phase(N.5) Task 11: translucency partition contract test

Locks in Decision 2 (Opaque + ClipMap → opaque indirect; AlphaBlend +
Additive + InvAlpha → transparent indirect). Catches future refactors
that drift the partition — silent visual regression otherwise (groups
rendered in the wrong pass with the wrong blend state).

Adds public static IsOpaquePublic shim on WbDrawDispatcher; the
underlying IsOpaque stays private.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/AcDream.App/Rendering/Wb/WbDrawDispatcher.cs

@@ -643,6 +643,13 @@ public sealed unsafe class WbDrawDispatcher : IDisposable
         return new IndirectLayoutResult(opaqueCount, transparentCount, opaqueCount * DrawCommandStride);
     }
 
+    /// <summary>
+    /// Public test shim for <see cref="IsOpaque"/>. Locks in the N.5 Decision 2
+    /// translucency partition: Opaque + ClipMap → opaque indirect; AlphaBlend +
+    /// Additive + InvAlpha → transparent indirect.
+    /// </summary>
+    public static bool IsOpaquePublic(TranslucencyKind t) => IsOpaque(t);
+
     private static bool IsOpaque(TranslucencyKind t)
         => t == TranslucencyKind.Opaque || t == TranslucencyKind.ClipMap;
 

tests/AcDream.Core.Tests/Rendering/Wb/WbDrawDispatcherTranslucencyTests.cs

@@ -0,0 +1,25 @@
+using AcDream.App.Rendering.Wb;
+using AcDream.Core.Meshing;
+using Xunit;
+
+namespace AcDream.Core.Tests.Rendering.Wb;
+
+/// <summary>
+/// Locks in the N.5 translucency partition contract (spec Decision 2).
+/// If the partition drifts, the dispatcher's opaque + transparent indirect
+/// passes will silently render the wrong groups in the wrong pass — visible
+/// regression that's hard to spot in code review.
+/// </summary>
+public sealed class WbDrawDispatcherTranslucencyTests
+{
+    [Theory]
+    [InlineData(TranslucencyKind.Opaque,     true)]
+    [InlineData(TranslucencyKind.ClipMap,    true)]
+    [InlineData(TranslucencyKind.AlphaBlend, false)]
+    [InlineData(TranslucencyKind.Additive,   false)]
+    [InlineData(TranslucencyKind.InvAlpha,   false)]
+    public void IsOpaque_PartitionsByKind(TranslucencyKind kind, bool expected)
+    {
+        Assert.Equal(expected, WbDrawDispatcher.IsOpaquePublic(kind));
+    }
+}