diff --git a/userfront-e2e/tests/oidc-login-challenge.spec.ts b/userfront-e2e/tests/oidc-login-challenge.spec.ts
new file mode 100644
index 00000000..920a69b4
--- /dev/null
+++ b/userfront-e2e/tests/oidc-login-challenge.spec.ts
@@ -0,0 +1,81 @@
+import { expect, test, type Page, type Route } from '@playwright/test';
+
+async function mockUserfrontApisForRepro(
+  page: Page,
+  options: { sessionStatus: number } = { sessionStatus: 401 },
+): Promise<void> {
+  await page.route('**/api/v1/**', async (route: Route) => {
+    const requestUrl = new URL(route.request().url());
+    const path = requestUrl.pathname;
+
+    if (path.endsWith('/api/v1/user/me')) {
+      await route.fulfill({
+        status: options.sessionStatus,
+        contentType: 'application/json',
+        body: JSON.stringify({ error: 'unauthorized' }),
+      });
+      return;
+    }
+
+    if (path.endsWith('/api/v1/client-log')) {
+      await route.fulfill({
+        status: 200,
+        contentType: 'application/json',
+        body: JSON.stringify({ ok: true }),
+      });
+      return;
+    }
+
+    // Default mock for other APIs
+    await route.fulfill({
+      status: 200,
+      contentType: 'application/json',
+      body: JSON.stringify({}),
+    });
+  });
+}
+
+test.describe('Issue #345 Reproduction (Log-based Validation)', () => {
+  test('비로그인 상태에서 login_challenge와 함께 signin 진입 시 루프 없이 로그가 정상 출력되어야 한다', async ({ page }) => {
+    const logs: string[] = [];
+    page.on('console', msg => {
+      const text = msg.text();
+      logs.push(text);
+      console.log(`[Browser] ${text}`);
+    });
+
+    const requests: string[] = [];
+    page.on('request', request => {
+      if (request.isNavigationRequest()) {
+        requests.push(request.url());
+      }
+    });
+
+    await mockUserfrontApisForRepro(page, { sessionStatus: 401 });
+
+    const targetUrl = '/ko/signin?login_challenge=repro_challenge_12345';
+    await page.goto(targetUrl);
+    
+    // WASM 앱 로딩 및 로직 실행 대기
+    await page.waitForTimeout(7000);
+
+    const currentUrl = page.url();
+    const signinNavigations = requests.filter(url => url.includes('/signin'));
+
+    // [검증 1] URL 유지 확인
+    expect(currentUrl).toContain('login_challenge=repro_challenge_12345');
+    
+    // [검증 2] 리다이렉트 루프 발생 여부 확인 (최초 진입 1회만 있어야 함)
+    expect(signinNavigations.length).toBeLessThanOrEqual(1);
+
+    // [검증 3] 핵심 로직 로그 확인 (성공의 결정적 증거)
+    // 이전에는 여기서 Exception이 발생했으나, 이제는 아래 로그가 찍혀야 함
+    const hasSuccessLog = logs.some(log => 
+      log.includes('[Auth] OIDC auto-accept: No active session (status: 401)')
+    );
+    
+    expect(hasSuccessLog).toBe(true);
+    
+    console.log('✅ 루프가 해결되었으며, 로그 검증을 통해 정상 동작을 확인했습니다.');
+  });
+});
diff --git a/userfront/lib/features/auth/presentation/login_screen.dart b/userfront/lib/features/auth/presentation/login_screen.dart
index 43f51370..5f23e16f 100644
--- a/userfront/lib/features/auth/presentation/login_screen.dart
+++ b/userfront/lib/features/auth/presentation/login_screen.dart
@@ -161,7 +161,12 @@ class _LoginScreenState extends ConsumerState<LoginScreen>
     final provider = pendingProvider ?? AuthTokenStore.getProvider() ?? 'ory';
 
     try {
-      await AuthProxyService.checkCookieSession();
+      final status = await AuthProxyService.getSessionStatus(useCookie: true);
+      if (status != 200) {
+        debugPrint("[Auth] Cookie session check: No active session (status: $status)");
+        return;
+      }
+
       if (!shouldPromoteCookieSession(
         currentToken: AuthTokenStore.getToken(),
         loginChallenge: loginChallenge,
@@ -242,11 +247,16 @@ class _LoginScreenState extends ConsumerState<LoginScreen>
     }
 
     try {
-      await AuthProxyService.checkCookieSession();
-      AuthTokenStore.setCookieMode(
-        provider: AuthTokenStore.getProvider() ?? 'ory',
-      );
-      await _acceptOidcLoginAndRedirect();
+      // 401 응답은 세션이 없는 정상적인 상태이므로 예외로 처리하지 않고 우아하게 중단합니다.
+      final status = await AuthProxyService.getSessionStatus(useCookie: true);
+      if (status == 200) {
+        AuthTokenStore.setCookieMode(
+          provider: AuthTokenStore.getProvider() ?? 'ory',
+        );
+        await _acceptOidcLoginAndRedirect();
+      } else {
+        debugPrint("[Auth] OIDC auto-accept: No active session (status: $status)");
+      }
     } catch (e) {
       debugPrint("[Auth] OIDC auto-accept cookie check failed: $e");
     }