wip(L17, side branch): FloatingIslands seal-cap fix + owner/Core chunk-scale change (breaks SurfaceWorld)

Not for assembler/world: the 8 m -> 4 m strate chunk change moves every stratum, so the SurfaceWorld
spawn camera floats in a void and the L1 mesh export shrank 58.7 -> 31.7 MB. Kept for its
diagnostics, the boundarySeal finding and the readable capture shading. See Linux17/REPORT.md.

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

Standalone/Source/StreamBenchmarkHeadless.cpp

@@ -63,6 +63,7 @@ namespace
         float CameraYawDegrees=0.0f;
         float CameraPitchDegrees=0.0f;
         std::filesystem::path MeshExportPath;
+        std::filesystem::path WorldAssemblyManifestOutputPath;
     };
 
     bool ParseInteger(std::string_view text,int& output)
@@ -115,6 +116,7 @@ namespace
                     "  --region-crossing (compile entering Core regions at the camera step)\n"
                     "  --column-cache=shared|thread-local (default: shared)\n"
                     "  --mesh-export=FILE (write the exact generated tile meshes for offline rendering)\n"
+                    "  --world-assembler-manifest-output=FILE (write the resolved plan for diagnostics)\n"
                     "  --profile-column-overlap --far-horizon-lod8-step=N --force-generate\n"
                     "  --seed=N --recipe=surface-world|floating-islands\n"
                     "  --auto-surface-camera (place the 27-tile cube on this seed's surface)\n"
@@ -204,6 +206,13 @@ namespace
                 if(options.MeshExportPath.empty())
                 {std::fprintf(stderr,"--mesh-export needs a file path\n");return false;}
             }
+            else if(arg.starts_with("--world-assembler-manifest-output="))
+            {
+                options.WorldAssemblyManifestOutputPath=std::filesystem::path(
+                    arg.substr(std::string_view("--world-assembler-manifest-output=").size()));
+                if(options.WorldAssemblyManifestOutputPath.empty())
+                {std::fprintf(stderr,"--world-assembler-manifest-output needs a file path\n");return false;}
+            }
             else if(arg.starts_with("--workers="))
             {if(!readInt("--workers=",options.WorkerCount))return false;}
             else if(arg.starts_with("--clip-radius="))
@@ -314,6 +323,22 @@ int main(int argc,char** argv)
         &&!StandaloneWorldAssemblyPrototype::AttachFloatingIslandWorldAssembly(
             *ownerWorld,ownerJsonRoot,worldAssembly,error))
     {std::fprintf(stderr,"Floating-island assembly setup failed: %s\n",error.c_str());return 2;}
+    if(!options.WorldAssemblyManifestOutputPath.empty())
+    {
+        std::error_code directoryError;
+        const auto parent=options.WorldAssemblyManifestOutputPath.parent_path();
+        if(!parent.empty())std::filesystem::create_directories(parent,directoryError);
+        if(directoryError)
+        {std::fprintf(stderr,"Manifest output directory failed: %s\n",directoryError.message().c_str());return 2;}
+        std::ofstream manifestFile(options.WorldAssemblyManifestOutputPath,std::ios::binary|std::ios::trunc);
+        if(!manifestFile)
+        {std::fprintf(stderr,"Cannot write manifest output: %s\n",options.WorldAssemblyManifestOutputPath.string().c_str());return 2;}
+        manifestFile<<worldAssembly.ToJson()<<'\n';
+        if(!manifestFile)
+        {std::fprintf(stderr,"Manifest output write failed: %s\n",options.WorldAssemblyManifestOutputPath.string().c_str());return 2;}
+        std::printf("[WorldAssemblyManifest] path=%s status=PASS\n",
+            options.WorldAssemblyManifestOutputPath.string().c_str());
+    }
     if(options.AutoSurfaceCamera)
     {
         constexpr std::int64_t UnitsPerVoxel=VoxelForgeCore::WorldAssemblySubvoxelsPerVoxel;