OIDC로 빠지는 분기 점검 login_challenge 복구 fallback 추가

userfront/test/login_challenge_resolver_test.dart

@@ -0,0 +1,69 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:userfront/features/auth/domain/login_challenge_resolver.dart';
+
+void main() {
+  group('login_challenge_resolver', () {
+    test('widget 값이 있으면 최우선으로 사용', () {
+      final resolved = resolveLoginChallenge(
+        widgetLoginChallenge: 'widget-challenge',
+        uri: Uri.parse('/ko/login'),
+        rawSearch: '?login_challenge=raw-search',
+        rawHref: 'https://sso-test.hmac.kr/ko/login?login_challenge=raw-href',
+      );
+
+      expect(resolved.value, 'widget-challenge');
+      expect(resolved.source, LoginChallengeSource.widget);
+    });
+
+    test('widget 값이 없으면 URI query에서 복구', () {
+      final resolved = resolveLoginChallenge(
+        widgetLoginChallenge: null,
+        uri: Uri.parse('/ko/login?login_challenge=uri-query'),
+        rawSearch: '',
+        rawHref: '',
+      );
+
+      expect(resolved.value, 'uri-query');
+      expect(resolved.source, LoginChallengeSource.uriQuery);
+    });
+
+    test('URI query가 비어 있으면 raw search에서 복구', () {
+      final resolved = resolveLoginChallenge(
+        widgetLoginChallenge: null,
+        uri: Uri.parse('/ko/login'),
+        rawSearch: '?login_challenge=raw-search-value&x=1',
+        rawHref: '',
+      );
+
+      expect(resolved.value, 'raw-search-value');
+      expect(resolved.source, LoginChallengeSource.rawSearch);
+      expect(resolved.rawSearchHasLoginChallenge, isTrue);
+    });
+
+    test('raw search도 비어 있으면 raw href에서 복구', () {
+      final resolved = resolveLoginChallenge(
+        widgetLoginChallenge: null,
+        uri: Uri.parse('/ko/login'),
+        rawSearch: '',
+        rawHref:
+            'https://sso-test.hmac.kr/ko/login?a=1&login_challenge=raw-href-value#fragment',
+      );
+
+      expect(resolved.value, 'raw-href-value');
+      expect(resolved.source, LoginChallengeSource.rawHref);
+      expect(resolved.rawHrefHasLoginChallenge, isTrue);
+    });
+
+    test('값이 전부 없으면 missing', () {
+      final resolved = resolveLoginChallenge(
+        widgetLoginChallenge: null,
+        uri: Uri.parse('/ko/login'),
+        rawSearch: '',
+        rawHref: 'https://sso-test.hmac.kr/ko/login?x=1',
+      );
+
+      expect(resolved.value, isNull);
+      expect(resolved.source, LoginChallengeSource.missing);
+    });
+  });
+}