fix(uwp): make BakedAspectGraph compile under .NET Native

Four fixes restore the UWP build the v0.6.0 release surfaced as broken:

- Switch CompositionExpressions from a sibling-repo ProjectReference
  to a NuGet PackageReference (arcadiog.CompositionExpressions 0.1.3,
  newly published from the CompositionCollectionView repo with a UWP
  flavour). Both Combobulate.csproj and Combobulate.WinAppSdk.csproj
  consume the same package now; CI no longer needs to find a sibling
  checkout.
- Add the BAG sources (AspectGraphBake, BakedAspectGraphRenderer,
  EventFunctions, PredicateCompiler, SignatureBake, TransformAnimationAxis)
  to Combobulate.csproj's explicit Compile list so the UWP target
  actually compiles them. Add #if WINAPPSDK around Microsoft.UI.Composition
  / Microsoft.UI.Dispatching usings, with Windows.UI.Composition /
  Windows.System fallbacks aliased via DispatcherQueueNS.
- Replace VisualCollection.Contains (a LINQ extension that fails to
  resolve once System.Memory is referenced and pulls a colliding
  MemoryExtensions.Contains overload into scope) with a Visual.Parent
  null-check.
- Move IFaceSorter.CullEpsilon onto FaceSorterFactory: an interface
  const requires default-interface-implementation support which UWP's
  .NET Native runtime rejects with CS8701. Update the one test that
  read the const accordingly.
- Add a System.Memory PackageReference to the UWP csproj so Span<T>
  resolves (PolygonSplitter and NewellSorter use Span).

Author: arcadiogarcia

src/Combobulate.WinAppSdk/Combobulate.WinAppSdk.csproj

@@ -22,16 +22,13 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.WindowsAppSDK" Version="1.7.250401001" />
+    <PackageReference Include="arcadiog.CompositionExpressions" Version="0.1.3" />
     <PackageReference Include="PolySharp" Version="1.14.1">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
     </PackageReference>
   </ItemGroup>
 
-  <ItemGroup>
-    <ProjectReference Include="..\..\..\CompositionCollectionView\src\CompositionExpressions.WinAppSdk\CompositionExpressions.WinAppSdk.csproj" />
-  </ItemGroup>
-
   <!-- Shared source files from the UWP library project -->
   <ItemGroup>
     <Compile Include="..\Combobulate\**\*.cs"

src/Combobulate/Combobulate.csproj

@@ -177,6 +177,12 @@
     <PackageReference Include="Microsoft.NETCore.UniversalWindowsPlatform">
       <Version>6.2.14</Version>
     </PackageReference>
+    <PackageReference Include="System.Memory">
+      <Version>4.5.5</Version>
+    </PackageReference>
+    <PackageReference Include="arcadiog.CompositionExpressions">
+      <Version>0.1.3</Version>
+    </PackageReference>
     <PackageReference Include="PolySharp" Version="1.14.1">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>

src/Combobulate/Rendering/BakedAspectGraphRenderer.cs

@@ -744,7 +744,7 @@ private void EvictStaging()
         {
             try
             {
-                if (_parent.Children.Contains(t)) _parent.Children.Remove(t);
+                if (t.Parent != null) _parent.Children.Remove(t);
                 t.Dispose();
             }
             catch { }
@@ -759,7 +759,7 @@ private void DisposeTrees()
         {
             t.StopAnimation("Opacity");
             t.Children.RemoveAll();
-            if (_parent.Children.Contains(t)) _parent.Children.Remove(t);
+            if (t.Parent != null) _parent.Children.Remove(t);
             t.Dispose();
         }
         _trees = null;

src/Combobulate/Sorting/IFaceSorter.cs

@@ -26,17 +26,6 @@ namespace Combobulate.Sorting;
 /// </summary>
 public interface IFaceSorter
 {
-    /// <summary>
-    /// Back-face cull threshold. Re-exports
-    /// <see cref="GeometryPredicates.CosineEpsilon"/> so existing call
-    /// sites and tests that reference <c>IFaceSorter.CullEpsilon</c>
-    /// continue to work; new code should prefer
-    /// <see cref="GeometryPredicates.IsFrontFacing"/> directly.
-    ///
-    /// <para>See <see cref="GeometryPredicates"/> for the full epsilon
-    /// hierarchy (cosine / distance / divisor / squared-length scales).</para>
-    /// </summary>
-    public const float CullEpsilon = GeometryPredicates.CosineEpsilon;
     /// <summary>
     /// Number of source quads this sorter was built for. The caller's
     /// <paramref name="orderBuffer"/> and <paramref name="visibleBuffer"/>
@@ -78,6 +67,20 @@ public interface IFaceSorter
 /// </summary>
 public static class FaceSorterFactory
 {
+    /// <summary>
+    /// Back-face cull threshold. Re-exports
+    /// <see cref="GeometryPredicates.CosineEpsilon"/> so existing call
+    /// sites and tests that reference <c>FaceSorterFactory.CullEpsilon</c>
+    /// keep working; new code should prefer
+    /// <see cref="GeometryPredicates.IsFrontFacing"/> directly.
+    ///
+    /// <para>Lives on this static class rather than <see cref="IFaceSorter"/>
+    /// because UWP's .NET Native runtime doesn't support the default-interface-
+    /// implementation feature (CS8701) needed for a const member on an
+    /// interface.</para>
+    /// </summary>
+    public const float CullEpsilon = GeometryPredicates.CosineEpsilon;
+
     public static IFaceSorter Create(SortAlgorithm algorithm, ObjGeometry geometry)
     {
         return algorithm switch

tests/Combobulate.Tests/Sorting/CullEpsilonTests.cs

@@ -82,8 +82,8 @@ public void GenuinelyVisibleQuadAtYaw89_IsRendered(SortAlgorithm algo)
     public void CullEpsilonIsPositiveAndAboveSinglePrecisionCosNoise()
     {
         // The whole point: must be > the noise floor of MathF.Cos(MathF.PI/2).
-        Assert.True(IFaceSorter.CullEpsilon > 1e-6f, "Epsilon too tight; fp noise will leak through");
-        Assert.True(IFaceSorter.CullEpsilon < 1e-2f, "Epsilon too loose; legitimate near-edge-on faces would be culled");
+        Assert.True(FaceSorterFactory.CullEpsilon > 1e-6f, "Epsilon too tight; fp noise will leak through");
+        Assert.True(FaceSorterFactory.CullEpsilon < 1e-2f, "Epsilon too loose; legitimate near-edge-on faces would be culled");
     }
 
     /// <summary>