fix: wire backend<->engine data flow so content renders and input works

desktop/integration_test/e2e_test.dart

@@ -1,11 +1,14 @@
 // 端到端集成测试：在真实 Windows 桌面运行完整链路。
 //
 // 验证：RustLib.init() → 点 CONNECT → TerminalEngine（Alacritty Rust 引擎）创建
-// → 连上服务端 → 命令回显。
+// → 连上服务端 → 命令回显（内容渲染 + 输入通路）。
 //
 // 运行前需先启动 Rust 服务端（cd .. && cargo run）。
 // 运行：flutter test integration_test -d windows
-import 'package:flutter/material.dart';
+import 'dart:async';
+import 'dart:typed_data';
+
+import 'package:flutter/foundation.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter_alacritty/flutter_alacritty.dart';
 import 'package:integration_test/integration_test.dart';
@@ -33,15 +36,48 @@ void main() {
       await tester.pump(const Duration(milliseconds: 200));
       if (find.text('AWAITING CONNECTION').evaluate().isEmpty) break;
     }
-
     expect(find.text('AWAITING CONNECTION'), findsNothing,
-        reason: '连接后应进入终端渲染，提示页应消失');
+        reason: '连接后应进入终端渲染');
 
-    // TerminalView（Alacritty 引擎渲染）应存在。
+    // Alacritty TerminalView 应渲染。
     expect(find.byType(TerminalView), findsOneWidget,
         reason: 'Alacritty TerminalView 应渲染');
 
-    // 断言 TerminalScreen 仍在前台。
+    // 通过引擎输出通路发送一条命令（模拟用户输入），验证：
+    // 服务端回显 → backend.output → engine.feed → 网格渲染。
+    final engine = tester.state<TerminalViewState>(find.byType(TerminalView)).widget.engine;
+    final token = 'RTTY_INT_${DateTime.now().millisecondsSinceEpoch}';
+    engine.write(Uint8List.fromList('echo $token\r\n'.codeUnits));
+
+    // 轮询引擎网格，等待命令回显进入渲染。
+    String? found;
+    final outDeadline = DateTime.now().add(const Duration(seconds: 8));
+    while (DateTime.now().isBefore(outDeadline)) {
+      await tester.pump(const Duration(milliseconds: 200));
+      final gridText = _gridText(engine);
+      if (gridText.contains(token)) {
+        found = gridText;
+        break;
+      }
+    }
+    expect(found, isNotNull, reason: '命令回显应进入引擎网格');
+    debugPrint('回显捕获: ${found!.trim().split('\n').last}');
+
+    // 输入通路也验证：TerminalView 聚焦时按键应经 engine.write → backend → 服务端。
     expect(find.byType(TerminalScreen), findsOneWidget);
   });
 }
+
+/// 从引擎镜像网格提取可视文本。
+String _gridText(TerminalEngine engine) {
+  final grid = engine.gridForView;
+  final sb = StringBuffer();
+  for (var r = 0; r < grid.rows; r++) {
+    for (var c = 0; c < grid.columns; c++) {
+      final cp = grid.codepointAt(r, c) as int;
+      sb.writeCharCode(cp == 0 ? 32 : cp);
+    }
+    sb.write('\n');
+  }
+  return sb.toString();
+}

desktop/lib/src/terminal_screen.dart

@@ -1,3 +1,6 @@
+import 'dart:async';
+import 'dart:typed_data';
+
 import 'package:flutter/material.dart';
 import 'package:flutter_alacritty/flutter_alacritty.dart';
 
@@ -25,6 +28,8 @@ class _TerminalScreenState extends State<TerminalScreen> {
   final FocusNode _focus = FocusNode();
 
   RttyPtyBackend? _backend;
+  StreamSubscription<Uint8List>? _engineOutputSub;
+  StreamSubscription<Uint8List>? _backendOutputSub;
 
   final _host = TextEditingController(text: '127.0.0.1');
   final _port = TextEditingController(text: '8080');
@@ -66,14 +71,22 @@ class _TerminalScreenState extends State<TerminalScreen> {
       _backend = RttyPtyBackend();
     });
 
-    _backend!.onStateChanged = (s) {
+    final engine = _engine!;
+    final backend = _backend!;
+
+    // 双向接线：backend 输出（服务端 ANSI）→ 引擎渲染；
+    // 引擎输出（用户输入）→ backend 发回服务端写入远端 PTY。
+    _engineOutputSub = engine.output.listen(backend.write);
+    _backendOutputSub = backend.output.listen(engine.feed);
+
+    backend.onStateChanged = (s) {
       if (!mounted) return;
       setState(() => _state = s);
       if (s == ConnState.disconnected || s == ConnState.error) {
         _sessionId = null;
       }
     };
-    _backend!.onReady = (id, cols, rows) {
+    backend.onReady = (id, cols, rows) {
       if (!mounted) return;
       setState(() {
         _sessionId = id;
@@ -82,12 +95,17 @@ class _TerminalScreenState extends State<TerminalScreen> {
       });
     };
 
-    await _backend!.connect(host: host, port: port, session: session);
+    await backend.connect(host: host, port: port, session: session);
   }
 
   void _disconnect() => _tearDownSession();
 
   void _tearDownSession() {
+    _engineOutputSub?.cancel();
+    _engineOutputSub = null;
+    _backendOutputSub?.cancel();
+    _backendOutputSub = null;
+
     final b = _backend;
     if (b != null) {
       b.onStateChanged = null;