wip(assembler): round S4 -- continuous far ceiling at the strate's upper boundary

S3's far cap sat up to 8.2 m above the near roof and read as floating pieces.
The far render cap now projects onto the owning strate's upper boundary
(density unchanged), on a global XY lattice, LOD4 16-voxel grid + LOD5-8
128-voxel. Cap agreement 0.05 cm (100 cm control detected), 2520/2520 upward
rays hit roof on the owner walk. Far recipe v2; LOD0-3 hashes equal S2/S3.
Tile p95 flat; cold clipmap +4.4%. Far-cliff fluting left open (coarse MC step).

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

Standalone/Core/src/WorldAssemblerInternal.h

@@ -1463,8 +1463,9 @@ namespace world_assembly_detail
             +secondaryHeight*(65536-primaryWeight))/65536;
         out.biomeId=primary->stableId;out.neighborBiomeId=secondary->stableId;
         out.biomeWeightQ16=primaryWeight;
-        out.capHeightSubvoxels=plan.capHeightSubvoxels+MulQ16(plan.capUndulationSubvoxels,
+        std::int64_t cap=plan.capHeightSubvoxels+MulQ16(plan.capUndulationSubvoxels,
             Noise2D(x,y,plan.capWavelengthSubvoxels,recipe.seed,0x4341505f554e4431ull));
+        out.capHeightSubvoxels=cap;
         out.waterSurfaceSubvoxels=plan.waterSurfaceSubvoxels;
         return out;
     }
@@ -1816,6 +1817,65 @@ bool Heightfield2D::isValid() const noexcept
     });
 }
 
+std::array<std::int64_t,2> Heightfield2D::capHeightBounds() const noexcept
+{
+    if(!isValid())return {0,0};
+    long double Minimum=std::numeric_limits<long double>::infinity();
+    long double Maximum=-std::numeric_limits<long double>::infinity();
+    const auto IncludeBiome=[&](const WorldAssemblyBiomeProfileV1& Biome)
+    {
+        const long double Base=Biome.hasCapProfile
+            ?static_cast<long double>(Biome.capHeightSubvoxels)
+            :static_cast<long double>(plan_->capHeightSubvoxels);
+        const long double Undulation=Biome.hasCapProfile
+            ?static_cast<long double>(Biome.capUndulationSubvoxels)
+            :static_cast<long double>(plan_->capUndulationSubvoxels);
+        const long double Detail=Biome.hasCapProfile
+            ?static_cast<long double>(Biome.capDetailAmplitudeSubvoxels)
+            :static_cast<long double>(plan_->capDetailAmplitudeSubvoxels);
+        const long double Ridge=Biome.hasCapProfile
+            ?static_cast<long double>(Biome.capRidgeAmplitudeSubvoxels)
+            :static_cast<long double>(plan_->capRidgeAmplitudeSubvoxels);
+        Minimum=std::min(Minimum,Base-Undulation-Detail-Ridge);
+        Maximum=std::max(Maximum,Base+Undulation);
+    };
+    if(recipe_->biomes.empty())
+    {
+        const WorldAssemblyBiomeProfileV1 Fallback{};
+        IncludeBiome(Fallback);
+    }
+    else for(const auto& Biome:recipe_->biomes)IncludeBiome(Biome);
+    long double FeatureAmplitude=0.0L;
+    for(const auto& Feature:plan_->features)
+        if(Feature.type==3)
+            FeatureAmplitude+=std::abs(static_cast<long double>(Feature.parametersSubvoxels[0]));
+    Minimum-=FeatureAmplitude;Maximum+=FeatureAmplitude;
+    if(recipe_->evaluatorVersion>=5)
+    {
+        const long double TopSubvoxels=(static_cast<long double>(plan_->topChunkZ)+1.0L)
+            *CoreTileVoxelCount*WorldAssemblySubvoxelsPerVoxel;
+        Minimum=std::min(Minimum,TopSubvoxels);
+        Maximum=std::min(Maximum,TopSubvoxels);
+    }
+    const long double Int64Minimum=static_cast<long double>(std::numeric_limits<std::int64_t>::min());
+    const long double Int64Maximum=static_cast<long double>(std::numeric_limits<std::int64_t>::max());
+    return {static_cast<std::int64_t>(std::clamp(Minimum,Int64Minimum,Int64Maximum)),
+        static_cast<std::int64_t>(std::clamp(Maximum,Int64Minimum,Int64Maximum))};
+}
+
+std::int64_t Heightfield2D::farSurfaceCapHeightSubvoxels(std::int64_t x,
+    std::int64_t y) const noexcept
+{
+    if(!isValid())return 0;
+    const HeightfieldPointSample column=point(x,y,0);
+    if(recipe_->evaluatorVersion<5)return column.capHeightSubvoxels;
+    // Clip only the far render surface. Keep the near density evaluator bit-identical.
+    // Borner uniquement le plafond lointain. L'evaluateur de densite proche reste identique.
+    const std::int64_t ownedUpperBoundary=(static_cast<std::int64_t>(plan_->topChunkZ)+1)
+        *CoreTileVoxelCount*WorldAssemblySubvoxelsPerVoxel;
+    return std::min(column.capHeightSubvoxels,ownedUpperBoundary);
+}
+
 WorldAssemblyFeatureTileListV1 Heightfield2D::buildFeatureTileList(
     const std::array<std::int64_t,3>& minimum,
     const std::array<std::int64_t,3>& maximum) const