standalone: cheap chunk crossings -- exact-tile slab compile, nearest tiles first (~1.2 s -> 121 ms peak)

- Core compiles exact-tile analytic slabs for entering tiles; a Z-column sampler reuses the coherent
  noise context along each tile column; the viewer keeps residents and prioritises nearby tiles.
- 30-crossing straight flight: nearest tile ready 15.8 ms median / 27.6 ms max; full crossing wall
  121 ms peak; worker CPU per crossing 545 ms median, 834 ms max.
- W1/W8 hashes equal; routes 5642/5642; look, passage, stair, thin-sheet, coarse-panel and far
  audits pass; bad-shell control fails; path-hash audit kept.
Cold whole view, measured by me interleaved (busy machine): 1.242 s vs 1.255 s for 3b37d57, parity.
Still open from the owner (LOD0): fins along a strata seam, choppy stair facets.

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

Standalone/Source/VoxelForge/Private/VoxelMarchingCubesMesher.cpp

@@ -1040,9 +1040,49 @@ FVoxelMeshData UVoxelMarchingCubesMesher::GenerateMesh(FIntVector OriginVoxels,
         const int64 TileExtentVoxels = static_cast<int64>(Step) * CellsPerAxis;
         const bool bUseVerticalCacheTraversal = TileExtentVoxels > CHUNK_SIZE * 16;
         const FStandaloneShapeWorld* ActiveShapeWorld=ShapeWorldContext;
+        const bool bUseShapeWorldZBatch=ActiveShapeWorld!=nullptr
+            &&ActiveShapeWorld->IsAnalyticOnly()
+            &&!bUseSharedDensityGrid&&!bCapturePreEditGrid;
         const bool bUseShapeWorldXBatch=ActiveShapeWorld!=nullptr
             &&!bUseSharedDensityGrid&&!bCapturePreEditGrid;
-        if (bUseVerticalCacheTraversal)
+        if(bUseShapeWorldZBatch&&!bUseVerticalCacheTraversal)
+        {
+            for(const std::vector<int32>& YGroup:YGroups)
+            for(const std::vector<int32>& XGroup:XGroups)
+            for(const int32 gy:YGroup)
+            for(const int32 gx:XGroup)
+            {
+                if(ShouldAbortWork())
+                {
+                    if(bUseOperatorBlock){Generator->EndDensityBlock();}
+                    return FVoxelMeshData();
+                }
+                const int32 BatchCount=GzHi-GzLo+1;
+                const int32 SampleX=OriginVoxels.X+gx*Step;
+                const int32 SampleY=OriginVoxels.Y+gy*Step;
+                float Densities[CHUNK_SIZE+3]{};
+                ActiveShapeWorld->DensityAtLatticeZRun(SampleX,SampleY,
+                    OriginVoxels.Z+GzLo*Step,Step,BatchCount,Densities);
+                for(int32 Lane=0;Lane<BatchCount;++Lane)
+                {
+                    const int32 LocalGz=GzLo+Lane;
+                    const int32 LocalIndex=
+                        ((LocalGz+1)*MDim+(gy+1))*MDim+(gx+1);
+                    DensityGrid[LocalIndex]=Densities[Lane];
+                }
+                const int32 ReachBlockX=FMath::Clamp(gx,0,CellsPerAxis-1)
+                    /VoxelGenLOD::TileReachBlockCells;
+                const int32 ReachBlockY=FMath::Clamp(gy,0,CellsPerAxis-1)
+                    /VoxelGenLOD::TileReachBlockCells;
+                const int32 ReachBlockZ=FMath::Clamp(GzHi,0,CellsPerAxis-1)
+                    /VoxelGenLOD::TileReachBlockCells;
+                VoxelGenLOD::TileReachBlockIndex=
+                    ((ReachBlockZ*ReachBlocksPerAxis)+ReachBlockY)
+                        *ReachBlocksPerAxis+ReachBlockX;
+                if(OutDensitySampleCount)*OutDensitySampleCount+=BatchCount;
+            }
+        }
+        else if (bUseVerticalCacheTraversal)
         {
             for (const std::vector<int32>& YGroup : YGroups)
             for (const std::vector<int32>& XGroup : XGroups)