fix: improve transfer recognition and local data safety

frontend/test/api_models_test.dart

@@ -1,12 +1,36 @@
 import 'dart:convert';
 
 import 'package:flutter_test/flutter_test.dart';
+import 'package:miaoji_zhang/shared/api/backend_identity.dart';
 import 'package:miaoji_zhang/shared/api/business_api.dart';
 import 'package:miaoji_zhang/shared/api/sse_frame_accumulator.dart';
 import 'package:miaoji_zhang/shared/services/current_ledger_store.dart';
 import 'package:miaoji_zhang/shared/widgets/app_icons.dart';
 
 void main() {
+  test('本地账号命名空间同时隔离后端和用户', () {
+    final first = BackendIdentity.accountNamespaceFor(
+      'https://api-a.example.com/',
+      1,
+    );
+    final normalized = BackendIdentity.accountNamespaceFor(
+      'https://API-A.example.com',
+      1,
+    );
+    final otherBackend = BackendIdentity.accountNamespaceFor(
+      'https://api-b.example.com',
+      1,
+    );
+    final otherUser = BackendIdentity.accountNamespaceFor(
+      'https://api-a.example.com',
+      2,
+    );
+
+    expect(first, normalized);
+    expect(first, isNot(otherBackend));
+    expect(first, isNot(otherUser));
+  });
+
   test(
     'SSE framing preserves split UTF-8 characters and trailing events',
     () async {

frontend/test/local_transfer_database_test.dart

@@ -82,4 +82,29 @@ void main() {
       throwsStateError,
     );
   });
+
+  test('云端回写失败时保留待同步的本地账单', () {
+    final database = LocalDatabase.inMemoryForTesting();
+    addTearDown(database.close);
+    final local = database.createTransaction({
+      'ledgerId': 1,
+      'categoryId': 1,
+      'type': 'expense',
+      'amount': 28,
+      'occurredAt': '2026-07-25T03:00:00.000Z',
+      'source': 'manual',
+    });
+    final localId = local['id'] as int;
+
+    expect(
+      () => database.replaceLocalTransaction(localId, {
+        ...local,
+        'id': 42,
+        'occurredAt': 'invalid-time',
+      }),
+      throwsFormatException,
+    );
+    expect(database.transaction(localId), isNotNull);
+    expect(database.transaction(42), isNull);
+  });
 }

frontend/test/visual_contract_test.dart

@@ -3,6 +3,21 @@ import 'dart:io';
 import 'package:flutter_test/flutter_test.dart';
 
 void main() {
+  test('登录强制刷新远端资料并按后端隔离本地账号数据', () {
+    final auth = File('lib/shared/api/auth_api.dart').readAsStringSync();
+    final session = File(
+      'lib/shared/services/session_store.dart',
+    ).readAsStringSync();
+
+    expect(auth, contains('me(forceRemote: true)'));
+    expect(auth, contains('if (!forceRemote &&'));
+    expect(session, contains('BackendIdentity.accountNamespace(userId)'));
+    expect(session, contains('pending_account_archive_namespace'));
+    expect(session, contains('last_account_namespace'));
+    final client = File('lib/shared/api/api_client.dart').readAsStringSync();
+    expect(client, contains("'auth_token_\${BackendIdentity.scope}'"));
+  });
+
   test('启动页只读取本地缓存，不等待远程接口', () {
     final source = File(
       'lib/features/auth/pages/splash_page.dart',