wip(assembler): round L18 -- FloatingIslands false floors removed; shared strate ceiling

FI geometry v3 drops the all-XY lower boundary seal that created false floors (3.5/8 m); the
ceiling comes from the shared VF_ApplyUpperBoundarySeal and AppendStratumBoundaryCeilings path
for every generator, at each strate's own configured upper boundary (owner: every strate has a
ceiling). Far-LOD ceiling continuity: 0 gaps at LOD4-8. SurfaceWorld bit-identical to L14
(14 configs + 24 m crossing); FI deterministic (28-row matrix); route parity and proofs pass.
Unreal: FI geometryVersion 2->3 and the shared upper-seal helper extracted (UBT compile needed on
the owner PC). Open: small ceiling holes; lower-stratum LOD ring steps seen through the FI void.

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

Source/VoxelForge/Private/VoxelForgeCoreAdapter.cpp

@@ -450,7 +450,7 @@ bool BuildFloatingIslandStratumPlan(const UVoxelStrateManager* StrateManager,
     IslandPlan.topChunkZ = Slot.TopChunkZ;
     IslandPlan.bottomChunkZ = Slot.BottomChunkZ;
     auto& Recipe = IslandPlan.manifest.recipe;
-    Recipe.geometryVersion = 2;
+    Recipe.geometryVersion = 3;
     Recipe.seed = static_cast<std::uint32_t>(StrateManager->GetWorldSeed());
     Recipe.ownerVoxelSizeMicrons = static_cast<std::uint32_t>(std::llround(OwnerVoxelSizeCm * 10000.0));
     Recipe.coreVoxelSizeMicrons = static_cast<std::uint32_t>(std::llround(CoreVoxelSizeCm * 10000.0));

Source/VoxelForge/Public/VoxelDensityPrimitives.h

@@ -41,21 +41,27 @@
 // SealFactor > 0 et BaseDensity > 0, le résultat est solide GARANTI quelle qu'ait été l'entrée.
 // C'est exactement ce qu'encode `IVoxelDensityOp::ClassifyBox` (voir VoxelDensityOp.h), et la
 // raison pour laquelle cette méthode existe.
-FORCEINLINE void VF_ApplyBoundarySeal(float& Density, float WorldZ,
-    float StrateTopZ, float StrateBottomZ,
-    float Thickness, float BaseDensity)
+FORCEINLINE void VF_ApplyUpperBoundarySealValue(float& Density, float WorldZ,
+    float StrateTopZ, float Thickness, float BaseDensity)
 {
-    if (VoxelDensityAblation::IsBoundarySealOff() || Thickness <= 0.0f) return;
-
-    const float DistTop = StrateTopZ - WorldZ;     // + si on est sous le plafond
-    const float DistBot = WorldZ - StrateBottomZ;  // + si on est au-dessus du sol
-
+    const float DistTop = StrateTopZ - WorldZ;
     if (DistTop >= 0.0f && DistTop < Thickness)
     {
         float SealFactor = 1.0f - (DistTop / Thickness);
         SealFactor = SmoothStep01(SealFactor);
         Density = FMath::Max(Density, SealFactor * BaseDensity);
     }
+}
+
+FORCEINLINE void VF_ApplyBoundarySeal(float& Density, float WorldZ,
+    float StrateTopZ, float StrateBottomZ,
+    float Thickness, float BaseDensity)
+{
+    if (VoxelDensityAblation::IsBoundarySealOff() || Thickness <= 0.0f) return;
+
+    const float DistBot = WorldZ - StrateBottomZ;  // + si on est au-dessus du sol
+
+    VF_ApplyUpperBoundarySealValue(Density, WorldZ, StrateTopZ, Thickness, BaseDensity);
     if (DistBot >= 0.0f && DistBot < Thickness)
     {
         float SealFactor = 1.0f - (DistBot / Thickness);
@@ -64,6 +70,16 @@ FORCEINLINE void VF_ApplyBoundarySeal(float& Density, float WorldZ,
     }
 }
 
+// The same structural seal, limited to a strate's upper boundary. Native finite fields use this
+// when their lower boundary intentionally has no seal; keeping the math here makes that ceiling
+// use the same shared density primitive as every two-sided strate seal.
+FORCEINLINE void VF_ApplyUpperBoundarySeal(float& Density, float WorldZ,
+    float StrateTopZ, float Thickness, float BaseDensity)
+{
+    if (VoxelDensityAblation::IsBoundarySealOff() || Thickness <= 0.0f) return;
+    VF_ApplyUpperBoundarySealValue(Density, WorldZ, StrateTopZ, Thickness, BaseDensity);
+}
+
 //=============================================================================
 // CARVE DE PASSAGE / PASSAGE CARVING
 //=============================================================================