diff --git a/src/web-server/routes/persist-routes.ts b/src/web-server/routes/persist-routes.ts
index 80f1b915..b3e9bbce 100644
--- a/src/web-server/routes/persist-routes.ts
+++ b/src/web-server/routes/persist-routes.ts
@@ -15,6 +15,9 @@ interface BackupFile {
   date: Date;
 }
 
+/** Simple in-memory mutex for restore operations */
+let restoreLock = false;
+
 /** Get Claude settings.json path */
 function getClaudeSettingsPath(): string {
   return path.join(os.homedir(), '.claude', 'settings.json');
@@ -85,6 +88,14 @@ router.get('/backups', (_req: Request, res: Response): void => {
  * Body: { timestamp?: string } - If not provided, restores latest
  */
 router.post('/restore', (req: Request, res: Response): void => {
+  // Check concurrent restore lock
+  if (restoreLock) {
+    res.status(409).json({ error: 'Restore already in progress' });
+    return;
+  }
+
+  restoreLock = true;
+
   try {
     const { timestamp } = req.body;
     const backups = getBackupFiles();
@@ -107,19 +118,6 @@ router.post('/restore', (req: Request, res: Response): void => {
       backup = found;
     }
 
-    // Validate backup JSON
-    try {
-      const content = fs.readFileSync(backup.path, 'utf8');
-      const parsed = JSON.parse(content);
-      if (typeof parsed !== 'object' || parsed === null || Array.isArray(parsed)) {
-        res.status(400).json({ error: 'Backup file is corrupted' });
-        return;
-      }
-    } catch {
-      res.status(400).json({ error: 'Backup file is corrupted or invalid JSON' });
-      return;
-    }
-
     // Security checks
     if (isSymlink(backup.path)) {
       res.status(400).json({ error: 'Backup file is a symlink - refusing for security' });
@@ -132,16 +130,65 @@ router.post('/restore', (req: Request, res: Response): void => {
       return;
     }
 
-    // Restore
-    fs.copyFileSync(backup.path, settingsPath);
+    // Read and validate backup JSON (do this once atomically)
+    let backupContent: string;
+    try {
+      backupContent = fs.readFileSync(backup.path, 'utf8');
+      const parsed = JSON.parse(backupContent);
+      if (typeof parsed !== 'object' || parsed === null || Array.isArray(parsed)) {
+        res.status(400).json({ error: 'Backup file is corrupted' });
+        return;
+      }
+    } catch {
+      res.status(400).json({ error: 'Backup file is corrupted or invalid JSON' });
+      return;
+    }
 
-    res.json({
-      success: true,
-      timestamp: backup.timestamp,
-      date: backup.date.toISOString(),
-    });
+    // Atomic restore with rollback capability
+    const settingsDir = path.dirname(settingsPath);
+    const tempPath = path.join(settingsDir, 'settings.json.restore-tmp');
+    const backupPath = path.join(settingsDir, 'settings.json.rollback-tmp');
+
+    try {
+      // Step 1: Backup current settings for rollback
+      if (fs.existsSync(settingsPath)) {
+        fs.copyFileSync(settingsPath, backupPath);
+      }
+
+      // Step 2: Write validated content to temp file
+      fs.writeFileSync(tempPath, backupContent, 'utf8');
+
+      // Step 3: Atomic rename (replaces existing file)
+      fs.renameSync(tempPath, settingsPath);
+
+      // Step 4: Cleanup rollback backup on success
+      if (fs.existsSync(backupPath)) {
+        fs.unlinkSync(backupPath);
+      }
+
+      res.json({
+        success: true,
+        timestamp: backup.timestamp,
+        date: backup.date.toISOString(),
+      });
+    } catch (error) {
+      // Rollback on failure
+      try {
+        if (fs.existsSync(backupPath)) {
+          fs.renameSync(backupPath, settingsPath);
+        }
+        if (fs.existsSync(tempPath)) {
+          fs.unlinkSync(tempPath);
+        }
+      } catch {
+        // Ignore cleanup errors
+      }
+      throw error;
+    }
   } catch (error) {
     res.status(500).json({ error: (error as Error).message });
+  } finally {
+    restoreLock = false;
   }
 });
 
diff --git a/ui/src/components/cliproxy/provider-editor/account-item.tsx b/ui/src/components/cliproxy/provider-editor/account-item.tsx
index dd4a1989..031a01b3 100644
--- a/ui/src/components/cliproxy/provider-editor/account-item.tsx
+++ b/ui/src/components/cliproxy/provider-editor/account-item.tsx
@@ -41,8 +41,9 @@ import type { AccountItemProps } from './types';
  * Get color class based on quota percentage
  */
 function getQuotaColor(percentage: number): string {
-  if (percentage <= 20) return 'bg-destructive';
-  if (percentage <= 50) return 'bg-yellow-500';
+  const clamped = Math.max(0, Math.min(100, percentage));
+  if (clamped <= 20) return 'bg-destructive';
+  if (clamped <= 50) return 'bg-yellow-500';
   return 'bg-green-500';
 }
 
@@ -257,7 +258,7 @@ export function AccountItem({
                   <TooltipTrigger asChild>
                     <div className="flex items-center gap-2">
                       <Progress
-                        value={minQuota}
+                        value={Math.max(0, Math.min(100, minQuota))}
                         className="h-2 flex-1"
                         indicatorClassName={getQuotaColor(minQuota)}
                       />
diff --git a/ui/src/pages/settings/hooks/use-settings-tab.ts b/ui/src/pages/settings/hooks/use-settings-tab.ts
index 9ec10395..1a4f9192 100644
--- a/ui/src/pages/settings/hooks/use-settings-tab.ts
+++ b/ui/src/pages/settings/hooks/use-settings-tab.ts
@@ -16,7 +16,9 @@ export function useSettingsTab() {
         ? 'proxy'
         : tabParam === 'auth'
           ? 'auth'
-          : 'websearch';
+          : tabParam === 'backups'
+            ? 'backups'
+            : 'websearch';
 
   const setActiveTab = useCallback(
     (tab: SettingsTab) => {
diff --git a/ui/src/pages/settings/index.tsx b/ui/src/pages/settings/index.tsx
index e395db9c..abfd6529 100644
--- a/ui/src/pages/settings/index.tsx
+++ b/ui/src/pages/settings/index.tsx
@@ -3,10 +3,10 @@
  * Main entry point with lazy-loaded sections and URL tab persistence
  */
 
-import { lazy, Suspense, startTransition, useEffect } from 'react';
+import { lazy, Suspense, startTransition, useEffect, Component, type ReactNode } from 'react';
 import { Panel, PanelGroup, PanelResizeHandle } from 'react-resizable-panels';
 import { Button } from '@/components/ui/button';
-import { RefreshCw, FileCode, Copy, Check, GripVertical } from 'lucide-react';
+import { RefreshCw, FileCode, Copy, Check, GripVertical, AlertCircle } from 'lucide-react';
 import { CodeEditor } from '@/components/shared/code-editor';
 import { SettingsProvider } from './context';
 import { useSettingsTab, useRawConfig } from './hooks';
@@ -21,6 +21,45 @@ const ProxySection = lazy(() => import('./sections/proxy'));
 const AuthSection = lazy(() => import('./sections/auth-section'));
 const BackupsSection = lazy(() => import('./sections/backups-section'));
 
+// Error Boundary for lazy-loaded sections
+class SectionErrorBoundary extends Component<
+  { children: ReactNode },
+  { hasError: boolean; error: Error | null }
+> {
+  constructor(props: { children: ReactNode }) {
+    super(props);
+    this.state = { hasError: false, error: null };
+  }
+
+  static getDerivedStateFromError(error: Error) {
+    return { hasError: true, error };
+  }
+
+  render() {
+    if (this.state.hasError) {
+      return (
+        <div className="flex-1 flex items-center justify-center text-muted-foreground">
+          <div className="text-center p-6 max-w-md">
+            <AlertCircle className="w-12 h-12 mx-auto mb-4 text-destructive" />
+            <p className="font-medium text-foreground mb-2">Failed to load section</p>
+            <p className="text-sm mb-4">{this.state.error?.message || 'Unknown error occurred'}</p>
+            <Button
+              variant="outline"
+              onClick={() => window.location.reload()}
+              className="inline-flex items-center gap-2"
+            >
+              <RefreshCw className="w-4 h-4" />
+              Reload page
+            </Button>
+          </div>
+        </div>
+      );
+    }
+
+    return this.props.children;
+  }
+}
+
 // Inner component that uses context
 function SettingsPageInner() {
   const { activeTab, setActiveTab } = useSettingsTab();
@@ -55,13 +94,15 @@ function SettingsPageInner() {
             </div>
 
             {/* Tab Content */}
-            <Suspense fallback={<SectionSkeleton />}>
-              {activeTab === 'websearch' && <WebSearchSection />}
-              {activeTab === 'globalenv' && <GlobalEnvSection />}
-              {activeTab === 'proxy' && <ProxySection />}
-              {activeTab === 'auth' && <AuthSection />}
-              {activeTab === 'backups' && <BackupsSection />}
-            </Suspense>
+            <SectionErrorBoundary>
+              <Suspense fallback={<SectionSkeleton />}>
+                {activeTab === 'websearch' && <WebSearchSection />}
+                {activeTab === 'globalenv' && <GlobalEnvSection />}
+                {activeTab === 'proxy' && <ProxySection />}
+                {activeTab === 'auth' && <AuthSection />}
+                {activeTab === 'backups' && <BackupsSection />}
+              </Suspense>
+            </SectionErrorBoundary>
           </div>
         </Panel>
 
diff --git a/ui/src/pages/settings/sections/backups-section.tsx b/ui/src/pages/settings/sections/backups-section.tsx
index 8d0ee98e..3a9985a7 100644
--- a/ui/src/pages/settings/sections/backups-section.tsx
+++ b/ui/src/pages/settings/sections/backups-section.tsx
@@ -3,7 +3,7 @@
  * Settings section for managing config.yaml backups (list and restore)
  */
 
-import { useEffect, useState, useCallback } from 'react';
+import { useEffect, useState, useCallback, useRef } from 'react';
 import { Button } from '@/components/ui/button';
 import { Alert, AlertDescription } from '@/components/ui/alert';
 import { ScrollArea } from '@/components/ui/scroll-area';
@@ -25,6 +25,10 @@ interface BackupsResponse {
 export default function BackupsSection() {
   const { fetchRawConfig } = useRawConfig();
 
+  // AbortController refs for cleanup
+  const abortControllerRef = useRef<AbortController | null>(null);
+  const restoreAbortControllerRef = useRef<AbortController | null>(null);
+
   // State
   const [backups, setBackups] = useState<Backup[]>([]);
   const [loading, setLoading] = useState(true);
@@ -34,16 +38,24 @@ export default function BackupsSection() {
 
   // Fetch backups
   const fetchBackups = useCallback(async () => {
+    // Abort previous request
+    abortControllerRef.current?.abort();
+    abortControllerRef.current = new AbortController();
+
     try {
       setLoading(true);
       setError(null);
-      const response = await fetch('/api/persist/backups');
+      const response = await fetch('/api/persist/backups', {
+        signal: abortControllerRef.current.signal,
+      });
       if (!response.ok) {
         throw new Error('Failed to fetch backups');
       }
       const data: BackupsResponse = await response.json();
       setBackups(data.backups || []);
     } catch (err) {
+      // Ignore abort errors
+      if (err instanceof Error && err.name === 'AbortError') return;
       setError(err instanceof Error ? err.message : 'Unknown error');
     } finally {
       setLoading(false);
@@ -52,6 +64,10 @@ export default function BackupsSection() {
 
   // Restore backup
   const restoreBackup = async (timestamp: string) => {
+    // Abort previous restore request
+    restoreAbortControllerRef.current?.abort();
+    restoreAbortControllerRef.current = new AbortController();
+
     try {
       setRestoring(timestamp);
       setError(null);
@@ -59,6 +75,7 @@ export default function BackupsSection() {
         method: 'POST',
         headers: { 'Content-Type': 'application/json' },
         body: JSON.stringify({ timestamp }),
+        signal: restoreAbortControllerRef.current.signal,
       });
 
       if (!response.ok) {
@@ -70,6 +87,8 @@ export default function BackupsSection() {
       await fetchBackups();
       await fetchRawConfig();
     } catch (err) {
+      // Ignore abort errors
+      if (err instanceof Error && err.name === 'AbortError') return;
       setError(err instanceof Error ? err.message : 'Unknown error');
     } finally {
       setRestoring(null);
@@ -81,6 +100,14 @@ export default function BackupsSection() {
     fetchBackups();
   }, [fetchBackups]);
 
+  // Cleanup: abort pending requests on unmount
+  useEffect(() => {
+    return () => {
+      abortControllerRef.current?.abort();
+      restoreAbortControllerRef.current?.abort();
+    };
+  }, []);
+
   // Clear success after timeout
   useEffect(() => {
     if (success) {
diff --git a/ui/src/pages/settings/sections/proxy/index.tsx b/ui/src/pages/settings/sections/proxy/index.tsx
index 274ba607..ab9d8ef5 100644
--- a/ui/src/pages/settings/sections/proxy/index.tsx
+++ b/ui/src/pages/settings/sections/proxy/index.tsx
@@ -60,6 +60,13 @@ export default function ProxySection() {
     }
   };
 
+  // Log when debug mode changes
+  useEffect(() => {
+    if (debugMode) {
+      console.log('[CCS Debug] Debug mode enabled - proxy config:', config);
+    }
+  }, [debugMode, config]);
+
   // Load data on mount
   useEffect(() => {
     fetchConfig();
@@ -302,7 +309,7 @@ export default function ProxySection() {
                 <div>
                   <p className="font-medium text-sm">Debug Mode</p>
                   <p className="text-xs text-muted-foreground">
-                    Show verbose logging and diagnostic info (--verbose)
+                    Enable developer diagnostics in browser console
                   </p>
                 </div>
                 <Switch