Add Designer copy, cut, paste and duplicate support

ModernFormsNext.Designer.Tests/DesignerRuntimeLayoutParityTests.cs

@@ -185,6 +185,41 @@ public void ChildReorderRemoveAndAddStayEquivalentToRuntimeOrder()
         DesignerRuntimeLayoutParityHarness.AssertParity("order-added", document, document);
     }
 
+    [Theory]
+    [InlineData(1d)]
+    [InlineData(1.25d)]
+    [InlineData(1.5d)]
+    [InlineData(2d)]
+    public void ClipboardPasteAndDuplicateUseProductionLayoutSemanticsAtDpiScale(double dpiScale)
+    {
+        var document = BasicDocument();
+        var source = Node("source", "Panel", 12, 18, 110, 80);
+        source.Properties["Padding"] = PaddingValue(new Padding(3, 5, 7, 9));
+        source.Children.Add(Node("header", "Panel", 0, 0, 30, 24, DockStyle.Top));
+        source.Children.Add(Node("content", "Panel", 0, 0, 30, 30, DockStyle.Fill));
+        var target = Node("target", "Panel", 140, 10, 140, 170);
+        target.Properties["Padding"] = PaddingValue(new Padding(6));
+        document.Controls.Add(source);
+        document.Controls.Add(target);
+        using var session = new DesignerSession();
+        session.LoadDocument(document);
+
+        session.SelectNode(source);
+        Assert.True(session.CopySelectedNode());
+        session.SelectNode(target);
+        Assert.True(session.PasteCopiedNode());
+        Assert.True(session.DuplicateSelectedNode());
+
+        Assert.Equal(2, target.Children.Count);
+        Assert.Equal("source1", target.Children[0].Name);
+        Assert.Equal("source2", target.Children[1].Name);
+        Assert.Equal(new DesignBounds(28, 34, 110, 80), target.Children[0].Bounds);
+        Assert.Equal(new DesignBounds(44, 50, 110, 80), target.Children[1].Bounds);
+        DesignerRuntimeLayoutParityHarness.AssertDpiParity(
+            new ParityScenario($"clipboard-paste-duplicate-{dpiScale:0.##}x", () => document),
+            dpiScale);
+    }
+
     public static IEnumerable<object[]> CoreParityScenarios()
     {
         yield return Scenario("ordinary-child", () => WithChildren(Node("child", "Panel", 17, 23, 91, 47)));

ModernFormsNext.Designer/Clipboard/DesignerClipboard.cs

@@ -0,0 +1,49 @@
+namespace ModernFormsNext.Designer.Clipboard;
+
+/// <summary>
+/// Stores Designer clipboard content without depending on the runtime or operating-system clipboard.
+/// </summary>
+/// <remarks>
+/// Content is an immutable string payload. Keeping the abstraction data-only allows one Designer
+/// session to copy between open documents without retaining controls, selections, histories, or
+/// host services from the source document.
+/// </remarks>
+internal interface IDesignerClipboard
+{
+    event EventHandler? Changed;
+
+    string? Content { get; }
+
+    void SetContent(string content);
+
+    void Clear();
+}
+
+internal sealed class DesignerClipboard : IDesignerClipboard
+{
+    private string? content;
+
+    public event EventHandler? Changed;
+
+    public string? Content => content;
+
+    public void SetContent(string content)
+    {
+        ArgumentException.ThrowIfNullOrWhiteSpace(content);
+
+        if (string.Equals(this.content, content, StringComparison.Ordinal))
+            return;
+
+        this.content = content;
+        Changed?.Invoke(this, EventArgs.Empty);
+    }
+
+    public void Clear()
+    {
+        if (content is null)
+            return;
+
+        content = null;
+        Changed?.Invoke(this, EventArgs.Empty);
+    }
+}

ModernFormsNext.Designer/Clipboard/DesignerClipboardPayload.cs

@@ -0,0 +1,69 @@
+using System.Text.Json.Serialization;
+using ModernFormsNext.Designing;
+
+namespace ModernFormsNext.Designer.Clipboard;
+
+/// <summary>
+/// Defines the private, versioned data contract stored by the Designer clipboard.
+/// </summary>
+/// <remarks>
+/// These DTOs deliberately mirror only persisted design data. They do not contain runtime
+/// controls, CLR type instances, handles, delegates, dispatchers, histories, or selections.
+/// </remarks>
+internal sealed class DesignerClipboardPayload
+{
+    public const string CurrentFormat = "ModernFormsNext.Designer";
+    public const int CurrentVersion = 1;
+
+    public string? Format { get; set; }
+
+    public int? Version { get; set; }
+
+    public DesignerClipboardNode? Root { get; set; }
+}
+
+internal sealed class DesignerClipboardNode
+{
+    public string? TypeName { get; set; }
+
+    public string? Name { get; set; }
+
+    public int? X { get; set; }
+
+    public int? Y { get; set; }
+
+    public int? Width { get; set; }
+
+    public int? Height { get; set; }
+
+    public DesignerMemberVisibility? MemberVisibility { get; set; }
+
+    public SortedDictionary<string, DesignerClipboardValue>? Properties { get; set; }
+
+    public SortedDictionary<string, string?>? Events { get; set; }
+
+    public List<DesignerClipboardNode>? Children { get; set; }
+}
+
+internal sealed class DesignerClipboardValue
+{
+    public DesignPropertyValueKind? Kind { get; set; }
+
+    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
+    public string? StringValue { get; set; }
+
+    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
+    public bool? BooleanValue { get; set; }
+
+    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
+    public int? Int32Value { get; set; }
+
+    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
+    public double? DoubleValue { get; set; }
+
+    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
+    public string? TypeName { get; set; }
+
+    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
+    public SortedDictionary<string, DesignerClipboardValue>? Properties { get; set; }
+}