第 0 阶段：教材项目 2 任务 1 在网页中原样运行

- runtime：仿真 WinForms 子集（Form、Button、Label、TextBox、ComboBox、
  GroupBox、Timer、MessageBox、界面线程消息循环、跨线程检查）、
  教材设备类库（DeviceCtrlHelper、LED 控件）、运行器（常驻编译服务 + 运行模式）
- server：Bun + Hono，WebSocket 会话，每次运行一个进程，消息转发
- web：Vue + Naive UI，WinForms 风格窗体渲染、MessageBox、实训台 LED 屏
- 端到端测试与 100 个程序并发的压力测试
- 教材逐任务摘要（docs/教材摘要）

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

runtime/Sim.WinForms/Forms/ComboBox.cs

@@ -0,0 +1,176 @@
+using System.Collections;
+using System.Collections.Generic;
+using System.Drawing;
+using System.Linq;
+using System.Text.Json.Nodes;
+using Sim.Host;
+
+namespace System.Windows.Forms;
+
+public class ComboBox : Control
+{
+    private int _selectedIndex = -1;
+    private ComboBoxStyle _dropDownStyle = ComboBoxStyle.DropDown;
+
+    public ComboBox() => Items = new ObjectCollection(this);
+
+    protected override Size DefaultSize => new(121, 20);
+
+    public ObjectCollection Items { get; }
+
+    public bool FormattingEnabled { get; set; }
+    public int MaxDropDownItems { get; set; } = 8;
+    public int DropDownWidth { get; set; } = 121;
+    public int DropDownHeight { get; set; } = 106;
+    public bool Sorted { get; set; }
+    public bool DroppedDown { get; set; }
+
+    public ComboBoxStyle DropDownStyle
+    {
+        get => _dropDownStyle;
+        set => SetProp(ref _dropDownStyle, value, nameof(DropDownStyle));
+    }
+
+    public int SelectedIndex
+    {
+        get => _selectedIndex;
+        set
+        {
+            if (value < -1 || value >= Items.Count)
+                throw new ArgumentOutOfRangeException(nameof(value), $"“{value}”的值对于“SelectedIndex”无效。");
+            if (value == _selectedIndex) return;
+            SetProp(ref _selectedIndex, value, nameof(SelectedIndex));
+            // 选中项变化时 Text 随之变化（先 TextChanged，再 SelectedIndexChanged，与 WinForms 一致）
+            Text = value >= 0 ? Items[value]?.ToString() ?? "" : "";
+            OnSelectedIndexChanged(EventArgs.Empty);
+            OnSelectedValueChanged(EventArgs.Empty);
+        }
+    }
+
+    public object? SelectedItem
+    {
+        get => _selectedIndex >= 0 ? Items[_selectedIndex] : null;
+        set => SelectedIndex = value == null ? -1 : Items.IndexOf(value);
+    }
+
+    public string SelectedText { get; set; } = "";
+
+    public event EventHandler? SelectedIndexChanged;
+    public event EventHandler? SelectedValueChanged;
+    public event EventHandler? DropDown;
+    public event EventHandler? DropDownClosed;
+
+    protected virtual void OnSelectedIndexChanged(EventArgs e) => SelectedIndexChanged?.Invoke(this, e);
+    protected virtual void OnSelectedValueChanged(EventArgs e) => SelectedValueChanged?.Invoke(this, e);
+    protected virtual void OnDropDown(EventArgs e) => DropDown?.Invoke(this, e);
+    protected virtual void OnDropDownClosed(EventArgs e) => DropDownClosed?.Invoke(this, e);
+
+    public void BeginUpdate() { }
+    public void EndUpdate() { }
+
+    protected override void OnUserAction(UserAction action)
+    {
+        switch (action.Action)
+        {
+            case "dropDown":
+                // 教材在 Click 事件里刷新串口列表，所以 Click 必须在列表展开之前触发
+                OnClick(EventArgs.Empty);
+                OnDropDown(EventArgs.Empty);
+                break;
+            case "select":
+                if (action.Index >= 0 && action.Index < Items.Count) SelectedIndex = action.Index;
+                OnDropDownClosed(EventArgs.Empty);
+                break;
+            case "text" when _dropDownStyle != ComboBoxStyle.DropDownList:
+                SetTextFromUser(action.Value ?? "");
+                var match = Items.IndexOf(Text);
+                if (match != _selectedIndex) _selectedIndex = match;
+                break;
+            default:
+                base.OnUserAction(action);
+                break;
+        }
+    }
+
+    internal void ItemsChanged()
+    {
+        if (_selectedIndex >= Items.Count) _selectedIndex = -1;
+        NotifyChanged(nameof(Items), Items.Select(i => i?.ToString() ?? "").ToArray());
+    }
+
+    protected override void WriteProps(JsonObject props)
+    {
+        base.WriteProps(props);
+        props["Items"] = PropValue.From(Items.Select(i => i?.ToString() ?? "").ToArray());
+        props["SelectedIndex"] = _selectedIndex;
+        props["DropDownStyle"] = _dropDownStyle.ToString();
+    }
+
+    public class ObjectCollection : IList, IEnumerable<object?>
+    {
+        private readonly List<object?> _items = new();
+        private readonly ComboBox _owner;
+
+        public ObjectCollection(ComboBox owner) => _owner = owner;
+
+        public int Count => _items.Count;
+        public bool IsReadOnly => false;
+        bool IList.IsFixedSize => false;
+        bool ICollection.IsSynchronized => false;
+        object ICollection.SyncRoot => this;
+
+        public object? this[int index]
+        {
+            get => _items[index];
+            set
+            {
+                _items[index] = value;
+                _owner.ItemsChanged();
+            }
+        }
+
+        public int Add(object? item)
+        {
+            if (item == null) throw new ArgumentNullException(nameof(item), "值不能为 null。");
+            _items.Add(item);
+            _owner.ItemsChanged();
+            return _items.Count - 1;
+        }
+
+        public void AddRange(object[] items)
+        {
+            _items.AddRange(items);
+            _owner.ItemsChanged();
+        }
+
+        public void Insert(int index, object? item)
+        {
+            _items.Insert(index, item);
+            _owner.ItemsChanged();
+        }
+
+        public void Remove(object? item)
+        {
+            if (_items.Remove(item)) _owner.ItemsChanged();
+        }
+
+        public void RemoveAt(int index)
+        {
+            _items.RemoveAt(index);
+            _owner.ItemsChanged();
+        }
+
+        public void Clear()
+        {
+            _items.Clear();
+            _owner.SelectedIndex = -1;
+            _owner.ItemsChanged();
+        }
+
+        public bool Contains(object? item) => _items.Contains(item);
+        public int IndexOf(object? item) => _items.IndexOf(item);
+        public void CopyTo(Array array, int index) => ((ICollection)_items).CopyTo(array, index);
+        public IEnumerator<object?> GetEnumerator() => _items.GetEnumerator();
+        IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
+    }
+}