wip(assembler): round L12 -- region pages keep LOD1 block proofs: 24 m crossing 5x faster

Analytic region pages now retain the immutable shared manifest, so LOD1 page tiles get the L9
uniform-block proofs (71.7 -> 5.6 ms per tile). Reviewer W12 no-hash: 24 m crossing 0.898 ->
0.166 s; Luna: 1 km 5.89 -> 1.25 s. Spawn unchanged; all L1/FloatingIslands hashes and the 24 m
crossing hash unchanged (W1/W12).
KNOWN BUG (pre-existing, measured here): the same tile key yields different density from the base
shape (manifest field) than from a region page (legacy field), sometimes different mesh too, so
output depends on streaming history. To be fixed in L13.

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

Standalone/Core/src/ShapeWorldInternal.h

@@ -319,6 +319,7 @@ public:
         Owner=&World;WorldAssembly=InWorldAssembly;
         WorkerCount=std::clamp(Workers,1,16);DetailVariant=Variant;
         Scheduler=InScheduler;RoundTunnelsEnabled=bInRoundTunnels;
+        bUseNativeManifestFields=true;
         bAnalyticOnly=false;
         bProfileDetailBand=bInProfileDetailBand;
         for(int32 A=0;A<3;++A)
@@ -470,10 +471,16 @@ public:
     bool BuildAnalyticRegion(FStandaloneOwnerWorld& World,const FIntVector& MinVoxels,
                const FIntVector& MaxVoxels,const FIntVector& ClipMinVoxels,
                const FIntVector& ClipMaxVoxels,EDetailVariant Variant,
-               bool bInRoundTunnels,std::string& Error)
+               bool bInRoundTunnels,
+               const VoxelForgeCore::WorldAssemblyManifest* InWorldAssembly,
+               std::string& Error)
     {
         using Clock=std::chrono::steady_clock;
-        Owner=&World;WorkerCount=1;DetailVariant=Variant;Scheduler=nullptr;
+        Owner=&World;WorldAssembly=InWorldAssembly;
+        WorkerCount=1;DetailVariant=Variant;Scheduler=nullptr;
+        // Region pages use the immutable manifest for conservative block proofs, while keeping
+        // the legacy SurfaceWorld density evaluator so existing tile hashes remain exact.
+        bUseNativeManifestFields=false;
         RoundTunnelsEnabled=bInRoundTunnels;bAnalyticOnly=true;bProfileDetailBand=false;
         for(int32 A=0;A<3;++A)
         {
@@ -509,7 +516,7 @@ public:
     {
         Owner=&World;WorldAssembly=InWorldAssembly;
         NativeOnlyMinimum=InMinimum;NativeOnlyMaximum=InMaximum;
-        bNativeOnly=true;bAnalyticOnly=true;Built=true;
+        bUseNativeManifestFields=true;bNativeOnly=true;bAnalyticOnly=true;Built=true;
         NativeOnlyViolations.store(0,std::memory_order_relaxed);
     }
 
@@ -2050,7 +2057,7 @@ private:
 
     bool NativeSurfaceDensityAt(float X,float Y,float Z,float& OutDensity) const
     {
-        if(!WorldAssembly||!Owner||!Owner->Manager||!Owner->Generator
+        if(!bUseNativeManifestFields||!WorldAssembly||!Owner||!Owner->Manager||!Owner->Generator
             ||!std::isfinite(X)||!std::isfinite(Y)||!std::isfinite(Z))return false;
         const int32 ChunkZ=FMath::FloorToInt(Z/static_cast<float>(CHUNK_SIZE));
         if(Owner->Manager->GetGeneratorTypeForChunk(FIntVector(0,0,ChunkZ))
@@ -2075,7 +2082,7 @@ private:
 
     bool NativeFloatingIslandDensityAt(float X,float Y,float Z,float& OutDensity) const
     {
-        if(!WorldAssembly||!Owner||!Owner->Manager||!Owner->Generator
+        if(!bUseNativeManifestFields||!WorldAssembly||!Owner||!Owner->Manager||!Owner->Generator
             ||!std::isfinite(X)||!std::isfinite(Y)||!std::isfinite(Z))return false;
         // Convert Core query Z back to the owner's legacy chunk coordinate.
         // Convertir Z du Core vers la coordonnee de chunk legacy du proprietaire.
@@ -5360,6 +5367,7 @@ private:
     EDetailVariant DetailVariant=EDetailVariant::Coherent;
     bool Built=false;
     bool bNativeOnly=false;
+    bool bUseNativeManifestFields=false;
     FIntVector NativeOnlyMinimum=FIntVector::ZeroValue;
     FIntVector NativeOnlyMaximum=FIntVector::ZeroValue;
     mutable std::atomic<uint32> NativeOnlyViolations{0};