Fix school browser initialization and redirect detection; improve diagnostics

mobile/test/school/undergraduate_session_test.dart

@@ -31,6 +31,48 @@ void main() {
     session = UndergraduateSession();
   });
   tearDown(() => session.dispose());
+  test(
+    'page-finished during an old probe is retried on the redirected portal',
+    () async {
+      await session.openTimetable();
+      var first = true;
+      platform.web.javascript = (_) async {
+        if (first) {
+          first = false;
+          platform.web.url = 'https://eams.uestc.edu.cn/eams/home.action';
+          platform.delegate.finished(platform.web.url!);
+        }
+        return underEvidence(platform.web.url!);
+      };
+      platform.delegate.finished(platform.web.url!);
+      await flushSchoolEvents();
+      await Future<void>.delayed(const Duration(milliseconds: 600));
+      await flushSchoolEvents();
+      expect(session.statusLabel, '已连接');
+      expect(session.busy, isFalse);
+    },
+  );
+  test('a redirect between page callback and probe does not permanently stop login detection', () async {
+    await session.openTimetable();
+    var redirect = true;
+    platform.web.javascript = (_) async {
+      if (redirect) {
+        redirect = false;
+        platform.web.url = 'https://idas.uestc.edu.cn/authserver/login';
+        return underEvidence(platform.web.url!, authenticated: false);
+      }
+      return underEvidence(platform.web.url!);
+    };
+    platform.delegate.finished(platform.web.url!);
+    await flushSchoolEvents();
+    expect(session.message, isNot(contains('未完成')));
+    platform.delegate.finished(platform.web.url!);
+    await flushSchoolEvents();
+    platform.web.url = 'https://eams.uestc.edu.cn/eams/';
+    platform.delegate.finished(platform.web.url!);
+    await flushSchoolEvents();
+    expect(session.statusLabel, '已连接');
+  });
   test(
     'activating a loading browser never probes the previous blank document',
     () async {