if (option == null) {
     return null;
   }
-  if (!isCapabilityOption(option)) {
+  if (typeof option === 'string' || typeof option === 'number') {
-    return option as CapabilityValue;
+    return option;
   }
   if (option.value != null) {
     return option.value as CapabilityValue;

frontend/src/ui/QuickAddMenu.tsx

@@ -1,10 +1,10 @@
 import { useCallback, useEffect, useMemo, useRef, useState } from 'react';
 import type { CSSProperties, ReactNode, FormEvent, MutableRefObject } from 'react';
 import { PlusIcon } from './icons';
-import { isPlainObject } from '../utils/typeGuards';
+
 import useFloatingMenu from './useFloatingMenu';
 
-type QuickAddOption = string | number | { id?: string | number; label?: string; name?: string; [key: string]: unknown };
+type QuickAddOption = string | number | { id?: string | number; label?: string; name?: string;[key: string]: unknown };
 
 interface NormalizedOption {
   id?: string | number;
@@ -17,7 +17,7 @@ const normalizeOption = (option: QuickAddOption | null, index: number): Normaliz
   if (option == null) {
     return null;
   }
-  if (isPlainObject(option)) {
+  if (typeof option === 'object') {
     const label = option.label ?? option.name;
     if (label == null) {
       return null;

frontend/src/utils/typeGuards.ts

@@ -1,6 +0,0 @@
-const objectToString = Object.prototype.toString;
-
-export const isPlainObject = (value: unknown): value is Record<string, unknown> =>
-  value !== null && !Array.isArray(value) && Object(value) === value;
-
-