diff --git a/Directory.Build.props b/Directory.Build.props
index d72190272..fef8d15b9 100644
--- a/Directory.Build.props
+++ b/Directory.Build.props
@@ -1,13 +1,46 @@
 <Project>
 
   <!--
-    Centralize the Windows App SDK version so all projects stay in sync.
+    Centralize the Windows App SDK + CsWinRT versions so all projects stay in sync.
     This uses the public Microsoft.WindowsAppSDK package from NuGet.
     To install: dotnet restore (NuGet will pull the package automatically).
   -->
   <PropertyGroup>
     <WindowsAppSDKVersion>2.0.1</WindowsAppSDKVersion>
     <WindowsAppSDKSelfContained>true</WindowsAppSDKSelfContained>
+    <!-- CsWinRT pin. Latest 2.3.x is currently a prerelease; bump to the next
+         stable when it ships. The PackageReference is added in
+         Directory.Build.targets for any project that opts into WinUI. -->
+    <CsWinRTVersion>2.3.0-prerelease.251115.2</CsWinRTVersion>
+  </PropertyGroup>
+
+  <!-- ──────────────────────────────────────────────────────────────────
+       CsWinRT best-practice defaults for WinUI projects.
+
+       Modeled on OSClient's UES.Common.CSharp.SDK.props
+       (microsoft.visualstudio.com/OS — Build/MSBuild/UES.Common.CSharp.SDK.props),
+       trimmed to the settings that make sense for a pure WinAppSDK repo
+       (no UWP, no OS XAML mixing, no AOT-merged WinRT components).
+
+       Gated on UseWinUI=true so analyzers/source-generators/etc that don't
+       reference WinAppSDK keep their default behavior.
+       ────────────────────────────────────────────────────────────────── -->
+  <PropertyGroup Condition="'$(UseWinUI)' == 'true'">
+    <!-- Get verbose CsWinRT diagnostics in the build log — same default OSClient uses. -->
+    <CsWinRTEnableLogging>true</CsWinRTEnableLogging>
+
+    <!-- We don't author WinRT projections in this repo (we only consume them).
+         IID patching adds startup cost for projection authors and is not needed
+         for consumers. -->
+    <CsWinRTIIDOptimizerOptOut>true</CsWinRTIIDOptimizerOptOut>
+
+    <!-- Don't pick up a side-by-side UWP toolset that may exist on a dev box.
+         Keeps local builds matching what the CI/lab build will produce. -->
+    <CsWinRTUseEnvironmentalTools>false</CsWinRTUseEnvironmentalTools>
+
+    <!-- By default CsWinRT loads WinRT components into a separate AssemblyLoadContext,
+         which breaks JIT-only test/sample apps. Production AOT builds aren't affected. -->
+    <CsWinRTLoadComponentsInDefaultALC>true</CsWinRTLoadComponentsInDefaultALC>
   </PropertyGroup>
 
   <!-- Default Platform to the current machine architecture so that
diff --git a/Directory.Build.targets b/Directory.Build.targets
index 6089a4ff4..5d8764bab 100644
--- a/Directory.Build.targets
+++ b/Directory.Build.targets
@@ -28,4 +28,20 @@
     <PublishAot>false</PublishAot>
   </PropertyGroup>
 
+  <!-- ───────────────────────────────────────────────────────────────────
+       Pin Microsoft.Windows.CsWinRT to the version centralized in
+       $(CsWinRTVersion) (Directory.Build.props). Without this the version
+       floats with whatever WinAppSDK pulls in transitively — currently a
+       very old 2.0.x — and we lose access to newer projection generators
+       and analyzer rules.
+
+       PrivateAssets=all because CsWinRT is a build-time generator; the
+       downstream nupkg should not list it as a dependency.
+       ─────────────────────────────────────────────────────────────────── -->
+  <ItemGroup Condition="'$(UseWinUI)' == 'true'">
+    <PackageReference Include="Microsoft.Windows.CsWinRT"
+                      Version="$(CsWinRTVersion)"
+                      PrivateAssets="all" />
+  </ItemGroup>
+
 </Project>
diff --git a/samples/Reactor.TestApp/Demos/SpecializedEditorsDemo.cs b/samples/Reactor.TestApp/Demos/SpecializedEditorsDemo.cs
index 5be3eacf8..a491e427f 100644
--- a/samples/Reactor.TestApp/Demos/SpecializedEditorsDemo.cs
+++ b/samples/Reactor.TestApp/Demos/SpecializedEditorsDemo.cs
@@ -252,7 +252,7 @@ static FieldDescriptor[] BuildExplicitColumns() =>
         // Explicit: only offer three of the four enum values here.
         TypedColumns.ComboBoxColumn<Gizmo, GizmoPriority>(
             "Priority", g => g.Priority,
-            choices: [GizmoPriority.Low, GizmoPriority.Medium, GizmoPriority.High],
+            choices: (GizmoPriority[])[GizmoPriority.Low, GizmoPriority.Medium, GizmoPriority.High],
             width: 110),
         TypedColumns.HyperlinkColumn<Gizmo>("Website", g => g.Website, width: 200),
         TypedColumns.ColorColumn<Gizmo>("AccentColor", g => g.AccentColor,
diff --git a/samples/ReactorCharting.Gallery/Samples/CandlestickChart.cs b/samples/ReactorCharting.Gallery/Samples/CandlestickChart.cs
index 59848e8f2..43a0aae34 100644
--- a/samples/ReactorCharting.Gallery/Samples/CandlestickChart.cs
+++ b/samples/ReactorCharting.Gallery/Samples/CandlestickChart.cs
@@ -98,7 +98,7 @@ .. D3Axes(xs, ys, left, top, width, height),
              .. Enumerable.Range(0, 4).Select(n => n * 5)
                  .Select(i => D3Charts.Text(xs.Map(i) - 12, top + height + 4, $"Day {i + 1}", 10, ChartMutedForeground)),
              D3Charts.Text(2, top - 14, "Price", 11, ChartMutedForeground),
-             .. D3Legend(left + width - 120, top + 5, [("Bullish", bullBrush), ("Bearish", bearBrush)])]
+             .. D3Legend(left + width - 120, top + 5, ((string, Microsoft.UI.Xaml.Media.SolidColorBrush)[])[("Bullish", bullBrush), ("Bearish", bearBrush)])]
         )
             .AutomationName("Stock Price Candlestick Chart")
             .FullDescription("Candlestick chart showing 20 trading days of OHLC price data, with green candles for bullish and red for bearish days.");
diff --git a/samples/ReactorCharting.Gallery/Samples/CirclePacking.cs b/samples/ReactorCharting.Gallery/Samples/CirclePacking.cs
index 048b0f7c2..7af8f3947 100644
--- a/samples/ReactorCharting.Gallery/Samples/CirclePacking.cs
+++ b/samples/ReactorCharting.Gallery/Samples/CirclePacking.cs
@@ -106,7 +106,7 @@ .. allNodes.SelectMany(node =>
                         };
                     }
 
-                    return [circle];
+                    return (Element[])[circle];
                 }
                 else
                 {
diff --git a/samples/ReactorCharting.Gallery/Samples/DifferenceChart.cs b/samples/ReactorCharting.Gallery/Samples/DifferenceChart.cs
index 90794a441..0cb5e03c3 100644
--- a/samples/ReactorCharting.Gallery/Samples/DifferenceChart.cs
+++ b/samples/ReactorCharting.Gallery/Samples/DifferenceChart.cs
@@ -85,7 +85,7 @@ public override Element Render()
                 stroke: greenBrush, strokeWidth: 2, curve: D3Curve.MonotoneX),
             D3LinePath(data, x: d => xScale.Map(d.X), y: d => yScale.Map(d.B),
                 stroke: redBrush, strokeWidth: 2, curve: D3Curve.MonotoneX),
-            .. D3Legend(lx, marginTop + 6, [("Revenue", greenBrush), ("Expenses", redBrush)]),
+            .. D3Legend(lx, marginTop + 6, ((string, Microsoft.UI.Xaml.Media.SolidColorBrush)[])[("Revenue", greenBrush), ("Expenses", redBrush)]),
             Microsoft.UI.Reactor.Charting.D3Charts.Text(marginLeft, 4, "Difference Chart (Revenue vs Expenses)", 14, ChartForeground),
         ])
             .AutomationName("Difference Chart (Revenue vs Expenses)")
diff --git a/samples/ReactorCharting.Gallery/Samples/DivergingBarChart.cs b/samples/ReactorCharting.Gallery/Samples/DivergingBarChart.cs
index b8d628646..aecc1e81c 100644
--- a/samples/ReactorCharting.Gallery/Samples/DivergingBarChart.cs
+++ b/samples/ReactorCharting.Gallery/Samples/DivergingBarChart.cs
@@ -105,7 +105,7 @@ .. items.Select((item, i) =>
                  TextRight(2, top + band.Map(item) + band.Bandwidth / 2 - 7, item, left - 6, 10, ChartMutedForeground)),
 
              // Legend
-             .. D3Legend(left + plotW - 120, top + 2, [("Positive", posBrush), ("Negative", negBrush)]),
+             .. D3Legend(left + plotW - 120, top + 2, ((string, Microsoft.UI.Xaml.Media.SolidColorBrush)[])[("Positive", posBrush), ("Negative", negBrush)]),
 
              D3Charts.Text(left, 4, "Customer Sentiment Scores", 13, ChartForeground),
             ]
diff --git a/samples/ReactorCharting.Gallery/Samples/SlopeChart.cs b/samples/ReactorCharting.Gallery/Samples/SlopeChart.cs
index 696cd9a9e..aab9b50b2 100644
--- a/samples/ReactorCharting.Gallery/Samples/SlopeChart.cs
+++ b/samples/ReactorCharting.Gallery/Samples/SlopeChart.cs
@@ -89,7 +89,7 @@ .. items.SelectMany(item =>
              }),
 
              // Legend
-             .. D3Legend(canvasW / 2 - 80, canvasH - 22, [("Improved", Brush(Palette[2])), ("Declined", Brush(Palette[3]))]),
+             .. D3Legend(canvasW / 2 - 80, canvasH - 22, ((string, Microsoft.UI.Xaml.Media.SolidColorBrush)[])[("Improved", Brush(Palette[2])), ("Declined", Brush(Palette[3]))]),
             ]
         )
             .AutomationName("Department Performance: Before vs After")
diff --git a/samples/TodoApp/Program.cs b/samples/TodoApp/Program.cs
index 95f7d628d..a4bd6eed1 100644
--- a/samples/TodoApp/Program.cs
+++ b/samples/TodoApp/Program.cs
@@ -45,21 +45,21 @@ static class TodoReducer
         AddItem when !string.IsNullOrWhiteSpace(state.NewItemText) =>
             state with
             {
-                Items = [.. state.Items, new(Guid.NewGuid().ToString(), state.NewItemText.Trim(), false)],
+                Items = (TodoItem[])[.. state.Items, new(Guid.NewGuid().ToString(), state.NewItemText.Trim(), false)],
                 NewItemText = ""
             },
         ToggleItem t => state with
         {
-            Items = [.. state.Items.Select(i =>
+            Items = (TodoItem[])[.. state.Items.Select(i =>
                 i.Id == t.Id ? i with { IsCompleted = !i.IsCompleted } : i)]
         },
         DeleteItem d => state with
         {
-            Items = [.. state.Items.Where(i => i.Id != d.Id)]
+            Items = (TodoItem[])[.. state.Items.Where(i => i.Id != d.Id)]
         },
         SetNewItemText s => state with { NewItemText = s.Text },
         SetFilter f => state with { Filter = f.Filter },
-        ClearCompleted => state with { Items = [.. state.Items.Where(i => !i.IsCompleted)] },
+        ClearCompleted => state with { Items = (TodoItem[])[.. state.Items.Where(i => !i.IsCompleted)] },
         _ => state
     };
 }
diff --git a/src/Reactor/Charting/Charts.Tree.cs b/src/Reactor/Charting/Charts.Tree.cs
index 0c6c35aa2..508a27af7 100644
--- a/src/Reactor/Charting/Charts.Tree.cs
+++ b/src/Reactor/Charting/Charts.Tree.cs
@@ -166,7 +166,7 @@ IReadOnlyList<ChartSeriesDescriptor> IChartAccessibilityData.Series
                 return new ChartPointDescriptor(label, node.Depth);
             }).ToArray();
 
-            return [new ChartSeriesDescriptor("Nodes", points)];
+            return (ChartSeriesDescriptor[])[new ChartSeriesDescriptor("Nodes", points)];
         }
     }
 
@@ -390,7 +390,7 @@ IReadOnlyList<ChartSeriesDescriptor> IChartAccessibilityData.Series
                     $"{sourceName} to {targetName}, weight {link.Strength}");
             }).ToArray();
 
-            return [new ChartSeriesDescriptor("Edges", points)];
+            return (ChartSeriesDescriptor[])[new ChartSeriesDescriptor("Edges", points)];
         }
     }
 
diff --git a/src/Reactor/Charting/Charts.cs b/src/Reactor/Charting/Charts.cs
index 43ffc30d9..6d0a8a0ba 100644
--- a/src/Reactor/Charting/Charts.cs
+++ b/src/Reactor/Charting/Charts.cs
@@ -394,7 +394,7 @@ IReadOnlyList<ChartSeriesDescriptor> IChartAccessibilityData.Series
                 return new ChartPointDescriptor(xLabel, yVal, label);
             }).ToArray();
 
-            return [new ChartSeriesDescriptor(seriesName, points)];
+            return (ChartSeriesDescriptor[])[new ChartSeriesDescriptor(seriesName, points)];
         }
     }
 
@@ -407,7 +407,7 @@ IReadOnlyList<ChartAxisDescriptor> IChartAccessibilityData.Axes
             var (xMin, xMax) = D3Extent.Extent(Data, XAccessor);
             var (yMin, yMax) = D3Extent.Extent(Data, YAccessor);
 
-            return [
+            return (ChartAxisDescriptor[])[
                 new ChartAxisDescriptor(ChartAxisType.X, _xAxisLabel, xMin, xMax, _xUnits),
                 new ChartAxisDescriptor(ChartAxisType.Y, _yAxisLabel, yMin, yMax, _yUnits),
             ];
@@ -672,7 +672,7 @@ IReadOnlyList<ChartSeriesDescriptor> IChartAccessibilityData.Series
             }).ToArray();
 
             var seriesName = _seriesNames?.Length > 0 ? _seriesNames[0] : "Slices";
-            return [new ChartSeriesDescriptor(seriesName, points)];
+            return (ChartSeriesDescriptor[])[new ChartSeriesDescriptor(seriesName, points)];
         }
     }
 
diff --git a/src/Reactor/Hosting/ReactorHostControl.cs b/src/Reactor/Hosting/ReactorHostControl.cs
index 44fa1875e..55c3efcb5 100644
--- a/src/Reactor/Hosting/ReactorHostControl.cs
+++ b/src/Reactor/Hosting/ReactorHostControl.cs
@@ -357,7 +357,7 @@ private void Render()
         // additional reset steps, throttling) only need editing here.
         void RecoverFromHookOrder(HookOrderException ex, RenderContext ctx, string mode)
         {
-            _logger.LogWarning(ex,
+            _logger?.LogWarning(ex,
                 "Hot reload: hook order/type changed — resetting {Mode} state and re-rendering",
                 mode);
             ctx.ResetForHotReload();
diff --git a/tests/Reactor.AppTests.Host/Reactor.AppTests.Host.csproj b/tests/Reactor.AppTests.Host/Reactor.AppTests.Host.csproj
index fa1776429..3831405e4 100644
--- a/tests/Reactor.AppTests.Host/Reactor.AppTests.Host.csproj
+++ b/tests/Reactor.AppTests.Host/Reactor.AppTests.Host.csproj
@@ -10,6 +10,14 @@
     <Nullable>enable</Nullable>
     <UseWinUI>true</UseWinUI>
     <WindowsPackageType>None</WindowsPackageType>
+    <!-- CsWinRT1032 (collection-literal targeting non-mutable interface) and
+         CsWinRT1033 (cast through [ComImport] interface) are AOT/trimming
+         warnings about data flowing across a WinRT ABI boundary. The
+         selftest harness uses ITaskbarList3 via classic COM interop and the
+         fixtures pass collection literals into managed Reactor APIs — neither
+         crosses a WinRT projection boundary, and the host is never AOT-
+         published. Suppress to keep selftest code idiomatic. -->
+    <NoWarn>$(NoWarn);CsWinRT1032;CsWinRT1033</NoWarn>
   </PropertyGroup>
 
   <ItemGroup>
diff --git a/tests/Reactor.Tests/Reactor.Tests.csproj b/tests/Reactor.Tests/Reactor.Tests.csproj
index 4389c1266..5b6a88377 100644
--- a/tests/Reactor.Tests/Reactor.Tests.csproj
+++ b/tests/Reactor.Tests/Reactor.Tests.csproj
@@ -11,6 +11,12 @@
     <IsPackable>false</IsPackable>
     <IsTestProject>true</IsTestProject>
     <OutputType>Library</OutputType>
+    <!-- CsWinRT1032 (collection-literal targeting non-mutable interface) and
+         CsWinRT1033 (cast through [ComImport] interface) are AOT/trimming
+         warnings about data flowing across a WinRT ABI boundary. These tests
+         call managed Reactor APIs directly and are never AOT-published, so
+         neither concern applies. Suppress to keep test code idiomatic. -->
+    <NoWarn>$(NoWarn);CsWinRT1032;CsWinRT1033</NoWarn>
   </PropertyGroup>
 
   <ItemGroup>