fix: harden school imports and add optional feedback diagnostics

mobile/lib/features/school/school_session.dart

@@ -6,6 +6,7 @@ import 'package:webview_flutter/webview_flutter.dart';
 import '../../data/json_schedule_import.dart';
 import '../../domain/exam_schedule.dart';
 import '../../domain/school_term.dart';
+import '../../services/diagnostic_log.dart';
 import 'school_navigation_policy.dart';
 import 'school_page_adapter.dart';
 import 'school_exam_adapter.dart';
@@ -40,7 +41,10 @@ class SchoolSession extends ChangeNotifier {
               await web.loadRequest(upgrade);
             } catch (_) {
               if (generation == _pageGeneration) {
-                _failure('学校身份认证暂时无法打开，请重试。');
+                _failure(
+                  '学校身份认证暂时无法打开，请重试。',
+                  code: 'authentication_load_failed',
+                );
               }
             }
             return NavigationDecision.prevent;
@@ -55,12 +59,15 @@ class SchoolSession extends ChangeNotifier {
                 'Blocked school navigation origin: ${uri?.scheme}://${uri?.host}',
               );
             }
-            if (request.isMainFrame) _failure('学校跳转到了其他地址，请返回学校认证入口重试。');
+            if (request.isMainFrame) {
+              _failure('学校跳转到了其他地址，请返回学校认证入口重试。', code: 'blocked_navigation');
+            }
             return NavigationDecision.prevent;
           }
           return NavigationDecision.navigate;
         },
-        onPageStarted: (_) {
+        onPageStarted: (url) {
+          DiagnosticLog.instance.navigation('graduate', 'started', url);
           _poll?.cancel();
           _manualRead = false;
           _pageGeneration++;
@@ -79,7 +86,11 @@ class SchoolSession extends ChangeNotifier {
           if (hasOpened &&
               generation == _pageGeneration &&
               error.url == current) {
-            _failure('学校页面暂时未能加载，请检查网络后重试。');
+            _failure(
+              '学校页面暂时未能加载，请检查网络后重试。',
+              code: 'web_resource_error',
+              status: error.errorCode,
+            );
           }
         },
         onHttpError: (error) async {
@@ -89,7 +100,11 @@ class SchoolSession extends ChangeNotifier {
               generation == _pageGeneration &&
               error.request != null &&
               error.request!.uri == current) {
-            _failure('学校请求未完成，请稍后重试。');
+            _failure(
+              '学校请求未完成，请稍后重试。',
+              code: 'http_error',
+              status: error.response?.statusCode,
+            );
           }
         },
       ),
@@ -175,6 +190,14 @@ class SchoolSession extends ChangeNotifier {
     bool forceAuth = false,
   }) async {
     final serial = ++_openSerial;
+    DiagnosticLog.instance.add(
+      'login_opened',
+      fields: {
+        'school': 'graduate',
+        'phase': exams ? 'exams' : 'timetable',
+        'term': term?.id,
+      },
+    );
     final closing = _logoutFuture;
     if (closing != null) await closing;
     if (serial != _openSerial) return;
@@ -211,7 +234,7 @@ class SchoolSession extends ChangeNotifier {
       await web.loadRequest(connected ? _target : authUrl);
     } catch (_) {
       if (serial == _openSerial && generation == _pageGeneration) {
-        _failure('学校入口无法打开，请检查校园网络后重试。');
+        _failure('学校入口无法打开，请检查校园网络后重试。', code: 'entry_load_failed');
       }
     }
   }
@@ -244,7 +267,7 @@ class SchoolSession extends ChangeNotifier {
       await web.loadRequest(_target);
     } catch (_) {
       if (serial == _openSerial && generation == _pageGeneration) {
-        _failure('学校学期查询页面暂时无法打开，请重试。');
+        _failure('学校学期查询页面暂时无法打开，请重试。', code: 'query_load_failed');
       }
     }
   }
@@ -254,11 +277,20 @@ class SchoolSession extends ChangeNotifier {
     _timeout?.cancel();
     _timeout = Timer(
       const Duration(seconds: 45),
-      () => _failure('查找超时，请检查学校页面后重试。已有数据保持不变。'),
+      () => _failure('查找超时，请检查学校页面后重试。已有数据保持不变。', code: 'read_timeout'),
     );
   }
 
-  void _failure(String text) {
+  void _failure(String text, {String code = 'flow_failure', int? status}) {
+    DiagnosticLog.instance.add(
+      'school_read_failed',
+      fields: {
+        'school': 'graduate',
+        'code': code,
+        'status': status,
+        'term': selectedTerm?.id,
+      },
+    );
     if (!hasOpened || _routeClosed) return;
     _pageGeneration++;
     _reader.invalidate();
@@ -305,7 +337,7 @@ class SchoolSession extends ChangeNotifier {
     }
     _poll?.cancel();
     if (_pollsLeft-- <= 0) {
-      if (finding) _failure('查找超时，请检查学校页面后重试。已有数据保持不变。');
+      if (finding) _failure('查找超时，请检查学校页面后重试。已有数据保持不变。', code: 'read_timeout');
       return;
     }
     _poll = Timer(const Duration(milliseconds: 750), () {
@@ -320,6 +352,9 @@ class SchoolSession extends ChangeNotifier {
       );
 
   Future<void> _loaded(String url, {bool resetPolling = true}) async {
+    if (resetPolling) {
+      DiagnosticLog.instance.navigation('graduate', 'finished', url);
+    }
     if (!hasOpened || _routeClosed) return;
     final generation = _pageGeneration;
     final uri = Uri.tryParse(url);
@@ -360,6 +395,15 @@ class SchoolSession extends ChangeNotifier {
     }
     try {
       final evidence = await _evidence(uri);
+      DiagnosticLog.instance.add(
+        'school_evidence',
+        fields: {
+          'school': 'graduate',
+          'result': evidence.authenticated,
+          'count': evidence.pages.length,
+          'term': selectedTerm?.id,
+        },
+      );
       if (!hasOpened ||
           generation != _pageGeneration ||
           await web.currentUrl() != url) {
@@ -384,14 +428,26 @@ class SchoolSession extends ChangeNotifier {
           if (requestingExams) {
             final draft = SchoolExamAdapter.extract(page.html);
             if (generation != _pageGeneration) return;
-            if (draft.termId != selectedTerm?.id.toString()) continue;
+            if (draft.termId != selectedTerm?.id.toString()) {
+              DiagnosticLog.instance.add(
+                'term_mismatch',
+                fields: {'school': 'graduate'},
+              );
+              continue;
+            }
             pendingExams = draft;
           } else {
             // The probe validates the live document's origin. The strict parser
             // gets only its recognized fragment with the canonical table path.
             final draft = await _reader.read(_target, () async => page.html);
             if (!hasOpened || generation != _pageGeneration) return;
-            if (draft.schoolTerm != selectedTerm) continue;
+            if (draft.schoolTerm != selectedTerm) {
+              DiagnosticLog.instance.add(
+                'term_mismatch',
+                fields: {'school': 'graduate'},
+              );
+              continue;
+            }
             pendingDraft = draft;
           }
           _timeout?.cancel();
@@ -399,9 +455,27 @@ class SchoolSession extends ChangeNotifier {
           connectionState = SchoolConnectionState.connected;
           finding = true;
           message = '读取成功，正在保存…';
+          DiagnosticLog.instance.add(
+            'school_parsed',
+            fields: {
+              'school': 'graduate',
+              'phase': requestingExams ? 'exams' : 'timetable',
+              'count':
+                  pendingDraft?.courses.length ??
+                  pendingExams?.records.length ??
+                  0,
+            },
+          );
           notifyListeners();
           return;
-        } catch (_) {
+        } catch (error) {
+          DiagnosticLog.instance.add(
+            'school_parse_rejected',
+            fields: {
+              'school': 'graduate',
+              'code': error.runtimeType.toString(),
+            },
+          );
           if (generation != _pageGeneration) return;
           // A recognized table can still be incomplete during asynchronous load.
         }
@@ -411,6 +485,14 @@ class SchoolSession extends ChangeNotifier {
           ? null
           : _flow.onLoaded(uri, authenticated: evidence.authenticated);
       if (next != null) {
+        DiagnosticLog.instance.add(
+          'school_redirect_requested',
+          fields: {
+            'school': 'graduate',
+            'phase': requestingExams ? 'exams' : 'timetable',
+            'term': selectedTerm?.id,
+          },
+        );
         finding = true;
         _loading = true;
         message = _findingMessage;
@@ -420,14 +502,17 @@ class SchoolSession extends ChangeNotifier {
           await web.loadRequest(next);
         } catch (_) {
           if (generation == _pageGeneration) {
-            _failure('课表查询页面暂时无法打开，请重试。');
+            _failure('课表查询页面暂时无法打开，请重试。', code: 'query_load_failed');
           }
         }
         return;
       }
       if (!finding) message = '请在学校网页完成认证；进入研究生系统后会自动读取。';
-    } catch (_) {
-      // JavaScript and frame access can fail briefly while the page is changing.
+    } catch (error) {
+      DiagnosticLog.instance.add(
+        'school_probe_failed',
+        fields: {'school': 'graduate', 'code': error.runtimeType.toString()},
+      );
     } finally {
       if (_probeGeneration == generation) _probeGeneration = null;
       _scheduleProbe(url, generation);