fix: harden merge UI and improve error handling

- MergeAccounts: guard mutationFn against null token/userId
- MergeAccounts: call checkAdminStatus after successful merge
- MergeAccounts: add fallback when success but tokens null
- MergeAccounts: fix ErrorState showing "expired" for all errors
- MergeAccounts: fix formatCountdown dead ternary and hardcoded English
- MergeAccounts: add staleTime/refetchOnWindowFocus to preview query
- MergeAccounts: remove manual useCallback (React Compiler handles it)
- LinkOAuthCallback: add toast feedback on all error/success paths
- ConnectedAccounts: use invalidateQueries instead of refetch
- ConnectedAccounts: add error state rendering
- ConnectedAccounts/LinkOAuthCallback: share sessionStorage key constants
- i18n: add missing profile.accounts.linking key to zh and fa locales

src/locales/fa.json

@@ -3049,6 +3049,7 @@
       "linkError": "اتصال حساب ناموفق بود",
       "unlinkError": "قطع اتصال ناموفق بود",
       "goToAccounts": "حساب‌های متصل",
+      "linking": "در حال اتصال حساب...",
       "providers": {
         "telegram": "تلگرام",
         "email": "ایمیل",

src/locales/zh.json

@@ -3048,6 +3048,7 @@
       "linkError": "关联账户失败",
       "unlinkError": "取消关联失败",
       "goToAccounts": "关联账户",
+      "linking": "正在关联账户...",
       "providers": {
         "telegram": "Telegram",
         "email": "邮箱",

src/pages/ConnectedAccounts.tsx

@@ -1,5 +1,5 @@
 import { useTranslation } from 'react-i18next';
-import { useQuery, useMutation } from '@tanstack/react-query';
+import { useQuery, useMutation, useQueryClient } from '@tanstack/react-query';
 import { motion } from 'framer-motion';
 import { authApi } from '../api/auth';
 import { useToast } from '../components/Toast';
@@ -7,6 +7,7 @@ import { Card } from '@/components/data-display/Card';
 import { Button } from '@/components/primitives/Button';
 import { staggerContainer, staggerItem } from '@/components/motion/transitions';
 import OAuthProviderIcon from '../components/OAuthProviderIcon';
+import { LINK_OAUTH_STATE_KEY, LINK_OAUTH_PROVIDER_KEY } from './LinkOAuthCallback';
 import type { LinkedProvider } from '../types';
 
 const OAUTH_PROVIDERS = ['google', 'yandex', 'discord', 'vk'];
@@ -78,8 +79,9 @@ function LoadingSkeleton() {
 export default function ConnectedAccounts() {
   const { t } = useTranslation();
   const { showToast } = useToast();
+  const queryClient = useQueryClient();
 
-  const { data, isLoading, refetch } = useQuery({
+  const { data, isLoading, isError } = useQuery({
     queryKey: ['linked-providers'],
     queryFn: () => authApi.getLinkedProviders(),
   });
@@ -87,7 +89,7 @@ export default function ConnectedAccounts() {
   const unlinkMutation = useMutation({
     mutationFn: (provider: string) => authApi.unlinkProvider(provider),
     onSuccess: () => {
-      refetch();
+      queryClient.invalidateQueries({ queryKey: ['linked-providers'] });
       showToast({
         type: 'success',
         message: t('profile.accounts.unlinkSuccess'),
@@ -111,8 +113,8 @@ export default function ConnectedAccounts() {
   const handleLink = async (provider: string) => {
     try {
       const { authorize_url, state } = await authApi.linkProviderInit(provider);
-      sessionStorage.setItem('link_oauth_state', state);
-      sessionStorage.setItem('link_oauth_provider', provider);
+      sessionStorage.setItem(LINK_OAUTH_STATE_KEY, state);
+      sessionStorage.setItem(LINK_OAUTH_PROVIDER_KEY, provider);
       window.location.href = authorize_url;
     } catch {
       showToast({
@@ -150,6 +152,15 @@ export default function ConnectedAccounts() {
         </motion.div>
       )}
 
+      {/* Error state */}
+      {isError && (
+        <motion.div variants={staggerItem}>
+          <Card>
+            <p className="text-center text-dark-400">{t('common.error')}</p>
+          </Card>
+        </motion.div>
+      )}
+
       {/* Provider cards */}
       {data?.providers.map((provider) => (
         <motion.div key={provider.provider} variants={staggerItem}>

src/pages/LinkOAuthCallback.tsx

@@ -2,10 +2,11 @@ import { useEffect, useRef } from 'react';
 import { useNavigate, useSearchParams } from 'react-router';
 import { useTranslation } from 'react-i18next';
 import { authApi } from '../api/auth';
+import { useToast } from '../components/Toast';
 
-// SessionStorage keys (set by ConnectedAccounts.tsx handleLink)
-const LINK_OAUTH_STATE_KEY = 'link_oauth_state';
-const LINK_OAUTH_PROVIDER_KEY = 'link_oauth_provider';
+// SessionStorage keys — shared with ConnectedAccounts.tsx
+export const LINK_OAUTH_STATE_KEY = 'link_oauth_state';
+export const LINK_OAUTH_PROVIDER_KEY = 'link_oauth_provider';
 
 function getAndClearLinkOAuthState(): { state: string; provider: string } | null {
   const state = sessionStorage.getItem(LINK_OAUTH_STATE_KEY);
@@ -20,6 +21,7 @@ export default function LinkOAuthCallback() {
   const { t } = useTranslation();
   const navigate = useNavigate();
   const [searchParams] = useSearchParams();
+  const { showToast } = useToast();
   const hasRun = useRef(false);
 
   useEffect(() => {
@@ -34,6 +36,7 @@ export default function LinkOAuthCallback() {
       const deviceId = searchParams.get('device_id');
 
       if (!code || !urlState) {
+        showToast({ type: 'error', message: t('profile.accounts.linkError') });
         navigate('/profile/accounts', { replace: true });
         return;
       }
@@ -41,12 +44,14 @@ export default function LinkOAuthCallback() {
       // Get saved state from sessionStorage
       const saved = getAndClearLinkOAuthState();
       if (!saved) {
+        showToast({ type: 'error', message: t('profile.accounts.linkError') });
         navigate('/profile/accounts', { replace: true });
         return;
       }
 
       // Validate state match
       if (saved.state !== urlState) {
+        showToast({ type: 'error', message: t('profile.accounts.linkError') });
         navigate('/profile/accounts', { replace: true });
         return;
       }
@@ -64,15 +69,17 @@ export default function LinkOAuthCallback() {
           navigate(`/merge/${response.merge_token}`, { replace: true });
         } else {
           // Success - redirect back to accounts
+          showToast({ type: 'success', message: t('profile.accounts.linkSuccess') });
           navigate('/profile/accounts', { replace: true });
         }
       } catch {
+        showToast({ type: 'error', message: t('profile.accounts.linkError') });
         navigate('/profile/accounts', { replace: true });
       }
     };
 
     linkAccount();
-  }, [searchParams, navigate]);
+  }, [searchParams, navigate, showToast, t]);
 
   return (
     <div className="flex min-h-screen items-center justify-center">

src/pages/MergeAccounts.tsx

@@ -1,4 +1,4 @@
-import { useState, useEffect, useCallback } from 'react';
+import { useState, useEffect } from 'react';
 import { useParams, useNavigate, Link } from 'react-router';
 import { useTranslation } from 'react-i18next';
 import { useQuery, useMutation } from '@tanstack/react-query';
@@ -114,10 +114,7 @@ function ProviderBadgeIcon({ provider }: { provider: string }) {
 function formatCountdown(seconds: number): string {
   const min = Math.floor(seconds / 60);
   const sec = seconds % 60;
-  if (min > 0) {
-    return `${min} ${min === 1 ? 'min' : 'min'} ${sec.toString().padStart(2, '0')} ${sec === 1 ? 'sec' : 'sec'}`;
-  }
-  return `${sec} sec`;
+  return `${min}:${sec.toString().padStart(2, '0')}`;
 }
 
 function formatDate(dateStr: string | null): string {
@@ -329,7 +326,7 @@ function ErrorState() {
       </motion.div>
 
       <motion.div variants={staggerItem} className="text-center">
-        <p className="text-lg font-medium text-dark-100">{t('merge.expired')}</p>
+        <p className="text-lg font-medium text-dark-100">{t('merge.error')}</p>
       </motion.div>
 
       <motion.div variants={staggerItem}>
@@ -362,6 +359,8 @@ export default function MergeAccounts() {
     queryFn: () => authApi.getMergePreview(mergeToken!),
     enabled: !!mergeToken,
     retry: false,
+    staleTime: Infinity,
+    refetchOnWindowFocus: false,
   });
 
   // Auto-select subscription when data loads
@@ -403,14 +402,26 @@ export default function MergeAccounts() {
 
   // Execute merge
   const mergeMutation = useMutation({
-    mutationFn: () => authApi.executeMerge(mergeToken!, selectedUserId!),
-    onSuccess: (response) => {
+    mutationFn: () => {
+      if (!mergeToken || !selectedUserId) {
+        return Promise.reject(new Error('Missing merge token or user selection'));
+      }
+      return authApi.executeMerge(mergeToken, selectedUserId);
+    },
+    onSuccess: async (response) => {
       if (response.success && response.access_token && response.refresh_token) {
-        const { setTokens, setUser } = useAuthStore.getState();
+        const { setTokens, setUser, checkAdminStatus } = useAuthStore.getState();
         setTokens(response.access_token, response.refresh_token);
         if (response.user) {
           setUser(response.user);
         }
+        await checkAdminStatus();
+        showToast({
+          type: 'success',
+          message: t('merge.success'),
+        });
+        navigate('/', { replace: true });
+      } else {
         showToast({
           type: 'success',
           message: t('merge.success'),
@@ -426,14 +437,14 @@ export default function MergeAccounts() {
     },
   });
 
-  const handleMerge = useCallback(() => {
+  const handleMerge = () => {
     if (!selectedUserId || mergeMutation.isPending || isExpired) return;
     mergeMutation.mutate();
-  }, [selectedUserId, mergeMutation, isExpired]);
+  };
 
-  const handleCancel = useCallback(() => {
+  const handleCancel = () => {
     navigate('/profile/accounts', { replace: true });
-  }, [navigate]);
+  };
 
   // Derived state
   const bothHaveSubscriptions =