wip(assembler): round L36 -- tunnel floor without washboard; FI mouth without shards (evaluator v23)

The walk tread was built per segment as a one-sided density clamp, so its crossing with the native
field moved at segment joins (L35: 2.25-2.48 cm washboard). Treads now overlap up to 2 m as bounded
signed-distance slabs (0.06 cm residual). The FI mouth's crater detail and tread met without a smooth
join; v23 filters the local field, drops thin isolated solids and smooth-unions the tread with the
terrain. New floor ripple and mouth fragment/crease audits with L35 as failing controls. 24/24
passage rows, 30/30 determinism, 16/16 invariants, LOD0-8 rings; cost within noise.

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

Standalone/Core/src/ShapeWorldInternal.h

@@ -727,8 +727,9 @@ public:
                 }
             if(routeCount<2)return;
             const std::size_t lastSegment=routeCount-1;
-            const double floorThickness=1000000.0/std::max<std::uint32_t>(1,
-                ResolvedLayout->coreVoxelSizeMicrometres);
+            constexpr double MouthSupportBlendMetres=1.5;
+            const double mouthBlendWidth=MouthSupportBlendMetres*qPerMetre;
+            double mouthSupportDistance=std::numeric_limits<double>::infinity();
             for(std::size_t index=0;index<lastSegment;++index)
             {
                 const auto& a=*route[index];const auto& b=*route[index+1];
@@ -743,12 +744,25 @@ public:
                     ?a.values[3]+t*(static_cast<double>(b.values[3])-a.values[3]):0.0;
                 const double halfWidth=std::max(0.75*qPerMetre,routeRadius);
                 const double horizontalX=qx-centerX,horizontalY=qy-centerY;
-                if(horizontalX*horizontalX+horizontalY*horizontalY>halfWidth*halfWidth)continue;
-                const double floorVoxels=(centerZ-1.20*qPerMetre)/Q;
-                if(Z<floorVoxels-floorThickness||Z>floorVoxels+1.0/Q)continue;
-                composed=std::min(composed,static_cast<float>(
-                    std::clamp(Z-floorVoxels,-floorThickness,0.0)));
+                const double horizontalDistance=DeterministicSqrt(
+                    horizontalX*horizontalX+horizontalY*horizontalY);
+                const double floorQ=centerZ-1.20*qPerMetre;
+                const double sideDistance=horizontalDistance-halfWidth;
+                const double topDistance=qz-floorQ;
+                const double bottomDistance=floorQ-qPerMetre-qz;
+                const double verticalDistance=std::max(topDistance,bottomDistance);
+                if(sideDistance>mouthBlendWidth||verticalDistance>mouthBlendWidth)continue;
+                const double outside=DeterministicSqrt(
+                    std::max(sideDistance,0.0)*std::max(sideDistance,0.0)
+                    +std::max(verticalDistance,0.0)*std::max(verticalDistance,0.0));
+                const double inside=std::min(std::max(sideDistance,verticalDistance),0.0);
+                const double signedDistance=outside+inside;
+                mouthSupportDistance=std::min(mouthSupportDistance,signedDistance);
             }
+            if(std::isfinite(mouthSupportDistance))
+                composed=SmoothMinDistance(composed,
+                    static_cast<float>(mouthSupportDistance/Q),
+                    static_cast<float>(mouthBlendWidth/Q));
         };
         // Keep the native surface route connected to the entrance. Passage carving
         // then removes only the parts that overlap the tunnel, whose own tread owns
@@ -765,6 +779,19 @@ public:
         {
             const auto& passage=ResolvedLayout->passages[passageIndex];
             if(passage.controlPoints.size()<2)continue;
+            const auto supportStratum=[&](std::int32_t strateIndex)
+                ->const VoxelForgeCore::ResolvedLayoutStratumV2*
+            {
+                const auto it=std::find_if(ResolvedLayout->strates.begin(),
+                    ResolvedLayout->strates.end(),[strateIndex](const auto& stratum)
+                        {return stratum.strateIndex==strateIndex;});
+                return it==ResolvedLayout->strates.end()?nullptr:&*it;
+            };
+            const auto* supportUpper=supportStratum(passage.upperStrateIndex);
+            const auto* supportLower=supportStratum(passage.lowerStrateIndex);
+            const bool surfaceToTunnelSupport=supportUpper&&supportLower
+                &&supportUpper->generatorKind=="SurfaceWorld"
+                &&supportLower->generatorKind=="TunnelNetwork";
             const double firstFloorQ=passage.controlPoints.front().positionSubvoxels[2]
                 -passage.controlPoints.front().radiusSubvoxels+playerCenterAboveFloorQ;
             const double lastFloorQ=passage.controlPoints.back().positionSubvoxels[2]
@@ -880,7 +907,20 @@ public:
             std::ptrdiff_t bestScanIndex=std::numeric_limits<std::ptrdiff_t>::max();
             std::ptrdiff_t bestSupportSegmentIndex=0;
             bool hasSupportFloor=false;
-            double bestSupportDensity=0.0;
+            double bestSupportDistanceSquared=std::numeric_limits<double>::infinity();
+            double bestSupportDensity=std::numeric_limits<double>::infinity();
+            double bestSupportFloorQ=0.0;
+            bool bestSupportUsesSignedDistance=false;
+            std::ptrdiff_t selectedSupportSegmentIndex=-1;
+            const double lowerMouthDx=qx-passage.lowerMouthSubvoxels[0];
+            const double lowerMouthDy=qy-passage.lowerMouthSubvoxels[1];
+            const double lowerMouthDz=qz-passage.lowerMouthSubvoxels[2];
+            const double lowerMouthDistance=DeterministicSqrt(
+                lowerMouthDx*lowerMouthDx+lowerMouthDy*lowerMouthDy
+                    +lowerMouthDz*lowerMouthDz)/qPerMetre;
+            const double lowerMouthT=std::clamp((20.0-lowerMouthDistance)/12.0,0.0,1.0);
+            const double lowerMouthBlend=lowerMouthT*lowerMouthT
+                *(3.0-2.0*lowerMouthT);
             const auto considerCarveSegment=[&](std::size_t segmentIndex,int scanPhase)
             {
                 const std::ptrdiff_t index=static_cast<std::ptrdiff_t>(segmentIndex);
@@ -992,7 +1032,7 @@ public:
                     /distanceToCenter,0.0,1.0):0.0;
             const float relief=VF_FieldPassageWallRelief(static_cast<float>(X),static_cast<float>(Y),
                 static_cast<float>(Z),static_cast<std::uint32_t>(Owner?Owner->Seed:0));
-            const double wallReliefWeight=1.0-0.80*verticalWallAlignment;
+            const double wallReliefWeight=0.05+0.95*(1.0-verticalWallAlignment);
             const double roughSignedDistance=bestSignedDistance
                 +static_cast<double>(std::clamp(relief,-1.0f,1.0f))*0.21*qPerMetre*wallReliefWeight;
             if(IsPassageShortSpanSegment(passageIndex,static_cast<std::size_t>(bestIndex)))
@@ -1004,38 +1044,48 @@ public:
             // Positive density is air; rough rock is cut with full side/ceiling detail and
             // gentler relief on the gravity-facing wall so the supported tread stays open.
             composed=std::max(composed,static_cast<float>(-roughSignedDistance/Q));
-            double bestSupportDistanceSquared=std::numeric_limits<double>::infinity();
             const auto considerSupportSegment=[&](std::ptrdiff_t index)
             {
                 const auto& segmentA=passage.controlPoints[static_cast<std::size_t>(index)];
                 const auto& segmentB=passage.controlPoints[static_cast<std::size_t>(index+1)];
                 const double dx=static_cast<double>(segmentB.positionSubvoxels[0])-segmentA.positionSubvoxels[0];
                 const double dy=static_cast<double>(segmentB.positionSubvoxels[1])-segmentA.positionSubvoxels[1];
+                const double dz=static_cast<double>(segmentB.positionSubvoxels[2])-segmentA.positionSubvoxels[2];
                 const double radiusA=segmentA.radiusSubvoxels;
                 const double radiusB=segmentB.radiusSubvoxels;
                 const bool entryMouthShoulder=index<=2;
                 // Keep the tread within the probe band and below the capsule's
                 // lowest sampled point.
-                const double floorOffset=IsPassageShortSpanSegment(passageIndex,
+                const bool bridgeDeck=IsPassageShortSpanSegment(passageIndex,
                     static_cast<std::size_t>(index))
-                    ||IsPassageColumnSegment(passageIndex,static_cast<std::size_t>(index))
+                    ||IsPassageColumnSegment(passageIndex,static_cast<std::size_t>(index));
+                // Keep a small capsule margin at regular treads and restore most of
+                // the nominal height smoothly as a tread approaches its landing.
+                double floorOffset=bridgeDeck
                     ?PassageBridgeDeckOffsetMetres(passageIndex,static_cast<std::size_t>(index))
-                    :0.20;
+                    :std::lerp(0.15,0.20,lowerMouthBlend);
                 const double horizontalLengthSq=dx*dx+dy*dy;
+                const bool overlapSupportJoin=index+12<lastIndex
+                    &&!IsPassageShortSpanSegment(passageIndex,static_cast<std::size_t>(index))
+                    &&(index==0||(!IsPassageShortSpanSegment(passageIndex,
+                        static_cast<std::size_t>(index-1))));
+                const bool smoothSupportJoin=index>0&&overlapSupportJoin
+                    &&!IsPassageShortSpanSegment(passageIndex,static_cast<std::size_t>(index+1));
+                const double projection=horizontalLengthSq>0.0
+                    ?((qx-segmentA.positionSubvoxels[0])*dx
+                        +(qy-segmentA.positionSubvoxels[1])*dy)/horizontalLengthSq:bestT;
+                // Extend tread segments by a fixed distance through route knots. A
+                // fractional extension made the support width change with segment length.
+                const double overlapFraction=overlapSupportJoin&&horizontalLengthSq>0.0
+                ?std::min(0.5,2.0*qPerMetre/DeterministicSqrt(horizontalLengthSq)):0.0;
                 const double supportT=horizontalLengthSq>0.0
-                    ?std::clamp(((qx-segmentA.positionSubvoxels[0])*dx
-                        +(qy-segmentA.positionSubvoxels[1])*dy)/horizontalLengthSq,0.0,1.0)
-                    :bestT;
+                    ?std::clamp(projection,-overlapFraction,1.0+overlapFraction):bestT;
                 const double centerX=segmentA.positionSubvoxels[0]+supportT*dx;
                 const double centerY=segmentA.positionSubvoxels[1]+supportT*dy;
                 double centerZ=segmentA.positionSubvoxels[2]+supportT*(
                     static_cast<double>(segmentB.positionSubvoxels[2])-segmentA.positionSubvoxels[2]);
                 double radius=segmentA.radiusSubvoxels+supportT*(
                     static_cast<double>(segmentB.radiusSubvoxels)-segmentA.radiusSubvoxels);
-                const bool smoothSupportJoin=index>0&&index+12<lastIndex
-                    &&!IsPassageShortSpanSegment(passageIndex,static_cast<std::size_t>(index-1))
-                    &&!IsPassageShortSpanSegment(passageIndex,static_cast<std::size_t>(index))
-                    &&!IsPassageShortSpanSegment(passageIndex,static_cast<std::size_t>(index+1));
                 if(smoothSupportJoin)
                 {
                     const auto& p0=passage.controlPoints[static_cast<std::size_t>(index-1)];
@@ -1063,7 +1113,15 @@ public:
                 // Support belongs just below the avatar's foot plane. Queries within
                 // the capsule body, or a neighbouring coil's overlapping bore, must
                 // not turn that tread into a ceiling or mid-air shelf.
-                if(supportQueryDepth<0.93*qPerMetre||supportQueryDepth>1.30*qPerMetre)return;
+                // Sparse authored routes use the full signed distance around the top;
+                // dense routes retain the legacy one-sided tread density.
+                const double supportSegmentLength=DeterministicSqrt(
+                    horizontalLengthSq+dz*dz)/qPerMetre;
+                const bool sparseRouteSupport=supportSegmentLength>1.5;
+                const double minimumSupportQueryDepth=index==selectedSupportSegmentIndex
+                    &&sparseRouteSupport?0.65:0.93;
+                if(supportQueryDepth<minimumSupportQueryDepth*qPerMetre
+                    ||supportQueryDepth>1.30*qPerMetre)return;
                 const bool fallbackSupport=qz>=supportPlayerCenterZ-1.50*qPerMetre;
                 const double supportThicknessVoxels=fallbackSupport
                     ?qPerMetre/Q:0.5*qPerMetre/Q;
@@ -1072,12 +1130,8 @@ public:
                 // capsule on the neighbouring turn.
                 const bool lowerMouthBodyOverlap=index>=lowerMouthIndex-2
                     &&supportQueryDepth<0.98*qPerMetre;
-                const double supportEdgeNoise=entryMouthShoulder?std::clamp(
-                    static_cast<double>(VF_FieldPassageGroundGrain(static_cast<float>(X),
-                        static_cast<float>(Y),
-                        static_cast<std::uint32_t>(Owner?Owner->Seed:0))),-1.0,1.0):0.0;
                 const double supportHalfWidthMetres=lowerMouthBodyOverlap?0.90
-                    :entryMouthShoulder?1.20+0.20*supportEdgeNoise:1.25;
+                    :entryMouthShoulder?1.20:1.25;
                 const double supportHalfWidth=std::min(radius,
                     supportHalfWidthMetres*qPerMetre);
                 // Keep the walk core within a 0.50 m span with shallow relief, then
@@ -1095,30 +1149,50 @@ public:
                 const double localSupportThicknessVoxels=entryMouthShoulder
                     ?supportThicknessVoxels*(1.0-0.72*supportEdgeSmooth)
                     :supportThicknessVoxels;
-                const double supportEdgeDepth=entryMouthShoulder
-                    ?0.35+0.15*supportEdgeNoise:0.35;
+                constexpr double supportEdgeDepth=0.35;
                 const double floorQ=centerZ-radius+floorOffset*qPerMetre
-                    +supportEdgeNoise*(horizontalDistance>0.60*qPerMetre
-                        ?0.35:0.14)*qPerMetre
                     -supportEdgeSmooth*supportEdgeDepth*qPerMetre;
                 const double floorVoxels=floorQ/Q;
-                if(Z<floorVoxels-localSupportThicknessVoxels||Z>floorVoxels+1.0/Q)return;
+                const double supportPositiveRangeVoxels=sparseRouteSupport
+                    ?0.35*qPerMetre/Q:1.0/Q;
+                if(Z<floorVoxels-localSupportThicknessVoxels
+                    ||Z>floorVoxels+supportPositiveRangeVoxels)return;
                 if(horizontalDistance>supportHalfWidth)return;
-                const double supportDistanceSq=horizontalDistance*horizontalDistance
+                const double supportDistanceSquared=horizontalDistance*horizontalDistance
                     +(Z-floorVoxels)*(Z-floorVoxels);
-                if(supportDistanceSq>=bestSupportDistanceSquared)return;
-                bestSupportDistanceSquared=supportDistanceSq;
+                if(supportDistanceSquared>=bestSupportDistanceSquared)return;
+                bestSupportDistanceSquared=supportDistanceSquared;
                 hasSupportFloor=true;
                 bestSupportSegmentIndex=index;
-                bestSupportDensity=std::clamp(Z-floorVoxels,
-                    -localSupportThicknessVoxels,0.0);
+                if(sparseRouteSupport)
+                {
+                    // Sparse support profiles need both sides of a signed distance
+                    // so the sampled zero crossing stays on the tread top.
+                    const double topDistance=qz-floorQ;
+                    const double bottomDistance=floorQ-localSupportThicknessVoxels*Q-qz;
+                    const double verticalDistance=std::max(topDistance,bottomDistance);
+                    const double sideDistance=horizontalDistance-supportHalfWidth;
+                    const double outside=DeterministicSqrt(
+                        std::max(sideDistance,0.0)*std::max(sideDistance,0.0)
+                        +std::max(verticalDistance,0.0)*std::max(verticalDistance,0.0));
+                    const double inside=std::min(std::max(sideDistance,verticalDistance),0.0);
+                    bestSupportDensity=(outside+inside)/Q;
+                }
+                else
+                {
+                    bestSupportDensity=std::clamp(Z-floorVoxels,
+                        -localSupportThicknessVoxels,0.0);
+                }
+                bestSupportFloorQ=floorQ;
+                bestSupportUsesSignedDistance=sparseRouteSupport;
             };
             std::ptrdiff_t supportCenterIndex=bestIndex;
             if(bestIndex<lowerMouthIndex)
             {
                 // A helix can have multiple centerlines at one XY. Select the tread
                 // whose floor is just below this density query, not the closest wall.
-                const double supportProfileTarget=qz+0.93*qPerMetre;
+                const double supportProfileOffset=surfaceToTunnelSupport?1.13:0.93;
+                const double supportProfileTarget=qz+supportProfileOffset*qPerMetre;
                 const auto supportProfile=std::lower_bound(passage.controlPoints.begin(),mainEnd,
                     supportProfileTarget,[&](const auto& point,double value)
                         {return floorProfile(point)>value;});
@@ -1132,6 +1206,8 @@ public:
             const std::ptrdiff_t supportBegin=std::max<std::ptrdiff_t>(0,supportCenterIndex-1);
             const std::ptrdiff_t supportEnd=std::min<std::ptrdiff_t>(lastIndex-1,
                 supportCenterIndex+1);
+            selectedSupportSegmentIndex=supportCenterIndex>0
+                ?supportCenterIndex-1:supportCenterIndex;
             for(std::ptrdiff_t index=supportBegin;index<=supportEnd;++index)
                 considerSupportSegment(index);
             // Keep route treads inside the native rock envelope. Carving may reopen the
@@ -1142,13 +1218,24 @@ public:
             const bool shortSpanFloorSupport=hasSupportFloor
                 &&IsPassageShortSpanSegment(passageIndex,
                     static_cast<std::size_t>(bestSupportSegmentIndex));
-            const bool capsuleAllowsSupport=passageTileScopeMatches
+            const double capsuleClearanceMetres=bestSupportUsesSignedDistance?0.045:0.05;
+            const double capsuleQueryZ=bestSupportUsesSignedDistance?bestSupportFloorQ:qz;
+            const bool supportCapsuleProfileAvailable=passageIndex<PassageNearestNodes.size()
+                &&!PassageNearestNodes[passageIndex].empty();
+            const bool capsuleAllowsSupport=(passageTileScopeMatches
+                ||(bestSupportUsesSignedDistance&&supportCapsuleProfileAvailable))
                 ?!PassagePlayerCapsuleBlocksSupport(passageIndex,carveBegin,carveEnd,
-                    lowerMouthIndex,mouthSearchBegin,mouthSearchEnd,lastIndex,qx,qy,qz,qPerMetre)
-                :bestPlayerCapsuleSignedDistance>=0.05*qPerMetre;
+                    lowerMouthIndex,mouthSearchBegin,mouthSearchEnd,lastIndex,qx,qy,
+                    capsuleQueryZ,qPerMetre,capsuleClearanceMetres)
+                :bestPlayerCapsuleSignedDistance>=capsuleClearanceMetres*qPerMetre;
+            // Outside bridge and short-span segments, add the tread only where the
+            // native field already provides a solid envelope; the capsule check keeps
+            // that support below the player's walk space.
             if(hasSupportFloor&&(density<0.0f||passageColumnFloorSupport||shortSpanFloorSupport)
-                &&capsuleAllowsSupport)
+                &&(capsuleAllowsSupport||bestSupportDensity>=0.0))
+            {
                 composed=std::min(composed,static_cast<float>(bestSupportDensity));
+            }
         }
         return composed;
     }
@@ -2990,7 +3077,8 @@ private:
     }
 
     bool PassagePlayerCapsuleBlocksSupportNode(std::size_t passageIndex,int nodeIndex,
-        std::size_t first,std::size_t end,double qx,double qy,double qz,double qPerMetre) const
+        std::size_t first,std::size_t end,double qx,double qy,double qz,double qPerMetre,
+        double minimumClearanceMetres) const
     {
         if(passageIndex>=PassageNearestNodes.size()||nodeIndex<0)return false;
         const auto& nodes=PassageNearestNodes[passageIndex];
@@ -3026,26 +3114,26 @@ private:
                 const double vertical=std::max(0.0,std::abs(qz-centerZ)-0.54*qPerMetre);
                 const double distance=DeterministicSqrt(horizontalX*horizontalX+horizontalY*horizontalY
                     +vertical*vertical)-0.34*qPerMetre;
-                if(distance<0.05*qPerMetre)return true;
+                if(distance<minimumClearanceMetres*qPerMetre)return true;
             }
             return false;
         }
         return PassagePlayerCapsuleBlocksSupportNode(passageIndex,node.left,first,end,
-                qx,qy,qz,qPerMetre)
+                qx,qy,qz,qPerMetre,minimumClearanceMetres)
             ||PassagePlayerCapsuleBlocksSupportNode(passageIndex,node.right,first,end,
-                qx,qy,qz,qPerMetre);
+                qx,qy,qz,qPerMetre,minimumClearanceMetres);
     }
 
     bool PassagePlayerCapsuleBlocksSupport(std::size_t passageIndex,
         std::ptrdiff_t carveBegin,std::ptrdiff_t carveEnd,std::ptrdiff_t lowerMouthIndex,
         std::ptrdiff_t mouthSearchBegin,std::ptrdiff_t mouthSearchEnd,std::ptrdiff_t lastIndex,
-        double qx,double qy,double qz,double qPerMetre) const
+        double qx,double qy,double qz,double qPerMetre,double minimumClearanceMetres) const
     {
         const auto blocked=[&](std::ptrdiff_t first,std::ptrdiff_t last)
         {
             return first<=last&&PassagePlayerCapsuleBlocksSupportNode(passageIndex,0,
                 static_cast<std::size_t>(first),static_cast<std::size_t>(last+1),
-                qx,qy,qz,qPerMetre);
+                qx,qy,qz,qPerMetre,minimumClearanceMetres);
         };
         return blocked(carveBegin,carveEnd)
             ||blocked(0,std::min<std::ptrdiff_t>(8,lowerMouthIndex)-1)
@@ -4429,7 +4517,159 @@ private:
         const VoxelForgeCore::FloatingIslandFieldV1 Field(
             Plan->manifest.recipe,Plan->manifest.plan);
         if(!Field.isValid())return false;
-        std::int64_t Density=Field.densitySubvoxels(ToFixed(X),ToFixed(Y),ToFixed(Z));
+        const std::int64_t qx=ToFixed(X),qy=ToFixed(Y),qz=ToFixed(Z);
+        std::int64_t Density=Field.densitySubvoxels(qx,qy,qz);
+        // The anchor-root field keeps broad lobes, but its shortest authored noise
+        // wavelength is below one metre. Filter that detail only around a FloatingIslands
+        // passage mouth so Marching Cubes does not expose voxel-sized chips on the crater
+        // wall. The broad root profile is unchanged outside this local mouth envelope.
+        double mouthFilterWeight=0.0;
+        const double qToMetres=static_cast<double>(ResolvedLayout->coreVoxelSizeMicrometres)
+            /(static_cast<double>(VoxelForgeCore::WorldAssemblySubvoxelsPerVoxel)*1000000.0);
+        const double densityMetres=std::abs(static_cast<double>(Density))*qToMetres;
+        if(densityMetres<4.0)
+        {
+            bool foundPassageMouth=false;
+            for(const auto& passage:ResolvedLayout->passages)
+            {
+                if(passage.upperStrateIndex!=StrateIndex)continue;
+                foundPassageMouth=true;
+                const double dx=(static_cast<double>(qx)-passage.upperMouthSubvoxels[0])*qToMetres;
+                const double dy=(static_cast<double>(qy)-passage.upperMouthSubvoxels[1])*qToMetres;
+                const double dz=(static_cast<double>(qz)-passage.upperMouthSubvoxels[2])*qToMetres;
+                const double distance=std::sqrt(dx*dx+dy*dy+dz*dz);
+                constexpr double FilterCoreRadiusMetres=8.5;
+                constexpr double FilterOuterRadiusMetres=12.5;
+                const double fade=std::clamp((FilterOuterRadiusMetres-distance)
+                    /(FilterOuterRadiusMetres-FilterCoreRadiusMetres),0.0,1.0);
+                const double weight=fade*fade*(3.0-2.0*fade);
+                mouthFilterWeight=std::max(mouthFilterWeight,weight);
+            }
+            if(!foundPassageMouth)
+            {
+                // The passage-free native control retains the stratum route anchors.
+                // Use its terminal route point as the same local mouth filter origin so
+                // both native and composed fields receive the same root smoothing.
+                const auto stratum=std::find_if(ResolvedLayout->strates.begin(),
+                    ResolvedLayout->strates.end(),[StrateIndex](const auto& value)
+                        {return value.strateIndex==StrateIndex;});
+                if(stratum!=ResolvedLayout->strates.end())
+                {
+                    const VoxelForgeCore::ResolvedLayoutAnchorV2* terminal=nullptr;
+                    for(const auto& anchor:stratum->anchors)
+                        if(anchor.kind=="route_point"&&anchor.values.size()>=3)
+                            terminal=&anchor;
+                    if(terminal)
+                    {
+                        const double dx=static_cast<double>(qx-terminal->values[0])*qToMetres;
+                        const double dy=static_cast<double>(qy-terminal->values[1])*qToMetres;
+                        const double dz=static_cast<double>(qz-terminal->values[2])*qToMetres;
+                        const double distance=std::sqrt(dx*dx+dy*dy+dz*dz);
+                        constexpr double FilterCoreRadiusMetres=8.5;
+                        constexpr double FilterOuterRadiusMetres=12.5;
+                        const double fade=std::clamp((FilterOuterRadiusMetres-distance)
+                            /(FilterOuterRadiusMetres-FilterCoreRadiusMetres),0.0,1.0);
+                        mouthFilterWeight=fade*fade*(3.0-2.0*fade);
+                    }
+                }
+            }
+        }
+        if(mouthFilterWeight>0.0)
+        {
+            // Preserve the resolved walk route while filtering the passage and crater field.
+            const double queryX=static_cast<double>(qx)*qToMetres;
+            const double queryY=static_cast<double>(qy)*qToMetres;
+            const double queryZ=static_cast<double>(qz)*qToMetres;
+            const auto stratum=std::find_if(ResolvedLayout->strates.begin(),
+                ResolvedLayout->strates.end(),[StrateIndex](const auto& value)
+                    {return value.strateIndex==StrateIndex;});
+            if(stratum!=ResolvedLayout->strates.end())
+            {
+                const VoxelForgeCore::ResolvedLayoutAnchorV2* previous=nullptr;
+                for(const auto& anchor:stratum->anchors)
+                {
+                    if(anchor.kind!="route_point"||anchor.values.size()<3)continue;
+                    if(previous)
+                    {
+                        const double ax=static_cast<double>(previous->values[0])*qToMetres;
+                        const double ay=static_cast<double>(previous->values[1])*qToMetres;
+                        const double az=static_cast<double>(previous->values[2])*qToMetres;
+                        const double dx=(static_cast<double>(anchor.values[0])
+                            -previous->values[0])*qToMetres;
+                        const double dy=(static_cast<double>(anchor.values[1])
+                            -previous->values[1])*qToMetres;
+                        const double lengthSquared=dx*dx+dy*dy;
+                        const double t=lengthSquared>0.0?std::clamp(
+                            ((queryX-ax)*dx+(queryY-ay)*dy)/lengthSquared,0.0,1.0):0.0;
+                        const double centerX=ax+t*dx,centerY=ay+t*dy;
+                        const double centerZ=az+t*(static_cast<double>(anchor.values[2])
+                            -previous->values[2])*qToMetres;
+                        const double supportRadius=previous->values.size()>=4
+                            ?static_cast<double>(previous->values[3])*qToMetres:0.75;
+                        const double floorZ=centerZ-1.20;
+                        const double protectedRadius=supportRadius+0.75;
+                        if((queryX-centerX)*(queryX-centerX)
+                                +(queryY-centerY)*(queryY-centerY)
+                                <protectedRadius*protectedRadius
+                            &&std::abs(queryZ-floorZ)<1.25)
+                        {
+                            mouthFilterWeight=0.0;
+                            break;
+                        }
+                    }
+                    previous=&anchor;
+                }
+            }
+        }
+        if(mouthFilterWeight>0.0)
+        {
+            constexpr std::int64_t FilterStep=8*VoxelForgeCore::WorldAssemblySubvoxelsPerVoxel;
+            std::int64_t weightedSum=0;
+            for(int dz=-1;dz<=1;++dz)
+                for(int dy=-1;dy<=1;++dy)
+                    for(int dx=-1;dx<=1;++dx)
+                    {
+                        const std::int64_t weight=(dx==0?2:1)*(dy==0?2:1)*(dz==0?2:1);
+                        const std::int64_t sample=(dx==0&&dy==0&&dz==0)?Density:
+                            Field.densitySubvoxels(qx+dx*FilterStep,qy+dy*FilterStep,
+                                qz+dz*FilterStep);
+                        weightedSum+=sample*weight;
+                    }
+            // A separable [1,2,1]^3 kernel over a 2 m footprint filters sub-voxel
+            // root detail while retaining the signed field on both sides of the surface.
+            const double filtered=static_cast<double>(weightedSum)/64.0;
+            const std::int64_t filteredDensity=static_cast<std::int64_t>(std::llround(
+                std::lerp(static_cast<double>(Density),filtered,mouthFilterWeight)));
+            Density=filteredDensity;
+            // Marching Cubes can retain an isolated solid with no two-metre axis
+            // thickness as a handful of disconnected triangles. Remove only shallow
+            // negative samples surrounded by air at a one-metre probe distance; a
+            // walk floor or wall has solid material on at least one side of this test.
+            constexpr double FragmentProbeMetres=1.0;
+            const std::int64_t fragmentStep=static_cast<std::int64_t>(std::llround(
+                FragmentProbeMetres/qToMetres));
+            if(mouthFilterWeight>=0.25&&Density<0
+                &&static_cast<double>(-Density)*qToMetres<FragmentProbeMetres)
+            {
+                bool surroundedByAir=true;
+                std::int64_t minimumAirDensity=std::numeric_limits<std::int64_t>::max();
+                for(std::size_t axis=0;axis<3&&surroundedByAir;++axis)
+                    for(const int sign:{-1,1})
+                    {
+                        std::array<std::int64_t,3> sample{qx,qy,qz};
+                        sample[axis]+=sign*fragmentStep;
+                        const std::int64_t neighbor=Field.densitySubvoxels(
+                            sample[0],sample[1],sample[2]);
+                        if(neighbor<=0)
+                        {
+                            surroundedByAir=false;
+                            break;
+                        }
+                        minimumAirDensity=std::min(minimumAirDensity,neighbor);
+                    }
+                if(surroundedByAir)Density=std::max(Density,minimumAirDensity);
+            }
+        }
         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;