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/ShapeWorldInternal.h

@@ -1153,6 +1153,33 @@ private:
     }
 
 public:
+    bool GetNativeSurfaceHeightsAt(float X,float Y,int32 ChunkZ,
+                                   float& OutGroundZ,float& OutCeilingZ) const
+    {
+        if(!WorldAssembly||!Owner||!Owner->Manager||!Owner->Generator
+            ||!std::isfinite(X)||!std::isfinite(Y))return false;
+        if(Owner->Manager->GetGeneratorTypeForChunk(FIntVector(0,0,ChunkZ))
+            !=ECaveGeneratorType::SurfaceWorld)return false;
+        const int32 StrateIndex=Owner->Manager->GetStrateIndex(
+            static_cast<float>((static_cast<double>(ChunkZ*CHUNK_SIZE+CHUNK_SIZE/2))*VOXEL_SIZE));
+        const auto* Plan=FindWorldAssemblyStratum(StrateIndex,ChunkZ);
+        if(!Plan)return false;
+        constexpr double Scale=static_cast<double>(VoxelForgeCore::WorldAssemblySubvoxelsPerVoxel);
+        const double MaxVoxel=static_cast<double>(std::numeric_limits<int64>::max())/Scale;
+        if(std::abs(static_cast<double>(X))>MaxVoxel||std::abs(static_cast<double>(Y))>MaxVoxel)
+            return false;
+        const auto ToFixed=[](float Value)
+        {return static_cast<int64>(std::llround(static_cast<double>(Value)
+            *VoxelForgeCore::WorldAssemblySubvoxelsPerVoxel));};
+        const VoxelForgeCore::Heightfield2D Block(WorldAssembly->recipe,*Plan);
+        if(!Block.isValid())return false;
+        const auto Column=Block.point(ToFixed(X),ToFixed(Y),
+            static_cast<int64>(ChunkZ)*CHUNK_SIZE*VoxelForgeCore::WorldAssemblySubvoxelsPerVoxel);
+        OutGroundZ=static_cast<float>(Column.groundHeightSubvoxels/Scale);
+        OutCeilingZ=static_cast<float>(Column.capHeightSubvoxels/Scale);
+        return std::isfinite(OutGroundZ)&&std::isfinite(OutCeilingZ);
+    }
+
     EVoxelTileClass ClassifyBox(const FIntVector& Origin,int32 Step,int32 Cells) const
     { return ClassifyBoxDetailed(Origin,Step,Cells).Verdict; }