wip(unreal): round 3 -- owner's in-game defects classified; opening room fixed; Core biome query

Luna, integration round 3, from the owner's four in-game screenshots:
- Capsule rings at the opening and the shaft continuing through the cave room were Core
  world defects: the synthetic bore is removed and the opening gets a finite origin room
  and floor (solid below). New world version, W1/W8/W16 identical: density
  a8bcb72d41092503, mesh 90f29ba15e24579f, payload 82c6b489e7bb7fd7, topology
  7b99448a1f844f2c.
- B-side landing and surface: headless coverage found no missing tiles or LOD-transition
  gaps (960 / 640 fine tiles compiled after travel); best explained by Core's missing
  SurfaceWorld representation. Null-RHI cannot rule out a presentation-only issue.
- Core mode GetBiomeAtWorldLocation now answers (e.g. Biome_Surface_Plain); biome
  terrain itself is not generated yet (proposal: native Core SurfaceWorld evaluator).
Owner checked the Step29 viewer himself: the surface strate type is absent there too.

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

Standalone/Core/src/ShapeWorldInternal.h

@@ -2502,6 +2502,10 @@ private:
                 AddEllipsoid(Center,{std::max(2.0f,C.Radius),std::max(2.0f,C.Radius),HalfZ},
                     {1,0,0},{0,1,0},{0,0,1},false);
             }
+
+            // Reproduce the owner's finite, top-anchored origin room in every strate.
+            // Reproduire dans chaque strate la salle d'origine finie et ancrée en haut.
+            AddOriginLandingRoom(FieldForStrate(Slot.StrateIndex));
         }
         const double PassageJoinBlend=ActiveBlendRadius;ActiveBlendRadius=JoinBlendRadius;
         ActiveFloorBlendRadius=FloorClipBlendRadius;
@@ -2633,17 +2637,63 @@ private:
             AddLanding(P.LowerLanding,true);
         }
         ActiveBlendRadius=PassageJoinBlend;ActiveFloorBlendRadius=0.0;
-        if(Owner->Settings->bOpenSurfaceEntry)
+    }
+
+    const FLayerField* FieldForStrate(int32 StrateIndex) const
+    {
+        for(const FLayerField& Field:LayerFields)
+            if(Field.StrateIndex==StrateIndex)return &Field;
+        return nullptr;
+    }
+
+    void AddOriginLandingRoom(const FLayerField* Field)
+    {
+        if(Field==nullptr||Owner==nullptr||Owner->Settings==nullptr)return;
+        const double Radius=Owner->Settings->OriginSpineRadius;
+        if(!(Radius>0.0)||!std::isfinite(Radius))return;
+
+        // These constants mirror VoxelPassageGeometry in legacy voxel units.
+        // Ces constantes reprennent VoxelPassageGeometry en voxels historiques.
+        constexpr double MinimumHalfWidth=12.0;
+        constexpr double MinimumRoomHeight=24.0;
+        constexpr double PlayerHeight=14.08;
+        constexpr double Headroom=8.0;
+        constexpr double FloorThickness=6.0;
+        constexpr double SealSafetyMargin=8.0;
+        constexpr double RoomRounding=3.0;
+        constexpr double ShaftFloorClearance=8.0;
+
+        const double SafeRadius=std::max(std::abs(Radius),2.0);
+        const double HalfWidth=std::max({MinimumHalfWidth,SafeRadius+4.0,
+            SafeRadius+ShaftFloorClearance});
+        const double DesiredHeight=std::max({MinimumRoomHeight,PlayerHeight+Headroom,
+            2.0*SafeRadius+4.0});
+        const double Seal=std::max(0.0,static_cast<double>(Field->Params.BoundarySealThickness));
+        const double InnerBottom=static_cast<double>(Field->Lo)+Seal;
+        const double InnerTop=static_cast<double>(Field->Hi)-Seal;
+        const double MinimumFloor=InnerBottom+FloorThickness+SealSafetyMargin;
+        const double MaximumFloor=InnerTop-DesiredHeight-SealSafetyMargin;
+        if(!(InnerTop>InnerBottom)||MaximumFloor<MinimumFloor)return;
+
+        const double FloorZ=MaximumFloor;
+        const double CeilingZ=FloorZ+DesiredHeight;
+        const double HalfZ=(CeilingZ-FloorZ)*0.5;
+        const double HalfExtent=std::max(HalfWidth-RoomRounding,0.5);
+        const double RoundedHalfZ=std::max(HalfZ-RoomRounding,0.5);
+        const size_t Before=Primitives.size();
+        AddRoundedBox(FVector(0,0,(FloorZ+CeilingZ)*0.5),
+            {HalfExtent,HalfExtent,RoundedHalfZ},RoomRounding,true);
+        for(size_t I=Before;I<Primitives.size();++I)
         {
-            const double Radius=std::max(8.0f,Owner->Settings->OriginSpineRadius);
-            const double Top=LayerRanges[0].Hi;
-            const FVector A(0,0,Top),B(0,0,std::max<double>(LayerRanges[0].Lo,Top-256.0));
-            AddCapsule(A,B,static_cast<float>(Radius),true);
+            // Keep the authored room floor hard and level while leaving all lower seal rock intact.
+            // Garder un sol horizontal net et préserver la roche du joint inférieur.
+            ApplyFloorClip(Primitives[I],FloorZ+0.5,0.0,0.0,0.0);
         }
     }
 
     void AddLanding(const FVoxelPassageLanding& L,bool bCritical=false)
     {
+        if(!(L.HalfWidth>0.0f)||!(L.CeilingZ>L.FloorZ))return;
         const double HalfZ=std::max(2.0,(L.CeilingZ-L.FloorZ)*0.5);
         const FVector Center(L.StandingPoint.X,L.StandingPoint.Y,(L.CeilingZ+L.FloorZ)*0.5);
         const double Width=std::max(6.0f,L.HalfWidth);