phase(N.5) Task 8: InstanceGroup + GroupKey carry bindless handle + layer

Replaces uint TextureHandle (32-bit GL name) with ulong
BindlessTextureHandle (64-bit) in InstanceGroup + GroupKey + ResolveTexture
return type. Adds TextureLayer (always 0 for per-instance composites,
becomes meaningful when WB atlas is adopted in N.6).

ClassifyBatches now calls TextureCache.GetOrUpload*Bindless variants —
these return Texture2DArray-backed bindless handles (Task 3 work).

DrawGroup body throws NotImplementedException — Task 10 rewrites the
whole Draw() method to use glMultiDrawElementsIndirect, which makes
DrawGroup obsolete. CPU-only tests don't invoke DrawGroup so the build
+ test gates stay green; visual launch fails until Task 10 (intentional).

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

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

@@ -398,21 +398,10 @@ public sealed unsafe class WbDrawDispatcher : IDisposable
 
     private void DrawGroup(InstanceGroup grp)
     {
-        _gl.ActiveTexture(TextureUnit.Texture0);
-        _gl.BindTexture(TextureTarget.Texture2D, grp.TextureHandle);
-        _gl.BindBuffer(BufferTargetARB.ElementArrayBuffer, grp.Ibo);
-
-        // BaseInstance offsets the per-instance attribute fetches into our
-        // shared instance VBO so each group reads its own slice. Requires
-        // GL_ARB_base_instance (GL 4.2+); WB requires 4.3 so this is available.
-        _gl.DrawElementsInstancedBaseVertexBaseInstance(
-            PrimitiveType.Triangles,
-            (uint)grp.IndexCount,
-            DrawElementsType.UnsignedShort,
-            (void*)(grp.FirstIndex * sizeof(ushort)),
-            (uint)grp.InstanceCount,
-            grp.BaseVertex,
-            (uint)grp.FirstInstance);
+        throw new NotImplementedException(
+            "DrawGroup is being removed in Task 10 — the dispatcher rewrites Draw() " +
+            "to use glMultiDrawElementsIndirect instead of per-group draws. " +
+            "If this throws at runtime, Task 10 hasn't landed yet.");
     }
 
     private void MaybeFlushDiag()
@@ -452,12 +441,16 @@ public sealed unsafe class WbDrawDispatcher : IDisposable
                     : TranslucencyKind.Opaque;
             }
 
-            uint texHandle = ResolveTexture(entity, meshRef, batch, palHash);
+            ulong texHandle = ResolveTexture(entity, meshRef, batch, palHash);
             if (texHandle == 0) continue;
 
+            // TextureLayer is always 0 for per-instance composites; non-zero when
+            // WB atlas is adopted in N.6+ and batches reference a shared atlas layer.
+            uint texLayer = 0;
+
             var key = new GroupKey(
                 batch.IBO, batch.FirstIndex, (int)batch.BaseVertex,
-                batch.IndexCount, texHandle, translucency);
+                batch.IndexCount, texHandle, texLayer, translucency);
 
             if (!_groups.TryGetValue(key, out var grp))
             {
@@ -467,7 +460,8 @@ public sealed unsafe class WbDrawDispatcher : IDisposable
                     FirstIndex = batch.FirstIndex,
                     BaseVertex = (int)batch.BaseVertex,
                     IndexCount = batch.IndexCount,
-                    TextureHandle = texHandle,
+                    BindlessTextureHandle = texHandle,
+                    TextureLayer = texLayer,
                     Translucency = translucency,
                 };
                 _groups[key] = grp;
@@ -476,10 +470,8 @@ public sealed unsafe class WbDrawDispatcher : IDisposable
         }
     }
 
-    private uint ResolveTexture(WorldEntity entity, MeshRef meshRef, ObjectRenderBatch batch, ulong palHash)
+    private ulong ResolveTexture(WorldEntity entity, MeshRef meshRef, ObjectRenderBatch batch, ulong palHash)
     {
-        // WB stores the surface id on batch.Key.SurfaceId (TextureKey struct);
-        // batch.SurfaceId is unset (zero) for batches built by ObjectMeshManager.
         uint surfaceId = batch.Key.SurfaceId;
         if (surfaceId == 0 || surfaceId == 0xFFFFFFFF) return 0;
 
@@ -490,19 +482,16 @@ public sealed unsafe class WbDrawDispatcher : IDisposable
 
         if (entity.PaletteOverride is not null)
         {
-            // perf #4: pass the entity-precomputed palette hash so TextureCache
-            // can skip its internal HashPaletteOverride for repeat lookups
-            // within the same character.
-            return _textures.GetOrUploadWithPaletteOverride(
+            return _textures.GetOrUploadWithPaletteOverrideBindless(
                 surfaceId, origTexOverride, entity.PaletteOverride, palHash);
         }
         else if (hasOrigTexOverride)
         {
-            return _textures.GetOrUploadWithOrigTextureOverride(surfaceId, overrideOrigTex);
+            return _textures.GetOrUploadWithOrigTextureOverrideBindless(surfaceId, overrideOrigTex);
         }
         else
         {
-            return _textures.GetOrUpload(surfaceId);
+            return _textures.GetOrUploadBindless(surfaceId);
         }
     }
 
@@ -545,7 +534,8 @@ public sealed unsafe class WbDrawDispatcher : IDisposable
         uint FirstIndex,
         int BaseVertex,
         int IndexCount,
-        uint TextureHandle,
+        ulong BindlessTextureHandle,
+        uint TextureLayer,
         TranslucencyKind Translucency);
 
     private sealed class InstanceGroup
@@ -554,7 +544,8 @@ public sealed unsafe class WbDrawDispatcher : IDisposable
         public uint FirstIndex;
         public int BaseVertex;
         public int IndexCount;
-        public uint TextureHandle;
+        public ulong BindlessTextureHandle;   // 64-bit (was uint TextureHandle in N.4)
+        public uint TextureLayer;             // 0 for per-instance composites; non-zero when WB atlas is adopted in N.6+
         public TranslucencyKind Translucency;
         public int FirstInstance;   // offset into the shared instance VBO (in instances, not bytes)
         public int InstanceCount;