userfront&backend test coverage 추가

userfront/test/login_challenge_resolver_test.dart

@@ -54,6 +54,37 @@ void main() {
       expect(resolved.rawHrefHasLoginChallenge, isTrue);
     });
 
+    test('raw query 파싱 실패 시 수동 파싱으로 복구하고 diagnostics를 남긴다', () {
+      final resolved = resolveLoginChallenge(
+        widgetLoginChallenge: '  ',
+        uri: Uri.parse('/ko/login'),
+        rawSearch: '?x=%E0%A4%A&login_challenge=manual%20value',
+        rawHref: '',
+      );
+
+      expect(resolved.value, 'manual value');
+      expect(resolved.source, LoginChallengeSource.rawSearch);
+      expect(resolved.toDiagnostics(), {
+        'resolved_value_len': 12,
+        'resolved_source': 'rawSearch',
+        'uri_has_login_challenge': false,
+        'raw_search_has_login_challenge': true,
+        'raw_href_has_login_challenge': false,
+      });
+    });
+
+    test('raw href가 일반 URI로 파싱되지 않아도 query 조각에서 복구한다', () {
+      final resolved = resolveLoginChallenge(
+        widgetLoginChallenge: null,
+        uri: Uri.parse('/ko/login'),
+        rawSearch: '?login_challenge',
+        rawHref: 'not a url ?login_challenge=href%20fallback#fragment',
+      );
+
+      expect(resolved.value, 'href fallback');
+      expect(resolved.source, LoginChallengeSource.rawHref);
+    });
+
     test('값이 전부 없으면 missing', () {
       final resolved = resolveLoginChallenge(
         widgetLoginChallenge: null,