diff --git a/ui/src/components/account/add-account-dialog.tsx b/ui/src/components/account/add-account-dialog.tsx
index e426c0df..6dd6dba7 100644
--- a/ui/src/components/account/add-account-dialog.tsx
+++ b/ui/src/components/account/add-account-dialog.tsx
@@ -7,7 +7,7 @@
  * For Kiro: Also shows "Import from IDE" option.
  */
 
-import { useState, useEffect, useRef } from 'react';
+import { useState, useEffect, useRef, useCallback } from 'react';
 import {
   Dialog,
   DialogContent,
@@ -88,6 +88,15 @@ export function AddAccountDialog({
   const nicknameTrimmed = nickname.trim();
   const errorMessage = localError || authFlow.error;
 
+  const fetchAgyBypassState = useCallback(async (): Promise<boolean> => {
+    const response = await fetch('/api/settings/auth/antigravity-risk');
+    if (!response.ok) {
+      throw new Error('Failed to load Antigravity power user setting');
+    }
+    const data = (await response.json()) as { antigravityAckBypass?: boolean };
+    return data.antigravityAckBypass === true;
+  }, []);
+
   const resetAndClose = () => {
     setNickname('');
     setCallbackUrl('');
@@ -122,13 +131,9 @@ export function AddAccountDialog({
     const loadAgyBypassState = async () => {
       try {
         setAgyAckBypassLoading(true);
-        const response = await fetch('/api/settings/auth/antigravity-risk');
-        if (!response.ok) {
-          throw new Error('Failed to load Antigravity power user setting');
-        }
-        const data = (await response.json()) as { antigravityAckBypass?: boolean };
+        const enabled = await fetchAgyBypassState();
         if (!cancelled) {
-          setAgyAckBypassEnabled(data.antigravityAckBypass === true);
+          setAgyAckBypassEnabled(enabled);
         }
       } catch {
         if (!cancelled) {
@@ -146,7 +151,48 @@ export function AddAccountDialog({
     return () => {
       cancelled = true;
     };
-  }, [open, provider]);
+  }, [fetchAgyBypassState, open, provider]);
+
+  useEffect(() => {
+    if (!open || provider !== 'agy' || !authFlow.error || !agyAckBypassEnabled) {
+      return;
+    }
+
+    const normalizedError = authFlow.error.toLowerCase();
+    const ackRequired =
+      normalizedError.includes('agy_risk_ack_required') ||
+      normalizedError.includes('responsibility acknowledgement') ||
+      normalizedError.includes('responsibility checklist');
+    if (!ackRequired) return;
+
+    let cancelled = false;
+
+    const syncBypassState = async () => {
+      try {
+        setAgyAckBypassLoading(true);
+        const enabled = await fetchAgyBypassState();
+        if (cancelled) return;
+        setAgyAckBypassEnabled(enabled);
+        if (!enabled) {
+          setLocalError('Power user mode is off. Complete the AGY checklist and retry.');
+        }
+      } catch {
+        if (cancelled) return;
+        setAgyAckBypassEnabled(false);
+        setLocalError('Power user mode is off. Complete the AGY checklist and retry.');
+      } finally {
+        if (!cancelled) {
+          setAgyAckBypassLoading(false);
+        }
+      }
+    };
+
+    void syncBypassState();
+
+    return () => {
+      cancelled = true;
+    };
+  }, [agyAckBypassEnabled, authFlow.error, fetchAgyBypassState, open, provider]);
 
   // When authFlow completes successfully (polling detected success), apply preset and close
   useEffect(() => {
@@ -226,7 +272,7 @@ export function AddAccountDialog({
       riskAcknowledgement: requiresAgyResponsibilityFlow
         ? {
             version: ANTIGRAVITY_ACK_VERSION,
-            reviewedIssue622: agyRiskChecklist.reviewedIssue622,
+            reviewedIssue509: agyRiskChecklist.reviewedIssue509,
             understandsBanRisk: agyRiskChecklist.understandsBanRisk,
             acceptsFullResponsibility: agyRiskChecklist.acceptsFullResponsibility,
             typedPhrase: agyRiskChecklist.typedPhrase,
diff --git a/ui/src/hooks/use-cliproxy-auth-flow.ts b/ui/src/hooks/use-cliproxy-auth-flow.ts
index 4f8bb8f9..c31c42e8 100644
--- a/ui/src/hooks/use-cliproxy-auth-flow.ts
+++ b/ui/src/hooks/use-cliproxy-auth-flow.ts
@@ -30,7 +30,7 @@ interface StartAuthOptions {
   startEndpoint?: 'start' | 'start-url';
   riskAcknowledgement?: {
     version: string;
-    reviewedIssue622: boolean;
+    reviewedIssue509: boolean;
     understandsBanRisk: boolean;
     acceptsFullResponsibility: boolean;
     typedPhrase: string;
@@ -42,6 +42,19 @@ const POLL_INTERVAL = 3000;
 /** Maximum polling duration (5 minutes) */
 const MAX_POLL_DURATION = 5 * 60 * 1000;
 
+async function parseResponseBody(response: Response): Promise<Record<string, unknown>> {
+  const text = await response.text();
+  if (!text) return {};
+
+  try {
+    return JSON.parse(text) as Record<string, unknown>;
+  } catch {
+    const fallbackError =
+      response.status >= 400 ? `Request failed with status ${response.status}` : undefined;
+    return fallbackError ? { error: fallbackError } : {};
+  }
+}
+
 /** Initial state for auth flow - extracted for DRY */
 const INITIAL_STATE: AuthFlowState = {
   provider: null,
@@ -206,8 +219,9 @@ export function useCliproxyAuthFlow() {
             signal: controller.signal,
           })
             .then(async (response) => {
-              const data = await response.json();
-              if (response.ok && data.success) {
+              const data = await parseResponseBody(response);
+              const success = data.success === true;
+              if (response.ok && success) {
                 queryClient.invalidateQueries({ queryKey: ['cliproxy-auth'] });
                 queryClient.invalidateQueries({ queryKey: ['account-quota'] });
                 // Note: No toast here - DeviceCodeDialog's useDeviceCode hook handles success toast
@@ -215,7 +229,8 @@ export function useCliproxyAuthFlow() {
                 openedAuthUrlRef.current = false;
                 setState(INITIAL_STATE);
               } else {
-                const errorMsg = data.error || 'Authentication failed';
+                const errorMsg =
+                  typeof data.error === 'string' ? data.error : 'Authentication failed';
                 toast.error(errorMsg);
                 setState((prev) => ({
                   ...prev,
@@ -247,30 +262,35 @@ export function useCliproxyAuthFlow() {
             signal: controller.signal,
           });
 
-          const data = await response.json();
+          const data = await parseResponseBody(response);
+          const success = data.success === true;
 
-          if (!response.ok || !data.success) {
-            throw new Error(data.error || 'Failed to start OAuth');
+          if (!response.ok || !success) {
+            const errorMsg = typeof data.error === 'string' ? data.error : 'Failed to start OAuth';
+            throw new Error(errorMsg);
           }
 
+          const authUrl = typeof data.authUrl === 'string' ? data.authUrl : null;
+          const oauthState = typeof data.state === 'string' ? data.state : null;
+
           // Update state with auth URL
           setState((prev) => ({
             ...prev,
-            authUrl: data.authUrl || null,
-            oauthState: data.state,
+            authUrl,
+            oauthState,
           }));
 
           // Auto-open auth URL in new browser tab (fallback URL still shown in dialog)
-          if (data.authUrl) {
+          if (authUrl) {
             openedAuthUrlRef.current = true;
-            window.open(data.authUrl, '_blank');
+            window.open(authUrl, '_blank');
           }
 
           // Start polling for completion
-          if (data.state) {
+          if (oauthState) {
             pollStartRef.current = Date.now();
             pollIntervalRef.current = setInterval(() => {
-              pollStatus(provider, data.state);
+              pollStatus(provider, oauthState);
             }, POLL_INTERVAL);
           }
         }
@@ -319,16 +339,19 @@ export function useCliproxyAuthFlow() {
           body: JSON.stringify({ redirectUrl }),
         });
 
-        const data = await response.json();
+        const data = await parseResponseBody(response);
+        const success = data.success === true;
 
-        if (response.ok && data.success) {
+        if (response.ok && success) {
           stopPolling();
           queryClient.invalidateQueries({ queryKey: ['cliproxy-auth'] });
           queryClient.invalidateQueries({ queryKey: ['account-quota'] });
           toast.success(`${state.provider} authentication successful`);
           setState(INITIAL_STATE);
         } else {
-          throw new Error(data.error || 'Callback submission failed');
+          const errorMsg =
+            typeof data.error === 'string' ? data.error : 'Callback submission failed';
+          throw new Error(errorMsg);
         }
       } catch (error) {
         const message = error instanceof Error ? error.message : 'Failed to submit callback';
diff --git a/ui/src/pages/settings/sections/auth-section.tsx b/ui/src/pages/settings/sections/auth-section.tsx
index 6061629d..fec3c31b 100644
--- a/ui/src/pages/settings/sections/auth-section.tsx
+++ b/ui/src/pages/settings/sections/auth-section.tsx
@@ -3,7 +3,7 @@
  * Settings section for CLIProxy auth tokens (API key and management secret)
  */
 
-import { useEffect, useState, useCallback } from 'react';
+import { useEffect, useState, useCallback, useRef } from 'react';
 import { Button } from '@/components/ui/button';
 import { Input } from '@/components/ui/input';
 import { Alert, AlertDescription } from '@/components/ui/alert';
@@ -56,6 +56,7 @@ export default function AuthSection() {
   const [agyAckBypass, setAgyAckBypass] = useState(false);
   const [agyAckBypassLoading, setAgyAckBypassLoading] = useState(true);
   const [agyAckBypassSaving, setAgyAckBypassSaving] = useState(false);
+  const agyAckBypassSavingRef = useRef(false);
 
   // Fetch tokens
   const fetchTokens = useCallback(async () => {
@@ -117,6 +118,8 @@ export default function AuthSection() {
 
   // Save all changes
   const saveChanges = async () => {
+    if (agyAckBypassSaving) return;
+
     const hasApiKeyChange = editedApiKey !== null && editedApiKey !== tokens?.apiKey.value;
     const hasSecretChange =
       editedSecret !== null && editedSecret !== tokens?.managementSecret.value;
@@ -156,6 +159,8 @@ export default function AuthSection() {
 
   // Regenerate management secret
   const regenerateSecret = async () => {
+    if (agyAckBypassSaving) return;
+
     try {
       setSaving(true);
       setError(null);
@@ -180,6 +185,8 @@ export default function AuthSection() {
 
   // Reset to defaults
   const resetToDefaults = async () => {
+    if (agyAckBypassSaving) return;
+
     try {
       setSaving(true);
       setError(null);
@@ -220,14 +227,17 @@ export default function AuthSection() {
   };
 
   const saveAgyAckBypass = async (nextValue: boolean) => {
+    if (agyAckBypassSavingRef.current || agyAckBypassSaving || saving) return;
+
     if (nextValue) {
       const confirmed = window.confirm(
-        'Enable Antigravity power user mode?\n\nThis disables AGY responsibility checklist prompts in CLI and dashboard. You accept full responsibility for OAuth/account risk.'
+        'Enable AGY power user mode?\n\nThis skips AGY safety prompts. You accept the OAuth risk.'
       );
       if (!confirmed) return;
     }
 
     try {
+      agyAckBypassSavingRef.current = true;
       setAgyAckBypassSaving(true);
       setError(null);
 
@@ -250,10 +260,18 @@ export default function AuthSection() {
     } catch (err) {
       setError(err instanceof Error ? err.message : 'Unknown error');
     } finally {
+      agyAckBypassSavingRef.current = false;
       setAgyAckBypassSaving(false);
     }
   };
 
+  const refreshAll = async () => {
+    if (loading || saving || agyAckBypassSaving) return;
+    setError(null);
+    setSuccess(null);
+    await Promise.all([fetchTokens(), fetchAgyAckBypass(), fetchRawConfig()]);
+  };
+
   if (loading || !tokens) {
     return (
       <div className="flex-1 flex items-center justify-center">
@@ -326,7 +344,7 @@ export default function AuthSection() {
                   value={displayApiKey}
                   onChange={(e) => setEditedApiKey(e.target.value)}
                   placeholder="API key"
-                  disabled={saving}
+                  disabled={saving || agyAckBypassSaving}
                   className="pr-20 font-mono text-sm"
                 />
                 <div className="absolute right-2 top-1/2 -translate-y-1/2 flex gap-1">
@@ -377,7 +395,7 @@ export default function AuthSection() {
                   value={displaySecret}
                   onChange={(e) => setEditedSecret(e.target.value)}
                   placeholder="Management secret"
-                  disabled={saving}
+                  disabled={saving || agyAckBypassSaving}
                   className="pr-20 font-mono text-sm"
                 />
                 <div className="absolute right-2 top-1/2 -translate-y-1/2 flex gap-1">
@@ -408,7 +426,7 @@ export default function AuthSection() {
                 variant="outline"
                 size="sm"
                 onClick={regenerateSecret}
-                disabled={saving}
+                disabled={saving || agyAckBypassSaving}
                 title="Generate new secure secret"
               >
                 <Sparkles className="w-4 h-4" />
@@ -429,15 +447,23 @@ export default function AuthSection() {
                 </p>
               </div>
               <Switch
+                aria-labelledby="agy-power-user-mode-label"
+                aria-describedby="agy-power-user-mode-description"
                 checked={agyAckBypass}
                 disabled={agyAckBypassLoading || agyAckBypassSaving || saving}
                 onCheckedChange={saveAgyAckBypass}
               />
             </div>
-            <p className="text-xs text-amber-800/90 dark:text-amber-200/90">
-              Use only if you fully understand the OAuth suspension/ban risk pattern (#622). CCS
+            <p
+              id="agy-power-user-mode-description"
+              className="text-xs text-amber-800/90 dark:text-amber-200/90"
+            >
+              Use only if you fully understand the OAuth suspension/ban risk pattern (#509). CCS
               cannot assume responsibility for account loss.
             </p>
+            <span id="agy-power-user-mode-label" className="sr-only">
+              Toggle AGY power user mode
+            </span>
           </div>
 
           <div className="pt-4 border-t">
@@ -445,7 +471,11 @@ export default function AuthSection() {
               variant="outline"
               size="sm"
               onClick={resetToDefaults}
-              disabled={saving || (!tokens.apiKey.isCustom && !tokens.managementSecret.isCustom)}
+              disabled={
+                saving ||
+                agyAckBypassSaving ||
+                (!tokens.apiKey.isCustom && !tokens.managementSecret.isCustom)
+              }
               className="gap-2"
             >
               <RotateCcw className="w-4 h-4" />
@@ -463,12 +493,8 @@ export default function AuthSection() {
         <Button
           variant="outline"
           size="sm"
-          onClick={() => {
-            fetchTokens();
-            fetchAgyAckBypass();
-            fetchRawConfig();
-          }}
-          disabled={loading || saving}
+          onClick={refreshAll}
+          disabled={loading || saving || agyAckBypassSaving}
           className="flex-1"
         >
           <RefreshCw className={`w-4 h-4 mr-2 ${loading ? 'animate-spin' : ''}`} />
@@ -478,7 +504,7 @@ export default function AuthSection() {
           variant="default"
           size="sm"
           onClick={saveChanges}
-          disabled={!hasChanges || saving}
+          disabled={!hasChanges || saving || agyAckBypassSaving}
           className="flex-1"
         >
           <Save className={`w-4 h-4 mr-2 ${saving ? 'animate-pulse' : ''}`} />