wip(L16, side branch): disk terrain cache design + headless Linux prototype

Exact lossless zlib tile records (keyed on world/season/recipe/plan/evaluator/options/tile),
pristine cache plus ordered edits, server never trusts client caches, corruption/stale rejection,
atomic writes, 2 GB cap. Loaded tiles match regenerated hashes (L1 view, 24 m crossing).
NOT for assembler/world yet: the shared StreamBenchmarkPipeline.h includes Linux-only headers
(unistd/fcntl/zlib), which would break the Windows viewer build.

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

Standalone/Source/StreamingWorld.h

@@ -67,6 +67,10 @@ struct FStandaloneCpuTile
 
 };
 
+using FStandaloneCoreTileRoute = std::function<std::optional<VoxelForgeCore::TileMesh>(
+    const VoxelForgeCore::World&,const VoxelForgeCore::TileKey&,
+    const VoxelForgeCore::TileGenerationOptions&,bool&,std::string&)>;
+
 inline uint64 HashStandaloneMeshPayload(const FVoxelMeshData& Mesh)
 {
     uint64 Hash=14695981039346656037ull;
@@ -430,14 +434,16 @@ public:
                                            VoxelForgeCore::World* InCoreWorld=nullptr,
                                            bool bInCaptureColumnCoordinates=false,
                                            int32 InLod8HorizonInteriorStepVoxels=0,
-                                           bool bInSharedColumnCache=true)
+                                           bool bInSharedColumnCache=true,
+                                           FStandaloneCoreTileRoute InCoreTileRoute={})
         :World(&InWorld),WorkerCount(FMath::Clamp(InWorkerCount,1,16)),bHashDensity(bInHashDensity),
          MeshCache(InMeshCache),MaxLevelFilter(InMaxLevelFilter),
          CoreWorld(InCoreWorld),bSkipUvAndColors(bInSkipUvAndColors),bSkipMaterialGroups(bInSkipMaterialGroups),
          bSkipUV(bInSkipUV),bSkipColors(bInSkipColors),
          bCaptureColumnCoordinates(bInCaptureColumnCoordinates),
          bSharedColumnCache(bInSharedColumnCache),
-         Lod8HorizonInteriorStepVoxels(std::max(0,InLod8HorizonInteriorStepVoxels))
+         Lod8HorizonInteriorStepVoxels(std::max(0,InLod8HorizonInteriorStepVoxels)),
+         CoreTileRoute(std::move(InCoreTileRoute))
     {
         VoxelGenLOD::InitializeConsoleSwitches();
         UVoxelMarchingCubesMesher::InitializeConsoleSwitches();
@@ -830,8 +836,11 @@ private:
             Options.diagnosticColumnInterpolationStride=
                 std::max<std::uint32_t>(1,DiagnosticCellStride);
             std::string Error;
-            auto Result=CoreWorld->generateTile(
-                {{Job.Key.Coord.X,Job.Key.Coord.Y,Job.Key.Coord.Z},Job.Key.Level},Options,Error);
+            const VoxelForgeCore::TileKey CoreKey{{Job.Key.Coord.X,Job.Key.Coord.Y,Job.Key.Coord.Z},Job.Key.Level};
+            bool bDiskCacheHit=false;
+            auto Result=CoreTileRoute
+                ?CoreTileRoute(*CoreWorld,CoreKey,Options,bDiskCacheHit,Error)
+                :CoreWorld->generateTile(CoreKey,Options,Error);
             if(!Result)
             {
                 std::fprintf(stderr,"[VoxelForgeCore] tile generation failed: %s\n",Error.c_str());
@@ -1003,6 +1012,7 @@ private:
     bool bCaptureColumnCoordinates=false;
     bool bSharedColumnCache=true;
     int32 Lod8HorizonInteriorStepVoxels=0;
+    FStandaloneCoreTileRoute CoreTileRoute;
     bool bProfileMesherStages=false;
     bool bAuditUniformBlockProofs=false;
     std::atomic<uint64> CacheHitCount{0};