feat(ui): port retained widget foundations

tests/AcDream.App.Tests/UI/UiRootInputTests.cs

@@ -482,4 +482,99 @@ public class UiRootInputTests
         Assert.True(clicked.ZOrder > peer.ZOrder);
         root.OnMouseUp(UiMouseButton.Left, 50, 50);
     }
+
+    [Fact]
+    public void AddChild_AssignsEventIdsRecursively()
+    {
+        var root = new UiRoot { Width = 800, Height = 600 };
+        var parent = new UiPanel { Width = 100, Height = 100 };
+        var child = new UiPanel { Width = 50, Height = 50 };
+        var grandchild = new UiPanel { Width = 25, Height = 25 };
+        child.AddChild(grandchild);
+        parent.AddChild(child);
+
+        root.AddChild(parent);
+
+        Assert.NotEqual(0u, parent.EventId);
+        Assert.NotEqual(0u, child.EventId);
+        Assert.NotEqual(0u, grandchild.EventId);
+        Assert.Equal(3, new[] { parent.EventId, child.EventId, grandchild.EventId }.Distinct().Count());
+    }
+
+    [Fact]
+    public void RemovingSubtree_ClearsAllRootOwnership()
+    {
+        var root = new UiRoot { Width = 800, Height = 600 };
+        var window = new UiPanel { Width = 200, Height = 100 };
+        var field = new UiField { Width = 100, Height = 20 };
+        window.AddChild(field);
+        root.AddChild(window);
+        root.RegisterWindow("test", window);
+        root.DefaultTextInput = field;
+        root.Modal = window;
+        root.SetKeyboardFocus(field);
+        root.SetCapture(field);
+
+        Assert.True(root.RemoveChild(window));
+
+        Assert.Null(root.KeyboardFocus);
+        Assert.Null(root.Captured);
+        Assert.Null(root.DefaultTextInput);
+        Assert.Null(root.Modal);
+        Assert.False(root.ShowWindow("test"));
+    }
+
+    [Fact]
+    public void Tick_ChecksTooltipBeforeGlobalTimeMessage_AtRetailDelay()
+    {
+        var root = new UiRoot { Width = 800, Height = 600 };
+        var recorder = new TimeOrderRecorder { Width = 100, Height = 100 };
+        root.AddChild(recorder);
+
+        root.Tick(0, 1_000);
+        root.OnMouseMove(10, 10);
+        recorder.Events.Clear();
+        root.Tick(0, 1_249);
+        Assert.DoesNotContain("tooltip", recorder.Events);
+        recorder.Events.Clear();
+
+        root.Tick(0, 1_250);
+
+        Assert.Equal(new[] { "tooltip", "global" }, recorder.Events);
+    }
+
+    [Fact]
+    public void Tick_GlobalTimeRemoval_SkipsDetachedSiblingWithoutInvalidatingWalk()
+    {
+        var root = new UiRoot { Width = 800, Height = 600 };
+        var victim = new TimeOrderRecorder { Width = 100, Height = 100 };
+        var remover = new GlobalTimeAction(() => root.RemoveChild(victim))
+            { Width = 100, Height = 100 };
+        root.AddChild(remover);
+        root.AddChild(victim);
+
+        root.Tick(0, 1_000);
+
+        Assert.Empty(victim.Events);
+        Assert.Null(victim.Parent);
+    }
+
+    private sealed class TimeOrderRecorder : UiElement, IUiGlobalTimeListener
+    {
+        public List<string> Events { get; } = new();
+
+        public override bool OnEvent(in UiEvent e)
+        {
+            if (e.Type != UiEventType.Tooltip) return false;
+            Events.Add("tooltip");
+            return true;
+        }
+
+        public void OnGlobalUiTime(double nowSeconds) => Events.Add("global");
+    }
+
+    private sealed class GlobalTimeAction(Action action) : UiElement, IUiGlobalTimeListener
+    {
+        public void OnGlobalUiTime(double nowSeconds) => action();
+    }
 }