perf(core): FI LOD0 attribution, exact Z-inner traversal; fix a mesh gap at the passage shaft foot (L57); R26

Sampled cycle attribution of FI LOD0 field work: grid fill 83%, boundary 13%, skirts 4%; island roots,
columns and helix dominate, the column cache path is real but secondary (no thrashing). FI-only Z-inner
traversal at LOD0 (same lattice samples, exact) cuts FI whole view 5.35 -> 5.03 s and moving p50 by 12%;
global Z-inner and <=4-island culling were measured and rejected. The meshing band now includes the planned
passage support column's conservative bounds, closing a real gap where the arrival shaft meets the floor
(WorldAssemblyEvaluatorVersion 208 -> 209). fast/medium/full PASS, Clang and GCC.
Research R26 (self-checked): native lattice (maze/shaft) generator design.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016dhxM43dnWvUu2B5Ph1iG1

Standalone/Core/src/ShapeWorldInternal.h

@@ -8,6 +8,7 @@
 #include "VoxelDensityPrimitives.h"
 #include "VoxelForgeCore/VoxelForgeCore.h"
 #include "VoxelForgeFieldShared.h"
+#include "VoxelForgeCore/FloatingIslandInstrumentation.h"
 
 #include <algorithm>
 #include <array>
@@ -414,6 +415,12 @@ public:
         return FindBoundStratumForChunk(FMath::FloorToInt(Z/LayoutWidth));
     }
 
+    bool IsFloatingIslandFieldAtZ(float Z) const
+    {
+        const FBoundStratumField* Bound=FindBoundStratumForZ(Z);
+        return Bound&&Bound->Kind==FBoundStratumField::EKind::FloatingIslands;
+    }
+
     const FBoundStratumField* FindBoundStratumForManagerZ(float Z) const
     {
         if(!std::isfinite(Z)||!Owner||!(BoundManagerLayoutChunkWidthVoxels>0.0f))
@@ -6139,6 +6146,7 @@ private:
         const auto* FieldAdapter=std::get_if<FFloatingIslandFieldAdapter>(
             &Bound->Evaluator);
         if(!FieldAdapter||!FieldAdapter->Evaluator.isValid())return false;
+        VoxelForgeCore::floating_island_detail::FScopedIslandAttributionSample attributionSample;
         constexpr double Scale=static_cast<double>(VoxelForgeCore::WorldAssemblySubvoxelsPerVoxel);
         constexpr double Maximum=1000000000000.0/Scale;
         if(std::abs(static_cast<double>(X))>Maximum||std::abs(static_cast<double>(Y))>Maximum
@@ -6266,8 +6274,12 @@ private:
         }
         if(mouthFilterWeight>0.0)
         {
+            VoxelForgeCore::floating_island_detail::FScopedIslandAttributionTimer mouthFilterTimer(
+                VoxelForgeCore::floating_island_detail::EIslandAttributionBucket::MouthFilter);
             constexpr std::int64_t FilterStep=8*VoxelForgeCore::WorldAssemblySubvoxelsPerVoxel;
             std::int64_t weightedSum=0;
+            VoxelForgeCore::floating_island_detail::FScopedIslandFieldCaller passageFilterCaller(
+                VoxelForgeCore::floating_island_detail::EIslandFieldCaller::PassageFilter);
             for(int dz=-1;dz<=1;++dz)
                 for(int dy=-1;dy<=1;++dy)
                     for(int dx=-1;dx<=1;++dx)
@@ -6306,6 +6318,8 @@ private:
             {
                 bool surroundedByAir=true;
                 std::int64_t minimumAirDensity=std::numeric_limits<std::int64_t>::max();
+                VoxelForgeCore::floating_island_detail::FScopedIslandFieldCaller passageFilterCaller(
+                    VoxelForgeCore::floating_island_detail::EIslandFieldCaller::PassageFilter);
                 for(std::size_t axis=0;axis<3&&surroundedByAir;++axis)
                     for(const int sign:{-1,1})
                     {
@@ -6323,6 +6337,8 @@ private:
                 if(surroundedByAir)Density=std::max(Density,minimumAirDensity);
             }
         }
+        VoxelForgeCore::floating_island_detail::FScopedIslandAttributionTimer boundaryTimer(
+            VoxelForgeCore::floating_island_detail::EIslandAttributionBucket::Boundary);
         const std::int64_t Bottom=Plan->manifest.recipe.layoutMinimumZSubvoxels;
         const std::int64_t Top=Plan->manifest.recipe.layoutMaximumZSubvoxels;
         const std::int64_t Seal=Plan->manifest.recipe.boundarySealSubvoxels;