fix(rendering): normalize empty dispatcher evidence

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

@@ -2569,10 +2569,21 @@ public sealed unsafe partial class WbDrawDispatcher : IDisposable
             Vector3 cameraWorldPosition,
             List<AlphaFingerprint> alphaScratch)
     {
-        int opaqueGroupCount =
+        // The no-VAO production early-out deliberately skips group
-            visibleInstanceCount == 0 ? 0 : opaque.Count;
+        // partitioning, so its reusable opaque/transparent lists may still
-        int transparentGroupCount =
+        // contain the preceding draw's entries. No instances were accepted;
-            visibleInstanceCount == 0 ? 0 : transparent.Count;
+        // those stale scratch entries are not part of this submission and
+        // must not leak into its diagnostic identity.
+        IReadOnlyList<InstanceGroup> acceptedOpaque =
+            visibleInstanceCount == 0
+                ? Array.Empty<InstanceGroup>()
+                : opaque;
+        IReadOnlyList<InstanceGroup> acceptedTransparent =
+            visibleInstanceCount == 0
+                ? Array.Empty<InstanceGroup>()
+                : transparent;
+        int opaqueGroupCount = acceptedOpaque.Count;
+        int transparentGroupCount = acceptedTransparent.Count;
         StableRenderHash128 hash = StableRenderHash128.Create();
         hash.Add(visibleInstanceCount);
         hash.Add(immediateInstanceCount);
@@ -2580,14 +2591,14 @@ public sealed unsafe partial class WbDrawDispatcher : IDisposable
         hash.Add(transparentGroupCount);
         hash.Add(deferTransparent);
         RenderSceneHash128 opaqueDigest =
-            BuildOpaqueSubmissionDigest(opaque);
+            BuildOpaqueSubmissionDigest(acceptedOpaque);
         RenderSceneHash128 transparentDigest =
             BuildTransparentSubmissionDigest(
-                transparent,
+                acceptedTransparent,
                 cameraWorldPosition,
                 alphaScratch);
         RenderSceneHash128 transparentSetDigest =
-            BuildOpaqueSubmissionDigest(transparent);
+            BuildOpaqueSubmissionDigest(acceptedTransparent);
         hash.Add(opaqueDigest.Low);
         hash.Add(opaqueDigest.High);
         hash.Add(transparentDigest.Low);

tests/AcDream.App.Tests/Rendering/Wb/InstanceGroupClearTests.cs

@@ -1,4 +1,5 @@
 using System.Numerics;
+using AcDream.App.Rendering.Scene;
 using AcDream.App.Rendering.Wb;
 using AcDream.Core.Meshing;
 using Xunit;
@@ -138,6 +139,36 @@ public class InstanceGroupClearTests
             reversedSubmission.TransparentSetDigest);
     }
 
+    [Fact]
+    public void DispatcherFingerprint_ZeroVisibleInstancesIgnoresStaleGroupStorage()
+    {
+        WbDrawDispatcher.InstanceGroup stale = MakeCompleteGroup(
+            textureHandle: 0xAA,
+            submissionOrder: 0);
+        var scratch = new List<WbDrawDispatcher.AlphaFingerprint>();
+
+        CurrentRenderDispatcherSubmission expected =
+            WbDrawDispatcher.CreateDispatcherSubmission(
+                visibleInstanceCount: 0,
+                immediateInstanceCount: 0,
+                deferTransparent: false,
+                opaque: [],
+                transparent: [],
+                cameraWorldPosition: Vector3.Zero,
+                alphaScratch: scratch);
+        CurrentRenderDispatcherSubmission actual =
+            WbDrawDispatcher.CreateDispatcherSubmission(
+                visibleInstanceCount: 0,
+                immediateInstanceCount: 0,
+                deferTransparent: false,
+                opaque: [stale],
+                transparent: [stale],
+                cameraWorldPosition: Vector3.Zero,
+                alphaScratch: scratch);
+
+        Assert.Equal(expected, actual);
+    }
+
     [Fact]
     public void CachedGroupHandle_RequiresLiveMatchingRegistration()
     {