fix(ui): prevent infinite spinner on factor-two without active 2FA session

Why:
Users navigating directly to /sign-in#/factor-two without an active
sign-in requiring 2FA would see an infinite loading spinner because
there was no status check to redirect them back to sign-in start.

What changed:
Added useEffect to SignInFactorTwo that redirects to sign-in start
when signIn.status is null, needs_identifier, or needs_first_factor.
Matches the existing pattern in SignInFactorOne.

Key detail: dependency array only includes __internal_setActiveInProgress
(not signIn.status) to avoid triggering redirect during valid sign-in
completion when status changes to null.

Author: nikosdouvlis

.changeset/fix-factor-two-infinite-spinner.md

@@ -0,0 +1,5 @@
+---
+'@clerk/ui': patch
+---
+
+Fix infinite loading spinner when navigating to factor-two sign-in route without an active 2FA session

packages/ui/src/components/SignIn/SignInFactorTwo.tsx

@@ -1,8 +1,12 @@
+import { useClerk } from '@clerk/shared/react';
+import React from 'react';
+
 import { withCardStateProvider } from '@/ui/elements/contexts';
 import { LoadingCard } from '@/ui/elements/LoadingCard';
 
 import { withRedirectToAfterSignIn, withRedirectToSignInTask } from '../../common';
 import { useCoreSignIn } from '../../contexts';
+import { useRouter } from '../../router';
 import { SignInFactorTwoAlternativeMethods } from './SignInFactorTwoAlternativeMethods';
 import { SignInFactorTwoBackupCodeCard } from './SignInFactorTwoBackupCodeCard';
 import { SignInFactorTwoEmailCodeCard } from './SignInFactorTwoEmailCodeCard';
@@ -12,7 +16,9 @@ import { SignInFactorTwoTOTPCard } from './SignInFactorTwoTOTPCard';
 import { useSecondFactorSelection } from './useSecondFactorSelection';
 
 function SignInFactorTwoInternal(): JSX.Element {
+  const { __internal_setActiveInProgress } = useClerk();
   const signIn = useCoreSignIn();
+  const router = useRouter();
   const {
     currentFactor,
     factorAlreadyPrepared,
@@ -22,6 +28,19 @@ function SignInFactorTwoInternal(): JSX.Element {
     toggleAllStrategies,
   } = useSecondFactorSelection(signIn.supportedSecondFactors);
 
+  React.useEffect(() => {
+    if (__internal_setActiveInProgress) {
+      return;
+    }
+
+    // If the sign-in was reset or doesn't exist, redirect back to the start.
+    // Don't redirect for 'complete' status - setActive will handle navigation.
+    if (signIn.status === null || signIn.status === 'needs_identifier' || signIn.status === 'needs_first_factor') {
+      void router.navigate('../');
+    }
+    // eslint-disable-next-line react-hooks/exhaustive-deps -- Match SignInFactorOne pattern: only run on mount and when setActiveInProgress changes
+  }, [__internal_setActiveInProgress]);
+
   if (!currentFactor) {
     return <LoadingCard />;
   }