diff --git a/src/components/features/export/GoogleDriveAuthModal.tsx b/src/components/features/export/GoogleDriveAuthModal.tsx
index acf122247..5bfe3c09d 100644
--- a/src/components/features/export/GoogleDriveAuthModal.tsx
+++ b/src/components/features/export/GoogleDriveAuthModal.tsx
@@ -1,4 +1,4 @@
-import { useState } from 'react';
+import { useEffect } from 'react';
 import { useTranslation } from 'react-i18next';
 import { Dialog, DialogContent, DialogDescription, DialogHeader, DialogTitle } from '@/components/ui/dialog';
 import { Button } from '@/components/ui/button';
@@ -6,6 +6,7 @@ import { useAuth } from '@/lib/supabase/AuthProvider';
 import GoogleDocsIcon from '@/components/icons/GoogleDocsIcon';
 import { ExternalLink, Loader2 } from 'lucide-react';
 import { useToast } from '@/hooks/use-toast';
+import { useExternalRedirectPending } from '@/hooks/use-external-redirect-pending';
 
 interface GoogleDriveAuthModalProps {
   open: boolean;
@@ -16,14 +17,17 @@ export function GoogleDriveAuthModal({ open, onOpenChange }: GoogleDriveAuthModa
   const { t } = useTranslation();
   const { signInWithGoogle } = useAuth();
   const { toast } = useToast();
-  const [isConnecting, setIsConnecting] = useState(false);
+  const { pending: isConnecting, run: runRedirect, reset: resetRedirect } = useExternalRedirectPending();
+
+  // Callers keep this dialog mounted while closed; reopening starts fresh.
+  useEffect(() => {
+    if (!open) resetRedirect();
+  }, [open, resetRedirect]);
 
   const handleConnect = async () => {
-    setIsConnecting(true);
     try {
-      await signInWithGoogle({ driveAccess: true });
+      await runRedirect(() => signInWithGoogle({ driveAccess: true }));
     } catch (error) {
-      setIsConnecting(false);
       toast({
         title: t('googleDriveAuth.failedTitle', 'Could not open Google'),
         description: error instanceof Error ? error.message : t('googleDriveAuth.failedDesc', 'Please try again.'),
diff --git a/src/components/features/subscription/PricingModal.tsx b/src/components/features/subscription/PricingModal.tsx
index a427c98f8..c732dd18f 100644
--- a/src/components/features/subscription/PricingModal.tsx
+++ b/src/components/features/subscription/PricingModal.tsx
@@ -1,4 +1,4 @@
-import { useState } from 'react';
+import { useEffect, useState } from 'react';
 import { useTranslation } from 'react-i18next';
 import { Dialog, DialogContent, DialogHeader, DialogTitle, DialogDescription } from '@/components/ui/dialog';
 import { Button } from '@/components/ui/button';
@@ -8,6 +8,7 @@ import { Check, Sparkles, Zap, Crown } from 'lucide-react';
 import { redirectToCheckout, redeemPromoCode } from '@/lib/stripe';
 import { useToast } from '@/hooks/use-toast';
 import { useSubscription } from '@/hooks/use-subscription';
+import { useExternalRedirectPending } from '@/hooks/use-external-redirect-pending';
 
 interface PricingModalProps {
   open: boolean;
@@ -19,10 +20,16 @@ export function PricingModal({ open, onOpenChange, onPromoRedeemed }: PricingMod
   const { t } = useTranslation();
   const [promoCode, setPromoCode] = useState('');
   const [promoLoading, setPromoLoading] = useState(false);
-  const [checkoutLoading, setCheckoutLoading] = useState(false);
+  const { pending: checkoutLoading, run: runCheckout, reset: resetCheckout } = useExternalRedirectPending();
   const [showPromo, setShowPromo] = useState(false);
   const { toast } = useToast();
 
+  // The modal stays mounted while closed, so reopening it must not show a
+  // button still waiting on a checkout the user already left.
+  useEffect(() => {
+    if (!open) resetCheckout();
+  }, [open, resetCheckout]);
+
   const FREE_FEATURES = [
     t('pricingModal.freeFeature1'),
     t('pricingModal.freeFeature2'),
@@ -39,16 +46,14 @@ export function PricingModal({ open, onOpenChange, onPromoRedeemed }: PricingMod
   ];
 
   const handleUpgrade = async () => {
-    setCheckoutLoading(true);
     try {
-      await redirectToCheckout(promoCode || undefined);
+      await runCheckout(() => redirectToCheckout(promoCode || undefined));
     } catch (err) {
       toast({
         title: t('pricingModal.checkoutError'),
         description: err instanceof Error ? err.message : t('pricingModal.checkoutErrorDesc'),
         variant: 'destructive',
       });
-      setCheckoutLoading(false);
     }
   };
 
diff --git a/src/hooks/use-external-redirect-pending.test.tsx b/src/hooks/use-external-redirect-pending.test.tsx
new file mode 100644
index 000000000..6d323397f
--- /dev/null
+++ b/src/hooks/use-external-redirect-pending.test.tsx
@@ -0,0 +1,94 @@
+import { act, renderHook } from '@testing-library/react';
+import { afterEach, describe, expect, it, vi } from 'vitest';
+import { useExternalRedirectPending } from './use-external-redirect-pending';
+import { restoreFromBackForwardCache, restoreVisibility, setVisibility } from '@/test/helpers/page-lifecycle';
+
+function deferred() {
+  let resolve!: () => void;
+  const promise = new Promise<void>((r) => { resolve = r; });
+  return { promise, resolve };
+}
+
+afterEach(() => {
+  restoreVisibility();
+  vi.useRealTimers();
+});
+
+describe('useExternalRedirectPending', () => {
+  it('clears pending when the page comes back from the back/forward cache', async () => {
+    const { result } = renderHook(() => useExternalRedirectPending());
+    await act(() => result.current.run(async () => undefined));
+    expect(result.current.pending).toBe(true);
+
+    restoreFromBackForwardCache();
+    expect(result.current.pending).toBe(false);
+  });
+
+  it('starts one navigation per click while pending', async () => {
+    const navigate = vi.fn(async () => undefined);
+    const { result } = renderHook(() => useExternalRedirectPending());
+    await act(async () => {
+      await Promise.all([result.current.run(navigate), result.current.run(navigate)]);
+    });
+    expect(navigate).toHaveBeenCalledTimes(1);
+  });
+
+  it('keeps pending through tab switches and the timeout until the request resolves', async () => {
+    vi.useFakeTimers();
+    const request = deferred();
+    const { result } = renderHook(() => useExternalRedirectPending(1000));
+    let running!: Promise<void>;
+    act(() => { running = result.current.run(() => request.promise); });
+
+    setVisibility('hidden');
+    setVisibility('visible');
+    act(() => { vi.advanceTimersByTime(5000); });
+    expect(result.current.pending).toBe(true);
+
+    await act(async () => {
+      request.resolve();
+      await running;
+    });
+    setVisibility('hidden');
+    setVisibility('visible');
+    expect(result.current.pending).toBe(false);
+  });
+
+  it('gives up waiting after the safety timeout', async () => {
+    vi.useFakeTimers();
+    const { result } = renderHook(() => useExternalRedirectPending(1000));
+    await act(() => result.current.run(async () => undefined));
+    act(() => { vi.advanceTimersByTime(999); });
+    expect(result.current.pending).toBe(true);
+    act(() => { vi.advanceTimersByTime(1); });
+    expect(result.current.pending).toBe(false);
+  });
+
+  it('clears pending and rethrows when the navigation fails', async () => {
+    const { result } = renderHook(() => useExternalRedirectPending());
+    await act(async () => {
+      await expect(result.current.run(async () => { throw new Error('no url'); })).rejects.toThrow('no url');
+    });
+    expect(result.current.pending).toBe(false);
+  });
+
+  it('keeps blocking a second request when reset while the first is still running', async () => {
+    const request = deferred();
+    const navigate = vi.fn(() => request.promise);
+    const { result } = renderHook(() => useExternalRedirectPending());
+    let running!: Promise<void>;
+    act(() => { running = result.current.run(navigate); });
+
+    act(() => result.current.reset());
+    expect(result.current.pending).toBe(true);
+    await act(() => result.current.run(navigate));
+    expect(navigate).toHaveBeenCalledTimes(1);
+
+    await act(async () => {
+      request.resolve();
+      await running;
+    });
+    act(() => result.current.reset());
+    expect(result.current.pending).toBe(false);
+  });
+});
diff --git a/src/hooks/use-external-redirect-pending.ts b/src/hooks/use-external-redirect-pending.ts
new file mode 100644
index 000000000..e85fbc55b
--- /dev/null
+++ b/src/hooks/use-external-redirect-pending.ts
@@ -0,0 +1,70 @@
+import { useCallback, useEffect, useRef, useState } from 'react';
+
+const SAFETY_TIMEOUT_MS = 8000;
+
+/**
+ * Pending state for a button that leaves the site (Google sign-in, Stripe
+ * Checkout or portal). `run` sets pending, awaits the navigation helper, and
+ * clears pending if it throws. When the user comes back with Back, the browser
+ * may restore this page from the back/forward cache with React state frozen,
+ * so pending is also cleared on a persisted `pageshow`, when the page becomes
+ * visible again after it hid, and a few seconds after navigation started.
+ *
+ * Nothing clears pending while the helper is still running, `reset` included:
+ * the helper ends in a navigation that can't be cancelled, so releasing the
+ * button early would let a second click start a second request.
+ */
+export function useExternalRedirectPending(timeoutMs = SAFETY_TIMEOUT_MS) {
+  const [pending, setPending] = useState(false);
+  const pendingRef = useRef(false);
+  const requestingRef = useRef(false);
+  const hiddenRef = useRef(false);
+  const timerRef = useRef<ReturnType<typeof setTimeout>>();
+
+  const clear = useCallback(() => {
+    clearTimeout(timerRef.current);
+    pendingRef.current = false;
+    hiddenRef.current = false;
+    setPending(false);
+  }, []);
+
+  const reset = useCallback(() => {
+    if (!requestingRef.current) clear();
+  }, [clear]);
+
+  const run = useCallback(async (navigate: () => Promise<void>) => {
+    if (pendingRef.current) return;
+    pendingRef.current = true;
+    requestingRef.current = true;
+    setPending(true);
+    try {
+      await navigate();
+    } catch (error) {
+      requestingRef.current = false;
+      clear();
+      throw error;
+    }
+    requestingRef.current = false;
+    timerRef.current = setTimeout(clear, timeoutMs);
+  }, [clear, timeoutMs]);
+
+  useEffect(() => {
+    const onPageShow = (event: PageTransitionEvent) => {
+      if (event.persisted && pendingRef.current) reset();
+    };
+    const onVisibilityChange = () => {
+      if (!pendingRef.current || requestingRef.current) return;
+      if (document.visibilityState === 'hidden') hiddenRef.current = true;
+      else if (hiddenRef.current) clear();
+    };
+    window.addEventListener('pageshow', onPageShow);
+    document.addEventListener('visibilitychange', onVisibilityChange);
+    return () => {
+      window.removeEventListener('pageshow', onPageShow);
+      document.removeEventListener('visibilitychange', onVisibilityChange);
+      clearTimeout(timerRef.current);
+    };
+  }, [clear, reset]);
+
+  return { pending, run, reset };
+}
diff --git a/src/pages/LoginPage.tsx b/src/pages/LoginPage.tsx
index f07fcf9f7..6d0aebd3c 100644
--- a/src/pages/LoginPage.tsx
+++ b/src/pages/LoginPage.tsx
@@ -9,6 +9,7 @@ import { Tabs, TabsContent, TabsList, TabsTrigger } from '@/components/ui/tabs';
 import { ArrowLeft } from 'lucide-react';
 import { useAuth } from '@/lib/supabase/AuthProvider';
 import { useToast } from '@/hooks/use-toast';
+import { useExternalRedirectPending } from '@/hooks/use-external-redirect-pending';
 import { consumeWorkspaceInvite } from '@/lib/workspace/invite-handoff';
 import { localizeAuthError } from '@/lib/auth-errors';
 import { clearSessionExpiredNotice, sessionExpiredNotice } from '@/lib/supabase/session-expiry';
@@ -31,7 +32,7 @@ function isAuthMode(value: string): value is AuthMode {
 
 export default function LoginPage() {
   const { user, signInWithGoogle, signInWithEmailOtp, verifyEmailOtp, signInWithDemoCode } = useAuth();
-  const [isRedirecting, setIsRedirecting] = useState(false);
+  const { pending: isRedirecting, run: runRedirect } = useExternalRedirectPending();
   const [authMode, setAuthMode] = useState<AuthMode>('email');
   const [authStatus, setAuthStatus] = useState<AuthStatus>('idle');
   const [email, setEmail] = useState('');
@@ -70,11 +71,9 @@ export default function LoginPage() {
   }, [authStatus, authMode, emailSent]);
 
   const handleGoogleSignIn = async () => {
-    setIsRedirecting(true);
     try {
-      await signInWithGoogle();
+      await runRedirect(() => signInWithGoogle());
     } catch (error) {
-      setIsRedirecting(false);
       toast({
         title: t('login.failed', 'Could not start sign in'),
         description: localizeAuthError(error, t, 'login.tryAgain', 'Please try again.'),
diff --git a/src/pages/SettingsPage.tsx b/src/pages/SettingsPage.tsx
index 5ddf2a2df..4f6042d66 100644
--- a/src/pages/SettingsPage.tsx
+++ b/src/pages/SettingsPage.tsx
@@ -25,6 +25,7 @@ import { supabase } from '@/lib/supabase/client';
 import { getActiveEnv } from '@/lib/supabase/env';
 import { useToast } from '@/hooks/use-toast';
 import { useSubscription } from '@/hooks/use-subscription';
+import { useExternalRedirectPending } from '@/hooks/use-external-redirect-pending';
 import { redirectToPortal } from '@/lib/stripe';
 import { deleteAccount, downloadAccountData } from '@/lib/account';
 import { PricingModal } from '@/components/features/subscription/PricingModal';
@@ -80,7 +81,7 @@ export default function SettingsPage() {
   const signInMethod = signInMethodKey(user);
   const subscription = useSubscription();
   const [pricingOpen, setPricingOpen] = useState(false);
-  const [portalLoading, setPortalLoading] = useState(false);
+  const { pending: portalLoading, run: runPortalRedirect } = useExternalRedirectPending();
   const [deleteDialogOpen, setDeleteDialogOpen] = useState(false);
   const [deleteEmail, setDeleteEmail] = useState('');
   const [exporting, setExporting] = useState(false);
@@ -226,9 +227,8 @@ export default function SettingsPage() {
   };
 
   const handleManageSubscription = async () => {
-    setPortalLoading(true);
     try {
-      await redirectToPortal();
+      await runPortalRedirect(redirectToPortal);
     } catch (err) {
       const message = err instanceof Error ? err.message : 'Failed to open billing portal';
       if (message.toLowerCase().includes('no active subscription')) {
@@ -244,7 +244,6 @@ export default function SettingsPage() {
           variant: 'destructive',
         });
       }
-      setPortalLoading(false);
     }
   };
 
diff --git a/src/test/auth/login-google-redirect.test.tsx b/src/test/auth/login-google-redirect.test.tsx
new file mode 100644
index 000000000..49a1e3f86
--- /dev/null
+++ b/src/test/auth/login-google-redirect.test.tsx
@@ -0,0 +1,41 @@
+import { describe, expect, it, vi } from 'vitest';
+import { fireEvent, render, screen, waitFor } from '@testing-library/react';
+import { MemoryRouter } from 'react-router-dom';
+import LoginPage from '@/pages/LoginPage';
+import { restoreFromBackForwardCache } from '@/test/helpers/page-lifecycle';
+
+const auth = vi.hoisted(() => ({
+  // Resolves once location.assign has been called, like the real one.
+  signInWithGoogle: vi.fn(async () => undefined),
+}));
+
+vi.mock('@/lib/supabase/AuthProvider', () => ({
+  useAuth: () => ({
+    user: null as null,
+    signInWithGoogle: auth.signInWithGoogle,
+    signInWithEmailOtp: vi.fn(),
+    verifyEmailOtp: vi.fn(),
+    signInWithDemoCode: vi.fn(),
+  }),
+}));
+
+// AUTH-15: Back from Google's account chooser restored /login from the
+// back/forward cache with the button stuck on "Redirecting...".
+describe('Continue with Google', () => {
+  it('works again after Back from Google restores the page', async () => {
+    render(<MemoryRouter><LoginPage /></MemoryRouter>);
+
+    fireEvent.click(screen.getByRole('button', { name: 'Continue with Google' }));
+    const redirecting = await screen.findByRole('button', { name: 'Redirecting...' });
+    expect(redirecting).toBeDisabled();
+    fireEvent.click(redirecting);
+    expect(auth.signInWithGoogle).toHaveBeenCalledTimes(1);
+
+    restoreFromBackForwardCache();
+    const button = screen.getByRole('button', { name: 'Continue with Google' });
+    expect(button).toBeEnabled();
+
+    fireEvent.click(button);
+    await waitFor(() => expect(auth.signInWithGoogle).toHaveBeenCalledTimes(2));
+  });
+});
diff --git a/src/test/billing/pricing-modal-redirect.test.tsx b/src/test/billing/pricing-modal-redirect.test.tsx
new file mode 100644
index 000000000..6e03f1eec
--- /dev/null
+++ b/src/test/billing/pricing-modal-redirect.test.tsx
@@ -0,0 +1,64 @@
+import { beforeEach, describe, expect, it, vi } from 'vitest';
+import { fireEvent, render, screen, waitFor } from '@testing-library/react';
+import { PricingModal } from '@/components/features/subscription/PricingModal';
+import { restoreFromBackForwardCache } from '@/test/helpers/page-lifecycle';
+
+const stripe = vi.hoisted(() => ({
+  redirectToCheckout: vi.fn(async (_promoCode?: string) => undefined),
+  redeemPromoCode: vi.fn(),
+}));
+
+vi.mock('@/lib/stripe', () => stripe);
+vi.mock('@/hooks/use-subscription', () => ({ useSubscription: () => ({ tier: 'trial' }) }));
+vi.mock('@/hooks/use-toast', () => ({ useToast: () => ({ toast: vi.fn() }) }));
+
+function renderModal(open = true) {
+  const props = { onOpenChange: vi.fn() };
+  const view = render(<PricingModal open={open} {...props} />);
+  return { ...view, reopen: (next: boolean) => view.rerender(<PricingModal open={next} {...props} />) };
+}
+
+async function startCheckout() {
+  fireEvent.click(screen.getByRole('button', { name: 'Upgrade Now' }));
+  const redirecting = await screen.findByRole('button', { name: 'Redirecting...' });
+  expect(redirecting).toBeDisabled();
+}
+
+// AUTH-16: Back from Stripe Checkout left Upgrade Now disabled, and closing
+// and reopening the dialog did not clear it.
+describe('PricingModal Upgrade Now', () => {
+  beforeEach(() => stripe.redirectToCheckout.mockClear());
+
+  it('works again after Back from Checkout restores the page', async () => {
+    renderModal();
+    await startCheckout();
+    fireEvent.click(screen.getByRole('button', { name: 'Redirecting...' }));
+    expect(stripe.redirectToCheckout).toHaveBeenCalledTimes(1);
+
+    restoreFromBackForwardCache();
+    fireEvent.click(screen.getByRole('button', { name: 'Upgrade Now' }));
+    await waitFor(() => expect(stripe.redirectToCheckout).toHaveBeenCalledTimes(2));
+  });
+
+  it('shows a fresh button after the dialog is closed and reopened', async () => {
+    const { reopen } = renderModal();
+    await startCheckout();
+
+    reopen(false);
+    reopen(true);
+    expect(await screen.findByRole('button', { name: 'Upgrade Now' })).toBeEnabled();
+  });
+
+  it('sends one checkout request when reopened while the first is still loading', async () => {
+    let finish!: () => void;
+    stripe.redirectToCheckout.mockImplementationOnce(() => new Promise<undefined>((resolve) => { finish = () => resolve(undefined); }));
+    const { reopen } = renderModal();
+    await startCheckout();
+
+    reopen(false);
+    reopen(true);
+    fireEvent.click(await screen.findByRole('button', { name: 'Redirecting...' }));
+    expect(stripe.redirectToCheckout).toHaveBeenCalledTimes(1);
+    finish();
+  });
+});
diff --git a/src/test/helpers/page-lifecycle.ts b/src/test/helpers/page-lifecycle.ts
new file mode 100644
index 000000000..4909c05a6
--- /dev/null
+++ b/src/test/helpers/page-lifecycle.ts
@@ -0,0 +1,22 @@
+import { act } from '@testing-library/react';
+
+/** What a browser fires when it restores a page from the back/forward cache. */
+export function restoreFromBackForwardCache() {
+  const event = new Event('pageshow');
+  Object.defineProperty(event, 'persisted', { value: true });
+  act(() => {
+    window.dispatchEvent(event);
+  });
+}
+
+export function setVisibility(state: DocumentVisibilityState) {
+  Object.defineProperty(document, 'visibilityState', { configurable: true, get: () => state });
+  act(() => {
+    document.dispatchEvent(new Event('visibilitychange'));
+  });
+}
+
+/** Drops the override from setVisibility so jsdom's own getter applies again. */
+export function restoreVisibility() {
+  delete (document as { visibilityState?: unknown }).visibilityState;
+}