Fix button auto-size text measurement

Lessons.md

@@ -22,6 +22,7 @@
 - Treat screenshot-reported UI precision bugs as shared geometry suspects first. Hit testing, caret placement, slider bounds, and popup placement usually belong in shared measurement, transform, bounds, or z-layer code rather than one-off component fixes.
 - Keep the UI A/B sample useful as a validation tool, not just a showcase. Add visible state, labels, and layout previews when controls otherwise look inert or ambiguous.
 - For retained text input, caret, selection, and scrolling should share measured text advances. Any fallback heuristic must be treated as a temporary approximation and tested against proportional text.
+- For retained UI controls that render text with measured glyph widths, auto-size measurement should use the same measured text path. Character-count heuristics are only safe as fallbacks when no render measurement context is available.
 
 ## PR Review And Triage
 

src/ModernOverlay.UI/Controls.cs

@@ -553,11 +553,17 @@ protected override SizeF MeasureCore(SizeF availableSize)
         }
 
         float fontSize = Root?.ThemeResources.Theme.FontSize ?? UiTheme.Default.FontSize;
-        float width = MathF.Min(availableSize.Width, Text.Length * fontSize * 0.6f + Padding.Horizontal);
-        float height = fontSize * 1.35f + Padding.Vertical;
+        SizeF textSize = MeasureButtonText(Text, fontSize);
+        float width = MathF.Min(availableSize.Width, textSize.Width + Padding.Horizontal);
+        float height = textSize.Height * 1.35f + Padding.Vertical;
         return new SizeF(MathF.Max(MinWidth, width), MathF.Max(MinHeight, height));
     }
 
+    private SizeF MeasureButtonText(string value, float fontSize)
+        => Root is { } root && root.TryMeasureText(value, root.ThemeResources.Font, out SizeF measured)
+            ? measured
+            : new SizeF(value.Length * fontSize * 0.6f, fontSize);
+
     protected override void ArrangeCore(RectF finalRect)
     {
         ArrangeContent();

tests/ModernOverlay.Tests/OverlayUiButtonControlTests.cs

@@ -153,6 +153,29 @@ public async Task ButtonTextAlignmentControlsTextOrigin()
         Assert.AreEqual(left.ContentBounds.X, leftOrigin.X, 0.001f);
     }
 
+    [TestMethod]
+    [TestCategory("WindowsIntegration")]
+    public async Task ButtonAutoSizeUsesMeasuredTextWidth()
+    {
+        await using OverlayWindow overlay = await CreateOverlayAsync();
+        using OverlayUiRoot ui = OverlayUi.Attach(overlay, new OverlayUiOptions { RegisterInputRegions = false });
+        UiButton button = new()
+        {
+            Text = "WWW",
+            Height = 28f,
+            HorizontalAlignment = UiHorizontalAlignment.Left,
+            VerticalAlignment = UiVerticalAlignment.Top,
+        };
+        Canvas.SetLeft(button, 10f);
+        Canvas.SetTop(button, 10f);
+        ui.Root.Children.Add(button);
+
+        ui.Render(new DrawContext(new RecordingDrawCommandSink()));
+
+        Assert.AreEqual(140f, button.DesiredSize.Width, 0.001f);
+        Assert.AreEqual(140f, button.Bounds.Width, 0.001f);
+    }
+
     [TestMethod]
     [TestCategory("WindowsIntegration")]
     public async Task RadioButtonClearsPeersAndHonorsDisabledDynamicGroupChanges()
@@ -336,7 +359,9 @@ public void DrawTextLayout(TextLayoutHandle layout, BrushHandle brush, PointF or
             => AddPrimitive();
 
         public SizeF MeasureText(string text, FontHandle font)
-            => new(text.Length, font.Options.Size);
+            => text == "WWW"
+                ? new SizeF(120f, font.Options.Size)
+                : new SizeF(text.Length, font.Options.Size);
 
         public SizeF MeasureTextLayout(TextLayoutHandle layout)
             => new(layout.Text.Length, layout.Font.Options.Size);