wip(assembler): round L3 -- Core forces FP contraction off and refuses to generate if it can't

CoreNamespacePreamble.h applies per-compiler contraction-off pragmas (Clang, MSVC, GCC; unknown
compiler = #error) and a fused-multiply-add self-test that World::compile runs before building.
Clang -ffp-contract=on and GCC's default (fast) now reproduce the L1/Windows hashes (they diverged
in L2); Clang -ffp-contract=fast ignores the pragma and is refused at startup (negative control).
Seed sweep with every cube on real terrain: 48 seeds x 2 recipes x 3 builds x W1/W12, 576 runs,
0 mismatches, 0 empty meshes. Cost +0.5% (2.326 -> 2.337 s, interleaved). World unchanged.
MSVC/UBT not compiled here: Windows to-do list in Linux3/REPORT.md.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Standalone/Source/StreamBenchmarkPipeline.h

@@ -62,7 +62,7 @@ namespace StandaloneStreamBenchmark
         VoxelForgeCore::DetailVariant DetailVariant,const VoxelForgeCore::JobScheduler& Scheduler,
         bool bHashDensity,bool bSkipUvAndColors,bool bSkipMaterialGroups,bool bSkipUV,bool bSkipColors,
         std::chrono::steady_clock::time_point ColdStart,bool bProfileColumnOverlap,
-        int32 FarHorizonLOD8InteriorStepVoxels)
+        int32 FarHorizonLOD8InteriorStepVoxels,bool bReportMeshCoverage=false)
     {
         using Clock=std::chrono::steady_clock;
         FStandaloneOwnerWorld& World=*OwnerWorld;
@@ -166,6 +166,7 @@ namespace StandaloneStreamBenchmark
         std::vector<FHashedTile> DensityRows,MeshRows,PayloadRows,TopologyRows;
         int32 Finished=0,NeighborhoodFinished=0,FullDetailFinished=0;
         int32 FullDetailExpected=0;
+        uint64 WholeNonEmptyMeshTiles=0,WholeTriangleCount=0;
         struct FColumnXY
         {
             std::int64_t X=0,Y=0;
@@ -222,6 +223,12 @@ namespace StandaloneStreamBenchmark
             for(const FStandaloneCpuTile& Tile:Ready)
             {
                 ++Finished;
+                if(bReportMeshCoverage)
+                {
+                    const uint64 TileTriangleCount=static_cast<uint64>(Tile.Indices.size()/3);
+                    WholeTriangleCount+=TileTriangleCount;
+                    if(TileTriangleCount>0)++WholeNonEmptyMeshTiles;
+                }
                 if(Tile.Key.Level>=0&&Tile.Key.Level<static_cast<int32>(TileCountByLOD.size()))
                 {
                     const std::size_t LOD=static_cast<std::size_t>(Tile.Key.Level);
@@ -348,6 +355,10 @@ namespace StandaloneStreamBenchmark
             WorkerCount,ShapeSeconds,NeighborhoodMeshSeconds,NeighborhoodSeconds,
             FullDetailSeconds,WholeViewSeconds,NeighborhoodFinished,
             FullDetailFinished,FullDetailExpected,Finished,Desired.Tiles.size(),StreamSeconds);
+        if(bReportMeshCoverage)
+            std::printf("[PipelineMeshCoverage] tiles=%d nonempty_mesh_tiles=%llu indexed_triangles=%llu\n",
+                Finished,static_cast<unsigned long long>(WholeNonEmptyMeshTiles),
+                static_cast<unsigned long long>(WholeTriangleCount));
         std::printf("[WorldAssemblerTilePipeline] full_detail_tiles=%d solid_boxes=%llu air_boxes=%llu mixed_boxes=%llu unknown_boxes=%llu whole_tile_skips=%llu field_calls=%llu column_cache_hits=%llu column_cache_misses=%llu column_compute_worker_ms=%.3f classification_worker_ms=%.3f meshing_worker_ms=%.3f\n",
             FullDetailExpected,static_cast<unsigned long long>(NativeSolidBoxes),
             static_cast<unsigned long long>(NativeAirBoxes),