standalone: owner review fixes -- paged streaming in Core, no LOD fins, LOD0 stair patches fixed

From the owner's fly-through ("very impressive, in some cases slightly better than the original"):
- Streaming: Core compiles world-aligned fine-detail pages for tiles entering the view and releases
  them when they leave; the viewer keeps resident tiles. One chunk crossing: 144 new tiles, 1,822
  kept (was a full rebuild). A tile built as a late page hashes identically (density, mesh, payload,
  topology) to the same tile from an initial build.
- LOD>=1 fins: off-surface planar connector panels are now checked against the source surface and
  projected onto it; coarse audit 0 off-surface panels; far survival passes, bad-shell still fails.
- LOD0 stair patches: 2,630 sign-changing edges had one endpoint at the fixed +-4.125 fallback
  (carve surfaces were excluded from distance storage); distances now completed analytically, 462
  packed signs corrected; the audit now fails on any sign edge missing either endpoint (0 of 952,997).
- W1/W8 hashes equal; routes 5642/5642; look, passage and far audits pass.
Verified by me, interleaved (8 workers, cold): 1.014 s vs 1.008 s for aeeedaa, no regression.
Open: a chunk crossing still costs ~1.2 s of page compilation.

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

Standalone/Core/src/FarShellsInternal.h

@@ -255,6 +255,7 @@ inline void AppendFarConnectorShells(const FStandaloneShapeWorld& Shape,const FV
     std::vector<FVector2f> NewUVs;
     std::vector<FColor> NewColors;
     std::vector<int32> NewTriangles;
+    std::vector<std::array<int32,4>> NewQuads;
     const int32 OldVertexCount=Mesh.Vertices.Num();
     const int32 OldSurfaceVertices=std::clamp(Mesh.NumSurfaceVertices,0,OldVertexCount);
     const bool bHasUVs=Mesh.UVs.Num()==OldVertexCount;
@@ -579,7 +580,7 @@ inline void AppendFarConnectorShells(const FStandaloneShapeWorld& Shape,const FV
                             const int32 C=RingVertexIndex[Ring+1][FaceSide];
                             const int32 D=RingVertexIndex[Ring+1][Next];
                             // Shared panels are emitted once even when both adjoining radial rays are missing.
-                            NewTriangles.insert(NewTriangles.end(),{A,C,B,B,C,D});
+                            NewQuads.push_back({A,B,C,D});
                         }
                     }
                 }
@@ -587,7 +588,191 @@ inline void AppendFarConnectorShells(const FStandaloneShapeWorld& Shape,const FV
             RunStart=RunEnd+1;
         }
     }
-    if(NewVertices.empty()||NewTriangles.empty())return;
+    if(NewVertices.empty()||NewQuads.empty())return;
+
+    // The survival repair normally emits long connected strips. A few isolated
+    // two-triangle panels can be assembled from a radius borrowed at another axial
+    // sample, though, leaving a free-edged fin away from the sampled density surface.
+    // Match the visible coarse-panel audit's topology and six density samples here.
+    std::vector<uint8> QuadUseCount(NewVertices.size(),0);
+    for(const auto& Quad:NewQuads)
+        for(const int32 Vertex:Quad)
+            if(Vertex>=0&&static_cast<size_t>(Vertex)<QuadUseCount.size()
+                &&QuadUseCount[static_cast<size_t>(Vertex)]<255)
+                ++QuadUseCount[static_cast<size_t>(Vertex)];
+    std::vector<uint8> KeepQuad(NewQuads.size(),1);
+    std::vector<std::array<int32,4>> RefinedQuads;
+    const double ResidualLimit=std::max(2.0,Step*0.10);
+    const double TileMin[3]={static_cast<double>(TileOrigin.X),static_cast<double>(TileOrigin.Y),
+        static_cast<double>(TileOrigin.Z)};
+    const double TileMax[3]={TileMin[0]+TileExtent,TileMin[1]+TileExtent,TileMin[2]+TileExtent};
+    const auto ToVoxels=[&](int32 Vertex)
+    {
+        return FVector(NewVertices[Vertex].X*0.04,NewVertices[Vertex].Y*0.04,
+            NewVertices[Vertex].Z*0.04);
+    };
+    const auto IsTileBoundaryEdge=[&](const FVector& A,const FVector& B)
+    {
+        for(int32 AxisIndex=0;AxisIndex<3;++AxisIndex)
+        {
+            const double PA=AxisIndex==0?A.X:(AxisIndex==1?A.Y:A.Z);
+            const double PB=AxisIndex==0?B.X:(AxisIndex==1?B.Y:B.Z);
+            if((std::abs(PA-TileMin[AxisIndex])<0.75&&std::abs(PB-TileMin[AxisIndex])<0.75)
+                ||(std::abs(PA-TileMax[AxisIndex])<0.75&&std::abs(PB-TileMax[AxisIndex])<0.75))
+                return true;
+        }
+        return false;
+    };
+    for(size_t QuadIndex=0;QuadIndex<NewQuads.size();++QuadIndex)
+    {
+        const auto& Quad=NewQuads[QuadIndex];
+        if(std::any_of(Quad.begin(),Quad.end(),[&](int32 Vertex)
+            {return Vertex<0||static_cast<size_t>(Vertex)>=QuadUseCount.size()
+                ||QuadUseCount[static_cast<size_t>(Vertex)]!=1;}))continue;
+        const FVector A=ToVoxels(Quad[0]),B=ToVoxels(Quad[1]);
+        const FVector C=ToVoxels(Quad[2]),D=ToVoxels(Quad[3]);
+        const FVector N0=FVector::CrossProduct(C-A,B-A);
+        const FVector N1=FVector::CrossProduct(C-B,D-B);
+        const double Area0=N0.Size(),Area1=N1.Size();
+        const double AreaSum=Area0+Area1;
+        if(AreaSum<=1.0e-12)continue;
+        const double Coherence=(N0+N1).Size()/AreaSum;
+        if(Coherence<0.995)continue;
+        if(IsTileBoundaryEdge(A,B)&&IsTileBoundaryEdge(B,D)
+            &&IsTileBoundaryEdge(D,C)&&IsTileBoundaryEdge(C,A))continue;
+        const FVector Samples[6]={A,B,C,D,(A+C+B)/3.0,(B+C+D)/3.0};
+        int32 OffSourceSamples=0;
+        for(const FVector& P:Samples)
+            if(std::abs(Shape.DensityAt(static_cast<float>(P.X),static_cast<float>(P.Y),
+                static_cast<float>(P.Z)))>ResidualLimit)++OffSourceSamples;
+        if(OffSourceSamples*4<6)continue;
+
+        constexpr int32 Subdivisions=8;
+        const FVector PreferredNormal=(NewNormals[Quad[0]]+NewNormals[Quad[1]]
+            +NewNormals[Quad[2]]+NewNormals[Quad[3]]).GetSafeNormal();
+        const auto SourceGradient=[&](const FVector& P)
+        {
+            constexpr float H=2.0f;
+            const float GX=(Shape.DensityAt(static_cast<float>(P.X+H),static_cast<float>(P.Y),
+                static_cast<float>(P.Z))-Shape.DensityAt(static_cast<float>(P.X-H),
+                static_cast<float>(P.Y),static_cast<float>(P.Z)))*0.25f;
+            const float GY=(Shape.DensityAt(static_cast<float>(P.X),static_cast<float>(P.Y+H),
+                static_cast<float>(P.Z))-Shape.DensityAt(static_cast<float>(P.X),
+                static_cast<float>(P.Y-H),static_cast<float>(P.Z)))*0.25f;
+            const float GZ=(Shape.DensityAt(static_cast<float>(P.X),static_cast<float>(P.Y),
+                static_cast<float>(P.Z+H))-Shape.DensityAt(static_cast<float>(P.X),
+                static_cast<float>(P.Y),static_cast<float>(P.Z-H)))*0.25f;
+            return FVector(GX,GY,GZ);
+        };
+        std::vector<FVector> PatchVertices;
+        std::vector<FVector> PatchNormals;
+        std::vector<FVector2f> PatchUVs;
+        std::vector<FColor> PatchColors;
+        const auto ProjectToSurface=[&](FVector& P,FVector& Normal)
+        {
+            for(int32 Iteration=0;Iteration<12;++Iteration)
+            {
+                const double Density=Shape.DensityAt(static_cast<float>(P.X),
+                    static_cast<float>(P.Y),static_cast<float>(P.Z));
+                if(std::abs(Density)<=0.25)break;
+                FVector Gradient=SourceGradient(P);
+                const double GradientSquared=Gradient.SizeSquared();
+                if(GradientSquared<1.0e-8)return false;
+                double Distance=std::clamp(Density/GradientSquared,-64.0,64.0);
+                P-=Gradient*Distance;
+            }
+            if(std::abs(Shape.DensityAt(static_cast<float>(P.X),static_cast<float>(P.Y),
+                static_cast<float>(P.Z)))>2.0)return false;
+            Normal=SourceGradient(P);
+            if(Normal.SizeSquared()<1.0e-8)return false;
+            Normal.Normalize();
+            if(PreferredNormal.SizeSquared()>1.0e-8&&FVector::DotProduct(Normal,PreferredNormal)<0.0)
+                Normal*= -1.0;
+            return true;
+        };
+        std::vector<int32> Grid(static_cast<size_t>(Subdivisions+1)*(Subdivisions+1),INDEX_NONE);
+        bool bProjectionSucceeded=true;
+        for(int32 Y=0;Y<=Subdivisions&&bProjectionSucceeded;++Y)
+        {
+            const double V=static_cast<double>(Y)/Subdivisions;
+            for(int32 X=0;X<=Subdivisions;++X)
+            {
+                const double U=static_cast<double>(X)/Subdivisions;
+                FVector P=A*((1.0-U)*(1.0-V))+B*(U*(1.0-V))+C*((1.0-U)*V)+D*(U*V);
+                FVector Normal;
+                if(!ProjectToSurface(P,Normal)){bProjectionSucceeded=false;break;}
+                const int32 LocalIndex=static_cast<int32>(PatchVertices.size());
+                Grid[static_cast<size_t>(Y)*(Subdivisions+1)+X]=LocalIndex;
+                PatchVertices.emplace_back(P.X*25.0,P.Y*25.0,P.Z*25.0);
+                PatchNormals.push_back(Normal);
+                if(bHasUVs)
+                {
+                    const FVector2f UA=NewUVs[Quad[0]],UB=NewUVs[Quad[1]];
+                    const FVector2f UC=NewUVs[Quad[2]],UD=NewUVs[Quad[3]];
+                    PatchUVs.emplace_back(static_cast<float>(UA.X*((1-U)*(1-V))+UB.X*(U*(1-V))
+                        +UC.X*((1-U)*V)+UD.X*(U*V)),
+                        static_cast<float>(UA.Y*((1-U)*(1-V))+UB.Y*(U*(1-V))
+                        +UC.Y*((1-U)*V)+UD.Y*(U*V)));
+                }
+                if(bHasColors)PatchColors.push_back(NewColors[Quad[0]]);
+            }
+        }
+        if(!bProjectionSucceeded)continue;
+
+        KeepQuad[QuadIndex]=0;
+        const int32 PatchBase=static_cast<int32>(NewVertices.size());
+        NewVertices.insert(NewVertices.end(),PatchVertices.begin(),PatchVertices.end());
+        NewNormals.insert(NewNormals.end(),PatchNormals.begin(),PatchNormals.end());
+        if(bHasUVs)NewUVs.insert(NewUVs.end(),PatchUVs.begin(),PatchUVs.end());
+        if(bHasColors)NewColors.insert(NewColors.end(),PatchColors.begin(),PatchColors.end());
+        for(int32 Y=0;Y<Subdivisions;++Y)
+            for(int32 X=0;X<Subdivisions;++X)
+            {
+                const int32 A0=PatchBase+Grid[static_cast<size_t>(Y)*(Subdivisions+1)+X];
+                const int32 B0=PatchBase+Grid[static_cast<size_t>(Y)*(Subdivisions+1)+X+1];
+                const int32 C0=PatchBase+Grid[static_cast<size_t>(Y+1)*(Subdivisions+1)+X];
+                const int32 D0=PatchBase+Grid[static_cast<size_t>(Y+1)*(Subdivisions+1)+X+1];
+                RefinedQuads.push_back({A0,B0,C0,D0});
+            }
+    }
+
+    std::vector<std::array<int32,4>> FinalQuads;
+    const size_t KeptQuadCount=static_cast<size_t>(std::count(KeepQuad.begin(),KeepQuad.end(),uint8{1}));
+    FinalQuads.reserve(KeptQuadCount+RefinedQuads.size());
+    for(size_t QuadIndex=0;QuadIndex<NewQuads.size();++QuadIndex)
+        if(KeepQuad[QuadIndex])FinalQuads.push_back(NewQuads[QuadIndex]);
+    FinalQuads.insert(FinalQuads.end(),RefinedQuads.begin(),RefinedQuads.end());
+    if(FinalQuads.empty())return;
+    std::vector<int32> Remap(NewVertices.size(),INDEX_NONE);
+    std::vector<FVector> KeptVertices,KeptNormals;
+    std::vector<FVector2f> KeptUVs;
+    std::vector<FColor> KeptColors;
+    KeptVertices.reserve(FinalQuads.size()*2);KeptNormals.reserve(FinalQuads.size()*2);
+    if(bHasUVs)KeptUVs.reserve(FinalQuads.size()*2);
+    if(bHasColors)KeptColors.reserve(FinalQuads.size()*2);
+    const auto RemapVertex=[&](int32 Vertex)
+    {
+        int32& Mapped=Remap[static_cast<size_t>(Vertex)];
+        if(Mapped==INDEX_NONE)
+        {
+            Mapped=static_cast<int32>(KeptVertices.size());
+            KeptVertices.push_back(NewVertices[static_cast<size_t>(Vertex)]);
+            KeptNormals.push_back(NewNormals[static_cast<size_t>(Vertex)]);
+            if(bHasUVs)KeptUVs.push_back(NewUVs[static_cast<size_t>(Vertex)]);
+            if(bHasColors)KeptColors.push_back(NewColors[static_cast<size_t>(Vertex)]);
+        }
+        return Mapped;
+    };
+    NewTriangles.reserve(KeptQuadCount*6);
+    for(const auto& Quad:FinalQuads)
+    {
+        const int32 A=RemapVertex(Quad[0]),B=RemapVertex(Quad[1]);
+        const int32 C=RemapVertex(Quad[2]),D=RemapVertex(Quad[3]);
+        NewTriangles.insert(NewTriangles.end(),{A,C,B,B,C,D});
+    }
+    NewVertices=std::move(KeptVertices);NewNormals=std::move(KeptNormals);
+    if(bHasUVs)NewUVs=std::move(KeptUVs);
+    if(bHasColors)NewColors=std::move(KeptColors);
 
     const int32 AddedVertices=static_cast<int32>(NewVertices.size());
     auto InsertVertices=[&](auto& Existing,const auto& Added)

Standalone/Core/src/ShapeWorldInternal.h

@@ -319,6 +319,7 @@ public:
 
         Stage=Clock::now();
         ApplyDetailBand(Stats.DetailBandLines);
+        Stats.SurfaceProxyNodes+=CompleteSignEdgeDistances();
         Stats.SurfaceSeconds=std::chrono::duration<double>(Clock::now()-Stage).count();
         ValidatePassageRoutes();
         Built=true;
@@ -782,6 +783,89 @@ public:
         return bPassageOnly?bPassageDetail:(Tested>0&&FlatShare<20.0&&bPass&&bPassageDetail);
     }
 
+    bool AuditGridStairIntegrity() const
+    {
+        uint64 CheckedEdges=0,MissingAny=0,MissingBoth=0;
+        std::array<std::array<int32,4>,8> Examples{};
+        size_t ExampleCount=0;
+        const auto Record=[&](uint64 EdgeMask,uint64 CandidateA,uint64 CandidateB,
+                              int32 X,int32 Y,int32 Z,int32 Axis)
+        {
+            CheckedEdges+=std::popcount(EdgeMask);
+            const uint64 Missing=EdgeMask&~(CandidateA&CandidateB);
+            uint64 AnyMissing=Missing;
+            MissingAny+=std::popcount(Missing);
+            MissingBoth+=std::popcount(EdgeMask&~(CandidateA|CandidateB));
+            while(AnyMissing&&ExampleCount<Examples.size())
+            {
+                const uint32 Bit=std::countr_zero(AnyMissing);AnyMissing&=AnyMissing-1;
+                Examples[ExampleCount++]={X,Y,Z+static_cast<int32>(Bit),Axis};
+            }
+        };
+
+        const size_t Columns=static_cast<size_t>(Size[0])*Size[1];
+        for(size_t Line=0;Line<Columns;++Line)
+        {
+            const int32 X=Min[0]+static_cast<int32>(Line%Size[0]);
+            const int32 Y=Min[1]+static_cast<int32>(Line/Size[0]);
+            const size_t Base=Line*WordsPerZ;
+            for(size_t W=0;W<WordsPerZ;++W)
+            {
+                const size_t Word=Base+W;
+                const uint64 Rock=RockWords[Word],Candidates=CandidateWords[Word];
+                const uint64 PreviousRock=W?RockWords[Word-1]>>63:0;
+                const uint64 PreviousCandidates=W?CandidateWords[Word-1]>>63:0;
+                uint64 Valid=(Size[2]-W*64)>=64?~uint64{0}
+                    :((uint64{1}<<(Size[2]-W*64))-1);
+                if(W==0)Valid&=~uint64{1};
+                const uint64 ShiftedRock=(Rock<<1)|PreviousRock;
+                const uint64 ShiftedCandidates=(Candidates<<1)|PreviousCandidates;
+                Record((Rock^ShiftedRock)&Valid,Candidates,ShiftedCandidates,
+                    X,Y,Min[2]+static_cast<int32>(W*64),2);
+
+                if(X+1<Max[0]+1)
+                {
+                    const size_t Other=Word+WordsPerZ;
+                    Record(Rock^RockWords[Other],Candidates,CandidateWords[Other],
+                        X,Y,Min[2]+static_cast<int32>(W*64),0);
+                }
+                if(Y+1<Max[1]+1)
+                {
+                    const size_t Other=Word+static_cast<size_t>(Size[0])*WordsPerZ;
+                    Record(Rock^RockWords[Other],Candidates,CandidateWords[Other],
+                        X,Y,Min[2]+static_cast<int32>(W*64),1);
+                }
+            }
+        }
+        std::printf("[GridStairDistanceAudit] region=(%d,%d,%d)..(%d,%d,%d) sign_edges=%llu candidate_fallback_edges=%llu both_fallback_edges=%llu status=%s\n",
+            Min[0],Min[1],Min[2],Max[0],Max[1],Max[2],
+            static_cast<unsigned long long>(CheckedEdges),
+            static_cast<unsigned long long>(MissingAny),
+            static_cast<unsigned long long>(MissingBoth),MissingAny==0?"PASS":"FAIL");
+        const auto CandidateAt=[&](int32 X,int32 Y,int32 Z)
+        {
+            if(!Contains(X,Y,Z))return false;
+            const size_t Column=static_cast<size_t>(Y-Min[1])*Size[0]+static_cast<size_t>(X-Min[0]);
+            const size_t Zi=static_cast<size_t>(Z-Min[2]);
+            return (CandidateWords[Column*WordsPerZ+(Zi>>6)]&(uint64{1}<<(Zi&63u)))!=0;
+        };
+        for(size_t I=0;I<ExampleCount;++I)
+        {
+            int32 AX=Examples[I][0],AY=Examples[I][1],AZ=Examples[I][2];
+            int32 BX=AX,BY=AY,BZ=AZ;
+            if(Examples[I][3]==0)++BX;else if(Examples[I][3]==1)++BY;else --BZ;
+            const float AD=DensityAtLattice(AX,AY,AZ),BD=DensityAtLattice(BX,BY,BZ);
+            const float AExact=AnalyticDensityAt(static_cast<float>(AX),static_cast<float>(AY),static_cast<float>(AZ));
+            const float BExact=AnalyticDensityAt(static_cast<float>(BX),static_cast<float>(BY),static_cast<float>(BZ));
+            std::printf("[GridStairDistanceCandidate] a=(%d,%d,%d) b=(%d,%d,%d) axis=%d candidate=(%d,%d) solid=(%d,%d) density=(%.4f,%.4f) exact=(%.4f,%.4f) critical_air=(%d,%d)\n",
+                AX,AY,AZ,BX,BY,BZ,Examples[I][3],CandidateAt(AX,AY,AZ),CandidateAt(BX,BY,BZ),
+                IsRock(AX,AY,AZ),IsRock(BX,BY,BZ),
+                AD,BD,AExact,BExact,
+                IsInsideCriticalAir(AX,AY,AZ),IsInsideCriticalAir(BX,BY,BZ));
+        }
+        return MissingAny==0;
+    }
+
     bool AuditViewSurface(double CameraX,double CameraY,double CameraZ,
                           float Yaw,float Pitch) const
     {
@@ -2812,6 +2896,107 @@ private:
         }
     }
 
+    uint64 CompleteSignEdgeDistances()
+    {
+        uint64 AddedTotal=0,SignCorrections=0;
+        const size_t Columns=static_cast<size_t>(Size[0])*Size[1];
+        for(int32 Pass=0;Pass<4;++Pass)
+        {
+            uint64 AddedThisPass=0;
+            bool bSignChanged=false;
+            const auto EnsureDistance=[&](int32 X,int32 Y,int32 Z)
+            {
+                const size_t Column=static_cast<size_t>(Y-Min[1])*Size[0]
+                    +static_cast<size_t>(X-Min[0]);
+                const size_t Zi=static_cast<size_t>(Z-Min[2]);
+                const size_t Word=Column*WordsPerZ+(Zi>>6);
+                const uint64 Mask=uint64{1}<<(Zi&63u);
+                if(CandidateWords[Word]&Mask)return;
+
+                const float Density=AnalyticDensityAt(static_cast<float>(X),
+                    static_cast<float>(Y),static_cast<float>(Z));
+                const size_t Node=(Zi*static_cast<size_t>(Size[1])
+                    +static_cast<size_t>(Y-Min[1]))*Size[0]
+                    +static_cast<size_t>(X-Min[0]);
+                StoreSurfaceDistance(Node,Density);
+                CandidateWords[Word]|=Mask;
+                ++AddedThisPass;
+
+                const bool bExactRock=Density<0.0f;
+                const bool bPackedRock=(RockWords[Word]&Mask)!=0;
+                if(bExactRock!=bPackedRock)
+                {
+                    if(bExactRock)RockWords[Word]|=Mask;
+                    else RockWords[Word]&=~Mask;
+                    ++SignCorrections;
+                    bSignChanged=true;
+                }
+            };
+
+            for(size_t Line=0;Line<Columns;++Line)
+            {
+                const int32 X=Min[0]+static_cast<int32>(Line%Size[0]);
+                const int32 Y=Min[1]+static_cast<int32>(Line/Size[0]);
+                const size_t Base=Line*WordsPerZ;
+                for(size_t W=0;W<WordsPerZ;++W)
+                {
+                    const size_t Word=Base+W;
+                    const uint64 Rock=RockWords[Word],Candidates=CandidateWords[Word];
+                    const uint64 PreviousRock=W?RockWords[Word-1]>>63:0;
+                    const uint64 PreviousCandidates=W?CandidateWords[Word-1]>>63:0;
+                    uint64 Valid=(Size[2]-W*64)>=64?~uint64{0}
+                        :((uint64{1}<<(Size[2]-W*64))-1);
+                    if(W==0)Valid&=~uint64{1};
+
+                    const uint64 ShiftedRock=(Rock<<1)|PreviousRock;
+                    const uint64 ShiftedCandidates=(Candidates<<1)|PreviousCandidates;
+                    uint64 Missing=((Rock^ShiftedRock)&Valid)
+                        &~(Candidates&ShiftedCandidates);
+                    while(Missing)
+                    {
+                        const uint32 Bit=std::countr_zero(Missing);Missing&=Missing-1;
+                        const int32 Z=Min[2]+static_cast<int32>(W*64+Bit);
+                        EnsureDistance(X,Y,Z);
+                        EnsureDistance(X,Y,Z-1);
+                    }
+
+                    if(X<Max[0])
+                    {
+                        const size_t Other=Word+WordsPerZ;
+                        Missing=(Rock^RockWords[Other])&Valid
+                            &~(Candidates&CandidateWords[Other]);
+                        while(Missing)
+                        {
+                            const uint32 Bit=std::countr_zero(Missing);Missing&=Missing-1;
+                            const int32 Z=Min[2]+static_cast<int32>(W*64+Bit);
+                            EnsureDistance(X,Y,Z);
+                            EnsureDistance(X+1,Y,Z);
+                        }
+                    }
+                    if(Y<Max[1])
+                    {
+                        const size_t Other=Word+static_cast<size_t>(Size[0])*WordsPerZ;
+                        Missing=(Rock^RockWords[Other])&Valid
+                            &~(Candidates&CandidateWords[Other]);
+                        while(Missing)
+                        {
+                            const uint32 Bit=std::countr_zero(Missing);Missing&=Missing-1;
+                            const int32 Z=Min[2]+static_cast<int32>(W*64+Bit);
+                            EnsureDistance(X,Y,Z);
+                            EnsureDistance(X,Y+1,Z);
+                        }
+                    }
+                }
+            }
+            AddedTotal+=AddedThisPass;
+            if(!bSignChanged)break;
+        }
+        std::printf("[GridStairDistanceRepair] exact_endpoint_proxies=%llu occupancy_corrections=%llu\n",
+            static_cast<unsigned long long>(AddedTotal),
+            static_cast<unsigned long long>(SignCorrections));
+        return AddedTotal;
+    }
+
     void StoreSurfaceDistance(size_t Node,float Density)
     {
         int32 Q=static_cast<int32>(std::lround(Density*16.0f));

Standalone/Core/src/VoxelForgeCore.cpp

@@ -2,6 +2,12 @@
 #include "StandaloneSnapshotAdapter.h"
 #include "VoxelForgeCore/VoxelForgeCore.h"
 
+#include <shared_mutex>
+#include <mutex>
+#include <atomic>
+#include <unordered_map>
+#include <unordered_set>
+
 namespace vfcore::detail
 {
 #include "FarShellsInternal.h"
@@ -29,6 +35,40 @@ namespace VoxelForgeCore
         TileKey FromNative(const FVoxelTileKey& value)
         { return {{value.Coord.X,value.Coord.Y,value.Coord.Z},value.Level}; }
 
+        std::int32_t FloorDiv(std::int32_t value,std::int32_t divisor)
+        {
+            const std::int32_t quotient=value/divisor,remainder=value%divisor;
+            return quotient-((remainder!=0&&remainder<0)?1:0);
+        }
+
+        std::int32_t TilesPerShapePage(std::int32_t lod)
+        {
+            constexpr std::int32_t PageWidthVoxels=128;
+            return std::max(1,(PageWidthVoxels/CHUNK_SIZE)>>std::clamp(lod,0,30));
+        }
+
+        TileKey ShapePageKey(const TileKey& tile)
+        {
+            TileKey page=tile;
+            const std::int32_t span=TilesPerShapePage(tile.lod);
+            page.coordinate={FloorDiv(tile.coordinate.x,span),
+                FloorDiv(tile.coordinate.y,span),FloorDiv(tile.coordinate.z,span)};
+            return page;
+        }
+
+        bool CoveredByBaseShape(const ShapeBuildRequest& request,
+                                const WorldConfiguration& configuration,const TileKey& tile)
+        {
+            if(tile.lod<0||tile.lod>=configuration.fullResolutionLodCount)return false;
+            const FVoxelTileKey native=ToNative(tile);
+            const FIntVector origin=native.OriginVoxels();
+            const std::int32_t extent=native.ExtentVoxels();
+            for(std::int32_t axis=0;axis<3;++axis)
+                if((&origin.X)[axis]<(&request.minVoxel.x)[axis]
+                    ||(&origin.X)[axis]+extent>(&request.maxVoxel.x)[axis])return false;
+            return true;
+        }
+
         WorldConfiguration MakeConfiguration(const FStandaloneOwnerWorld& owner)
         {
             WorldConfiguration out;
@@ -233,6 +273,10 @@ namespace VoxelForgeCore
         std::shared_ptr<FStandaloneOwnerWorld> owner;
         WorldConfiguration configuration;
         std::unique_ptr<FStandaloneShapeWorld> shape;
+        ShapeBuildRequest buildRequest;
+        mutable std::shared_mutex tileRegionMutex;
+        std::unordered_map<TileKey,std::shared_ptr<FStandaloneShapeWorld>,TileKeyHash> tileRegions;
+        std::atomic<std::size_t> tileRegionCount{0};
         std::vector<FStandaloneShapeWorld::FEditBrush> editLog;
         std::map<std::uint64_t,EditResult> transactions;
         bool hasLastSequence=false;
@@ -259,10 +303,88 @@ namespace VoxelForgeCore
             ToNative(request.clipMinVoxel),ToNative(request.clipMaxVoxel),
             static_cast<int32>(std::clamp<std::uint32_t>(request.workerLimit,1,8)),ToNative(request.detail),
             request.includeFarWorld,error,&scheduler,request.roundTunnels,request.profileDetailBand);
-        if(ok)impl_->shape=std::move(shape);
+        if(ok)
+        {
+            impl_->shape=std::move(shape);
+            impl_->buildRequest=request;
+            std::unique_lock lock(impl_->tileRegionMutex);
+            impl_->tileRegions.clear();
+            impl_->tileRegionCount.store(0,std::memory_order_release);
+        }
         return ok;
     }
 
+    bool World::compileTileRegion(std::span<const TileKey> tiles,std::uint32_t workerLimit,
+                                  const JobScheduler& scheduler,std::string& error,
+                                  std::size_t* outCompiledTiles)
+    {
+        if(outCompiledTiles)*outCompiledTiles=0;
+        if(!impl_||!impl_->owner||!impl_->shape||!impl_->shape->IsBuilt())
+        {error="the base world must be compiled before adding tile regions";return false;}
+        if(tiles.empty())return true;
+
+        std::unordered_map<TileKey,std::vector<TileKey>,TileKeyHash> pendingPages;
+        pendingPages.reserve(tiles.size());
+        {
+            std::shared_lock lock(impl_->tileRegionMutex);
+            for(const TileKey& key:tiles)
+            {
+                if(key.lod<0||key.lod>8)
+                {error="tile region contains an invalid LOD";return false;}
+                if(key.lod>=impl_->configuration.fullResolutionLodCount
+                    ||CoveredByBaseShape(impl_->buildRequest,impl_->configuration,key))continue;
+                const TileKey pageKey=ShapePageKey(key);
+                if(!impl_->tileRegions.contains(pageKey))pendingPages[pageKey].push_back(key);
+            }
+        }
+        if(pendingPages.empty())return true;
+
+        std::size_t compiledTileCount=0;
+        for(const auto& [pageKey,requestedTiles]:pendingPages)
+        {
+            const std::int32_t tileCount=TilesPerShapePage(pageKey.lod);
+            const std::int32_t tileExtent=CHUNK_SIZE<<pageKey.lod;
+            const FIntVector pageMin(pageKey.coordinate.x*tileCount*tileExtent,
+                pageKey.coordinate.y*tileCount*tileExtent,
+                pageKey.coordinate.z*tileCount*tileExtent);
+            const FIntVector pageMax(pageMin.X+tileCount*tileExtent,
+                pageMin.Y+tileCount*tileExtent,pageMin.Z+tileCount*tileExtent);
+            constexpr std::int32_t PagePad=8;
+            const FIntVector fineMin(pageMin.X-PagePad,pageMin.Y-PagePad,pageMin.Z-PagePad);
+            const FIntVector fineMax(pageMax.X+PagePad,pageMax.Y+PagePad,pageMax.Z+PagePad);
+
+            auto page=std::make_shared<FStandaloneShapeWorld>();
+            const ShapeBuildRequest& base=impl_->buildRequest;
+            if(!page->Build(*impl_->owner,fineMin,fineMax,pageMin,pageMax,
+                static_cast<int32>(std::clamp<std::uint32_t>(workerLimit,1,8)),
+                ToNative(base.detail),false,error,&scheduler,
+                base.roundTunnels,base.profileDetailBand))return false;
+            if(!impl_->editLog.empty())page->SetEditTransaction(impl_->editLog);
+
+            {
+                std::unique_lock lock(impl_->tileRegionMutex);
+                impl_->tileRegions.try_emplace(pageKey,std::move(page));
+                impl_->tileRegionCount.store(impl_->tileRegions.size(),std::memory_order_release);
+            }
+            compiledTileCount+=requestedTiles.size();
+        }
+        if(outCompiledTiles)*outCompiledTiles=compiledTileCount;
+        return true;
+    }
+
+    void World::retainTileRegions(std::span<const TileKey> desiredTiles)
+    {
+        if(!impl_)return;
+        std::unordered_set<TileKey,TileKeyHash> desired;
+        desired.reserve(desiredTiles.size()*2+1);
+        for(const TileKey& key:desiredTiles)
+            if(key.lod>=0&&key.lod<impl_->configuration.fullResolutionLodCount)
+                desired.insert(ShapePageKey(key));
+        std::unique_lock lock(impl_->tileRegionMutex);
+        std::erase_if(impl_->tileRegions,[&](const auto& entry){return !desired.contains(entry.first);});
+        impl_->tileRegionCount.store(impl_->tileRegions.size(),std::memory_order_release);
+    }
+
     void World::buildFarWorld()
     { if(impl_->shape)impl_->shape->BuildFarWorld(); }
     bool World::isCompiled() const noexcept { return impl_&&impl_->shape&&impl_->shape->IsBuilt(); }
@@ -357,9 +479,17 @@ namespace VoxelForgeCore
         if(!impl_||!impl_->owner||!impl_->shape||!impl_->shape->IsBuilt())
         { error="world must be compiled before generating tiles";return std::nullopt; }
         const auto& world=*impl_->owner;
+        std::shared_ptr<FStandaloneShapeWorld> page;
+        if(impl_->tileRegionCount.load(std::memory_order_acquire)!=0)
+        {
+            std::shared_lock lock(impl_->tileRegionMutex);
+            if(const auto found=impl_->tileRegions.find(ShapePageKey(key));found!=impl_->tileRegions.end())
+                page=found->second;
+        }
+        const FStandaloneShapeWorld& tileShape=page?*page:*impl_->shape;
         UVoxelMarchingCubesMesher mesher;
         mesher.SetGenerator(world.Generator.get());
-        mesher.SetStandaloneShapeWorld(impl_->shape.get());
+        mesher.SetStandaloneShapeWorld(&tileShape);
         mesher.bStandaloneSkipUvAndColors=options.skipUvAndColors;
         mesher.bStandaloneSkipUV=options.skipUv;mesher.bStandaloneSkipColors=options.skipColors;
         mesher.bStandaloneSkipMaterialGroups=options.skipMaterialGroups;
@@ -374,10 +504,11 @@ namespace VoxelForgeCore
         FVoxelMeshData mesh=mesher.GenerateMesh(origin,step,cells,nullptr,
             options.bandMinZVoxel,options.bandMaxZVoxel,&sampleCount,nullptr,nullptr,
             (options.hashDensity||options.captureDensitySamples)?&densityValues:nullptr);
-        if(impl_->shape->HasFarWorld())
+        const FStandaloneShapeWorld& farShape=tileShape.HasFarWorld()?tileShape:*impl_->shape;
+        if(farShape.HasFarWorld())
         {
-            AppendFarStratumShells(world,*impl_->shape,nativeKey,step,mesh);
-            AppendFarConnectorShells(*impl_->shape,nativeKey,step,world.CoarseTileCells,mesh);
+            AppendFarStratumShells(world,farShape,nativeKey,step,mesh);
+            AppendFarConnectorShells(farShape,nativeKey,step,world.CoarseTileCells,mesh);
         }
 
         TileMesh out;out.key=key;out.densitySampleCount=static_cast<std::uint64_t>(std::max<int64>(0,sampleCount));
@@ -451,6 +582,11 @@ namespace VoxelForgeCore
         }
         impl_->editLog.insert(impl_->editLog.end(),native.begin(),native.end());
         impl_->shape->SetEditTransaction(impl_->editLog);
+        {
+            std::shared_lock lock(impl_->tileRegionMutex);
+            for(const auto& [key,page]:impl_->tileRegions)
+                if(page)page->SetEditTransaction(impl_->editLog);
+        }
         const FIntVector min=impl_->shape->GetEditBoundsMin(),max=impl_->shape->GetEditBoundsMax();
         EditResult result;result.digest=digest;
         result.affectedByLod.resize(static_cast<std::size_t>(std::max(impl_->configuration.maxLod,0)+1));
@@ -487,6 +623,8 @@ namespace VoxelForgeCore
     }
 
     bool World::auditDetailPassing() const { return impl_&&impl_->shape&&impl_->shape->IsDetailAuditPassing(); }
+    bool World::auditGridStairIntegrity() const
+    { return impl_&&impl_->shape&&impl_->shape->AuditGridStairIntegrity(); }
     bool World::auditSurfaceFamilies(bool passageOnly) const
     { return impl_&&impl_->shape&&impl_->shape->AuditSurfaceBandFamilies(passageOnly); }
     bool World::auditViewSurface(Vec3d camera,double yaw,double pitch) const