perf(ui): retain shaped report text

tests/AcDream.App.Tests/UI/Layout/UiTextLayoutCacheTests.cs

@@ -0,0 +1,79 @@
+using AcDream.App.UI;
+using AcDream.App.UI.Layout;
+
+namespace AcDream.App.Tests.UI.Layout;
+
+public sealed class UiTextLayoutCacheTests
+{
+    [Fact]
+    public void Stable_content_and_layout_borrow_same_shaped_lines()
+    {
+        var text = new UiText { Width = 120f };
+        int shapes = 0;
+        var cache = new UiTextLayoutCache<string>(
+            text,
+            (target, value) =>
+            {
+                shapes++;
+                return IndicatorDetailText.Shape(target, value);
+            },
+            "alpha beta gamma",
+            StringComparer.Ordinal);
+
+        IReadOnlyList<UiText.Line> first = cache.GetLines();
+        IReadOnlyList<UiText.Line> second = cache.GetLines();
+
+        Assert.Same(first, second);
+        Assert.Equal(1, shapes);
+
+        cache.SetValue(new string("alpha beta gamma".ToCharArray()));
+        Assert.Same(first, cache.GetLines());
+        Assert.Equal(1, shapes);
+    }
+
+    [Fact]
+    public void Content_width_and_font_inputs_invalidate_shaping()
+    {
+        var text = new UiText { Width = 120f };
+        int shapes = 0;
+        var cache = new UiTextLayoutCache<string>(
+            text,
+            (target, value) =>
+            {
+                shapes++;
+                return IndicatorDetailText.Shape(target, value);
+            },
+            "alpha beta gamma",
+            StringComparer.Ordinal);
+
+        IReadOnlyList<UiText.Line> first = cache.GetLines();
+        cache.SetValue("delta epsilon");
+        IReadOnlyList<UiText.Line> changed = cache.GetLines();
+        text.Width = 48f;
+        IReadOnlyList<UiText.Line> resized = cache.GetLines();
+
+        Assert.NotSame(first, changed);
+        Assert.NotSame(changed, resized);
+        Assert.Equal(3, shapes);
+    }
+
+    [Fact]
+    public void Stable_provider_poll_allocates_no_managed_memory()
+    {
+        var text = new UiText { Width = 120f };
+        var cache = new UiTextLayoutCache<string>(
+            text,
+            static (target, value) => IndicatorDetailText.Shape(target, value),
+            "alpha beta gamma",
+            StringComparer.Ordinal);
+        Func<IReadOnlyList<UiText.Line>> provider = cache.Provider;
+        _ = provider();
+
+        long before = GC.GetAllocatedBytesForCurrentThread();
+        for (int i = 0; i < 1_000; i++)
+            _ = provider();
+        long allocated = GC.GetAllocatedBytesForCurrentThread() - before;
+
+        Assert.Equal(0L, allocated);
+    }
+}