wip(assembler): M1 round 4 -- cap rebuilt (no hiding), sub-voxel audit, routes + mesh-free queries

Luna, M1 round 4 (resumed after the night stop):
- Cliff: sub-voxel audit (29,929 half-voxel XY columns, min run 3.75 voxels, 0 subvoxel runs;
  old taper control exposes 20,963) and a root-line shelf at the two-voxel minimum.
- Horizon slab = aliased LOD8 cap ceiling. The first fix hid the ceiling at LOD8 (challenged:
  enclosed, interior-lit strates); now the LOD8 cap is rebuilt deterministically from the
  native heightfield, skirts preserved; looking up and out shows the cap present.
- Routes: review manifest with 33 stable-ID route points + capsule/support constraints; capsule
  sweep 0 blocked samples / 0 unsupported centres, negative control detected.
- Server path: World::densityAt answers without render meshes. Physics cooking not available
  standalone.
- Hashes (evaluator + 2,226-tile stream) identical at W1/W8/W16. LOD8: 4.446 s for 529 tiles,
  14.25 M field calls, 165 unknown tiles.
- Captures at 60 fps cap + vsync (owner's GPU coil whine). One cliff probe crossed the ~8 GB
  guard (7.69 GiB) and was stopped before capturing.
My review: cap view matches legacy closely, no slab; native cliff is a clean attached ledge
(cleaner than legacy); a few small spikes on the ridge top.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MmSoF64BbRFmk9C3p1VsBJ

Standalone/Core/src/FarShellsInternal.h

@@ -794,7 +794,18 @@ inline void AppendFarConnectorShells(const FStandaloneShapeWorld& Shape,const FV
     for(int32 I=0;I<CeilingStart;++I)CombinedTriangles.Add(Mesh.Triangles[I]);
     for(const int32 Index:NewTriangles)CombinedTriangles.Add(OldSurfaceVertices+Index);
     for(int32 I=CeilingStart;I<Mesh.Triangles.Num();++I)CombinedTriangles.Add(Mesh.Triangles[I]);
+    const int32 OldTriangleCount=Mesh.Triangles.Num()/3;
+    TArray<uint8> ExistingFaceMasks=Mesh.TriangleSkirtFaceMasks;
+    ExistingFaceMasks.SetNum(OldTriangleCount);
+    TArray<uint8> CombinedFaceMasks;CombinedFaceMasks.Reserve(
+        OldTriangleCount+static_cast<int32>(NewTriangles.size()/3));
+    for(int32 Triangle=0;Triangle<CeilingStart/3;++Triangle)
+        CombinedFaceMasks.Add(ExistingFaceMasks[Triangle]);
+    for(size_t Triangle=0;Triangle<NewTriangles.size()/3;++Triangle)CombinedFaceMasks.Add(0);
+    for(int32 Triangle=CeilingStart/3;Triangle<OldTriangleCount;++Triangle)
+        CombinedFaceMasks.Add(ExistingFaceMasks[Triangle]);
     Mesh.Triangles=std::move(CombinedTriangles);
+    Mesh.TriangleSkirtFaceMasks=std::move(CombinedFaceMasks);
     Mesh.NumSurfaceVertices=OldSurfaceVertices+AddedVertices;
 }
 
@@ -1029,5 +1040,17 @@ inline void AppendFarStratumShells(const FStandaloneOwnerWorld& World,const FSta
     for(int32 I=0;I<CeilingStart;++I)CombinedTriangles.Add(Mesh.Triangles[I]);
     for(const int32 Index:NewTriangles)CombinedTriangles.Add(OldSurfaceVertices+Index);
     for(int32 I=CeilingStart;I<Mesh.Triangles.Num();++I)CombinedTriangles.Add(Mesh.Triangles[I]);
-    Mesh.Triangles=std::move(CombinedTriangles);Mesh.NumSurfaceVertices=OldSurfaceVertices+AddedVertices;
+    const int32 OldTriangleCount=Mesh.Triangles.Num()/3;
+    TArray<uint8> ExistingFaceMasks=Mesh.TriangleSkirtFaceMasks;
+    ExistingFaceMasks.SetNum(OldTriangleCount);
+    TArray<uint8> CombinedFaceMasks;CombinedFaceMasks.Reserve(
+        OldTriangleCount+static_cast<int32>(NewTriangles.size()/3));
+    for(int32 Triangle=0;Triangle<CeilingStart/3;++Triangle)
+        CombinedFaceMasks.Add(ExistingFaceMasks[Triangle]);
+    for(size_t Triangle=0;Triangle<NewTriangles.size()/3;++Triangle)CombinedFaceMasks.Add(0);
+    for(int32 Triangle=CeilingStart/3;Triangle<OldTriangleCount;++Triangle)
+        CombinedFaceMasks.Add(ExistingFaceMasks[Triangle]);
+    Mesh.Triangles=std::move(CombinedTriangles);
+    Mesh.TriangleSkirtFaceMasks=std::move(CombinedFaceMasks);
+    Mesh.NumSurfaceVertices=OldSurfaceVertices+AddedVertices;
 }