wip(assembler): round S10 -- LOD8 horizon sampled at MC spacing: LOD8 worker time 18.8 s -> 4.3 s

Planar far horizon samples the LOD8 interior at the MC cell spacing, keeping
128-voxel boundary strips; far recipe v3. LOD8 p95 59.8 -> 13.9 ms, spawn
worker-seconds ~41 -> 26.9, full set 7.8 -> 7.1 s, ring 0.49 s, LOD0 1.43 s,
40 m/s ring 75/75. S3/S4 2 cm agreement, 100% cap coverage, W1/W8/W12 and
W1/W8/W16 determinism pass. Report: Standalone/Research/WorldAssemblerM3/Round14.

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

Standalone/Source/StreamingWorld.h

@@ -423,11 +423,15 @@ public:
                                            bool bInSkipMaterialGroups=false,
                                            bool bInSkipUV=false,
                                            bool bInSkipColors=false,
-                                           VoxelForgeCore::World* InCoreWorld=nullptr)
+                                           VoxelForgeCore::World* InCoreWorld=nullptr,
+                                           bool bInCaptureFarColumnCoordinates=false,
+                                           int32 InLod8HorizonInteriorStepVoxels=0)
         :World(&InWorld),WorkerCount(FMath::Clamp(InWorkerCount,1,16)),bHashDensity(bInHashDensity),
          MeshCache(InMeshCache),MaxLevelFilter(InMaxLevelFilter),
          CoreWorld(InCoreWorld),bSkipUvAndColors(bInSkipUvAndColors),bSkipMaterialGroups(bInSkipMaterialGroups),
-         bSkipUV(bInSkipUV),bSkipColors(bInSkipColors)
+         bSkipUV(bInSkipUV),bSkipColors(bInSkipColors),
+         bCaptureFarColumnCoordinates(bInCaptureFarColumnCoordinates),
+         Lod8HorizonInteriorStepVoxels(std::max(0,InLod8HorizonInteriorStepVoxels))
     {
         VoxelGenLOD::InitializeConsoleSwitches();
         UVoxelMarchingCubesMesher::InitializeConsoleSwitches();
@@ -795,6 +799,8 @@ private:
             Options.bandMinZVoxel=Job.BandZMin;Options.bandMaxZVoxel=Job.BandZMax;
             Options.hashDensity=bHashDensity;Options.skipUvAndColors=bSkipUvAndColors;
             Options.skipMaterialGroups=bSkipMaterialGroups;Options.skipUv=bSkipUV;Options.skipColors=bSkipColors;
+            Options.captureColumnCoordinates=bCaptureFarColumnCoordinates&&Level==8;
+            Options.lod8HorizonInteriorStepVoxels=Lod8HorizonInteriorStepVoxels;
             std::string Error;
             auto Result=CoreWorld->generateTile(
                 {{Job.Key.Coord.X,Job.Key.Coord.Y,Job.Key.Coord.Z},Job.Key.Level},Options,Error);
@@ -965,6 +971,8 @@ private:
     bool bSkipMaterialGroups=false;
     bool bSkipUV=false;
     bool bSkipColors=false;
+    bool bCaptureFarColumnCoordinates=false;
+    int32 Lod8HorizonInteriorStepVoxels=0;
     std::atomic<uint64> CacheHitCount{0};
     mutable std::mutex Mutex;
     std::condition_variable Wake;