wip(assembler): round L7 -- shared column cache across workers: whole view 16-19% faster, world unchanged

SharedColumnCache.h: a world-owned, bounded 4-way second-tier cache of exact column values
(heightfield and floating islands), keyed by recipe/plan identity plus content hash, XY and island
id. Lock-free seqlock reads; set-local spin lock on misses. The FLazy thread-local tier stays
first. 83.6% of repeated column work was cross-worker; formula evaluations -60.9%.
W12 L1 view: Luna 2.165 -> 1.754 s; reviewer interleaved 2.059 -> 1.722 s. 8 m crossing new tiles
82 -> 52 ms. +66 MiB peak RSS. All hashes (whole view, per-LOD, exact queries, islands seed 0)
identical at W1/W8/W12, Clang off and GCC default. MSVC/UBT not compiled here.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CSFYgsdW8ejZSyiMf4qRSX

Standalone/Core/src/WorldAssemblerInternal.h

@@ -5,6 +5,7 @@
 #include "VoxelForgeCore/VoxelForgeCore.h"
 
 #include <algorithm>
+#include <atomic>
 #include <bit>
 #include <charconv>
 #include <chrono>
@@ -121,6 +122,9 @@ WorldAssemblyFeatureColumnRangeV1 BuildWorldAssemblyFeatureColumnRangeV1(
 
 namespace world_assembly_detail
 {
+    using FSharedHeightfieldColumnCache =
+        VoxelForgeCoreShared::TSharedColumnValueCache<HeightfieldPointSample,131072,4>;
+
     // Preserve recipe order without allocating or looking up metadata in the point loop.
     // Garder l'ordre de recette sans allocation ni recherche de metadonnees par point.
     struct FeatureRange
@@ -1375,6 +1379,9 @@ namespace world_assembly_detail
         std::array<std::uint8_t, HeightfieldColumnCacheSetCount>> HeightfieldColumnCacheNextWay;
     inline thread_local HeightfieldColumnCacheStats HeightfieldColumnStats{};
     inline thread_local bool HeightfieldColumnCacheLegacyDirectMapped=false;
+    inline thread_local std::array<std::int64_t,4> HeightfieldColumnCaptureBounds{};
+    inline thread_local bool HeightfieldColumnCaptureBoundsValid=false;
+    inline std::atomic<std::uint64_t> HeightfieldColumnCaptureSequence{0};
 
     inline std::size_t HeightfieldColumnCacheSet(const WorldAssemblyRecipeV1& recipe,
         const WorldAssemblyStratumPlanV1& plan,std::int64_t x,std::int64_t y) noexcept
@@ -1587,22 +1594,46 @@ namespace world_assembly_detail
             replacement=&cache[first+replacementWay];
         }
         auto& entry=*replacement;
-        const auto start=std::chrono::steady_clock::now();
-        HeightfieldPointSample column=EvaluateColumn(recipe,plan,x,y);
-        HeightfieldColumnStats.columnComputeMilliseconds+=std::chrono::duration<double,std::milli>(
-            std::chrono::steady_clock::now()-start).count();
         ++HeightfieldColumnStats.columnMisses;
-        if(HeightfieldColumnStats.captureCoordinates&&HeightfieldColumnStats.coordinateCaptureComplete)
+        const auto compute=[&]()
         {
-            try
+            const std::uint64_t sequence=HeightfieldColumnStats.captureCoordinates
+                ?HeightfieldColumnCaptureSequence.fetch_add(1,std::memory_order_relaxed):0;
+            const auto start=std::chrono::steady_clock::now();
+            HeightfieldPointSample result=EvaluateColumn(recipe,plan,x,y);
+            HeightfieldColumnStats.columnComputeMilliseconds+=std::chrono::duration<double,std::milli>(
+                std::chrono::steady_clock::now()-start).count();
+            ++HeightfieldColumnStats.columnEvaluations;
+            if(HeightfieldColumnStats.captureCoordinates
+                &&HeightfieldColumnStats.coordinateCaptureComplete)
             {
-                HeightfieldColumnStats.evaluatedCoordinates.push_back({x,y});
-            }
-            catch(...)
-            {
-                HeightfieldColumnStats.coordinateCaptureComplete=false;
+                try
+                {
+                    const bool outside=HeightfieldColumnCaptureBoundsValid
+                        &&(x<HeightfieldColumnCaptureBounds[0]||x>HeightfieldColumnCaptureBounds[2]
+                            ||y<HeightfieldColumnCaptureBounds[1]||y>HeightfieldColumnCaptureBounds[3]);
+                    HeightfieldColumnStats.evaluatedCoordinates.push_back({x,y,sequence,outside});
+                }
+                catch(...)
+                {
+                    HeightfieldColumnStats.coordinateCaptureComplete=false;
+                }
             }
+            return result;
+        };
+        HeightfieldPointSample column{};
+        if(auto* shared=FSharedHeightfieldColumnCache::threadActive())
+        {
+            const VoxelForgeCoreShared::FColumnCacheKey key{
+                static_cast<std::uint64_t>(reinterpret_cast<std::uintptr_t>(&recipe)),
+                recipe.contentHash,
+                static_cast<std::uint64_t>(reinterpret_cast<std::uintptr_t>(&plan)),
+                plan.contentHash,x,y};
+            bool computed=false;
+            column=shared->getOrCompute(key,compute,computed);
+            if(!computed)++HeightfieldColumnStats.sharedColumnHits;
         }
+        else column=compute();
         entry={&recipe,&plan,recipe.contentHash,plan.contentHash,x,y,column};
         return column;
     }
@@ -2087,10 +2118,22 @@ void Heightfield2D::resetThreadColumnCacheStats(bool captureCoordinates, bool cl
     Stats.columnHits=0;
     Stats.columnMisses=0;
     Stats.columnConflictMisses=0;
+    Stats.sharedColumnHits=0;
+    Stats.columnEvaluations=0;
     Stats.columnComputeMilliseconds=0.0;
     Stats.captureCoordinates=captureCoordinates;
     Stats.coordinateCaptureComplete=true;
     Stats.evaluatedCoordinates.clear();
+    world_assembly_detail::HeightfieldColumnCaptureBoundsValid=false;
+}
+
+void Heightfield2D::setThreadColumnCaptureBounds(std::int64_t minimumXSubvoxels,
+    std::int64_t minimumYSubvoxels,std::int64_t maximumXSubvoxels,
+    std::int64_t maximumYSubvoxels) noexcept
+{
+    world_assembly_detail::HeightfieldColumnCaptureBounds={minimumXSubvoxels,
+        minimumYSubvoxels,maximumXSubvoxels,maximumYSubvoxels};
+    world_assembly_detail::HeightfieldColumnCaptureBoundsValid=true;
 }
 
 void Heightfield2D::setThreadColumnCacheLegacyDirectMapped(bool enabled) noexcept