fix(app): picker dup gate — 2s server-check timeout, single snackbar, fileSize-throw allow

评审跟进三项（拦截面加固，判定口径不变）：

- 服务器半场时间帽：checkUploadDuplicates 竞速 serverCheckTimeout
  （构造参数，默认 2s）——弱网下点选不再静默挂到 dio 连接超时
  （10s）；超时=无命中，同各半场失败降级放行（底层请求不取消，
  dio 自身超时照常兜底）。测试 ⑥：永不回包适配器 + 注入 50ms 帽
  → 放行且请求确已发出；
- SnackBar 不堆积：呈现前 clearSnackBars——快速点多个重复资产
  只留当前一条（原会排队 N 条 4s 提示）。测试 ① 扩展：第二条
  隐藏后无排队等待的提示条；
- fileSize 失败路径钉住（测试 ⑦）：资产事实 fileSize 抛错 → 放行
  且两半场零查询。

Co-Authored-By: Claude Code <noreply@anthropic.com>

apps/mobile/test/features/uploads/enqueue_test.dart

@@ -12,6 +12,7 @@
 /// [PickerAssetFact] 记录绕开 AssetEntity.fileSize 的平台通道。
 library;
 
+import 'dart:async';
 import 'dart:io';
 
 import 'package:dio/dio.dart';
@@ -285,7 +286,34 @@ void main() {
         ),
         findsOneWidget,
       );
-      await drainBlockedSnackBar(tester, ctx);
+
+      // 不堆积：快速点另一个重复资产 → 旧条清除后只留一条（无 N×4s 队列）。
+      late bool otherBlocked;
+      await tester.runAsync(() async {
+        otherBlocked = await gate.decideFact(
+          ctx,
+          gateAsset(id: 'asset-2', bytes: kJpgBytes.length),
+          false,
+        );
+      });
+      expect(otherBlocked, isFalse, reason: '另一重复资产同样拦下');
+      await tester.pumpAndSettle();
+      expect(
+        find.text(
+          'Already uploaded to this album — tap again to select anyway',
+        ),
+        findsOneWidget,
+        reason: '呈现前清旧条——当前仅一条提示',
+      );
+      ScaffoldMessenger.of(ctx).hideCurrentSnackBar();
+      await tester.pumpAndSettle();
+      expect(
+        find.text(
+          'Already uploaded to this album — tap again to select anyway',
+        ),
+        findsNothing,
+        reason: '隐藏后无第二条在队列等待（不堆积）',
+      );
     });
 
     testWidgets('② 服务器单项命中 → 拒选（单项请求携带 filename+bytes）',
@@ -483,5 +511,94 @@ void main() {
           reason: '取消选择路径不发起任何查询（本机命中也短路服务器）');
       await drainBlockedSnackBar(tester, ctx);
     });
+
+    testWidgets('⑥ 服务器预检超时（注入 50ms 帽）→ 放行（时间帽=无命中）',
+        (tester) async {
+      final session = FakeSessionStore()
+        ..session = Session(
+          token: 'tok-1',
+          expiresAt: DateTime.utc(2099, 1, 1),
+          account: 'alice',
+        );
+      final store = TaskStore.memory();
+      addTearDown(() => store.close());
+      // 永不回包的适配器：请求受理但响应挂起（模拟弱网下预检吊住——
+      // 不等 dio 默认超时，靠注入的短时间帽放行）。
+      final neverResponds = Completer<(int, Object?)>();
+      final adapter = FakeAdapter((o) => neverResponds.future);
+      final client = ApiClient(
+        sessionStore: session,
+        dio: Dio(BaseOptions(baseUrl: 'http://test.local'))
+          ..httpClientAdapter = adapter,
+      );
+
+      late BuildContext ctx;
+      await pumpGateHost(tester, (c) => ctx = c);
+      final gate = PickerDuplicateGate(
+        store: store,
+        client: client,
+        accountId: 'alice',
+        albumId: 'alb-1',
+        serverCheckTimeout: const Duration(milliseconds: 50),
+      );
+
+      late bool verdict;
+      await tester.runAsync(() async {
+        verdict = await gate.decideFact(
+          ctx,
+          gateAsset(bytes: kJpgBytes.length),
+          false,
+        );
+      });
+
+      expect(verdict, isTrue, reason: '超时=无命中 → 放行（绝不吊起点选）');
+      expect(adapter.requests, hasLength(1), reason: '预检确已发出（只是没回）');
+    });
+
+    testWidgets('⑦ fileSize 获取失败 → 放行（预检故障不挡选图）',
+        (tester) async {
+      final session = FakeSessionStore()
+        ..session = Session(
+          token: 'tok-1',
+          expiresAt: DateTime.utc(2099, 1, 1),
+          account: 'alice',
+        );
+      final store = TaskStore.memory();
+      addTearDown(() => store.close());
+      final adapter = FakeAdapter(
+        (o) => (200, {'duplicates': <Map<String, dynamic>>[]}),
+      );
+      final client = ApiClient(
+        sessionStore: session,
+        dio: Dio(BaseOptions(baseUrl: 'http://test.local'))
+          ..httpClientAdapter = adapter,
+      );
+
+      late BuildContext ctx;
+      await pumpGateHost(tester, (c) => ctx = c);
+      final gate = PickerDuplicateGate(
+        store: store,
+        client: client,
+        accountId: 'alice',
+        albumId: 'alb-1',
+      );
+
+      late bool verdict;
+      await tester.runAsync(() async {
+        verdict = await gate.decideFact(
+          ctx,
+          (
+            id: 'asset-1',
+            title: 'pick1.jpg',
+            fileSize: () async => throw StateError('size failed'),
+          ),
+          false,
+        );
+      });
+
+      expect(verdict, isTrue, reason: 'fileSize 失败 → 放行');
+      expect(adapter.requests, isEmpty,
+          reason: 'fileSize 失败短路两半场——不发起任何查询');
+    });
   });
 }