wip(assembler): round L4 -- lazy per-thread caches: 17.3 MiB -> 43 KiB per thread, view 7% faster

VoxelForgeCoreThreadLocal::FLazy<T> (new public header ThreadLocalStorage.h) makes every large
thread_local cache a pointer that heap-allocates on that thread's first use (still worker-private,
lock-free). Static TLS 17.33 MiB -> 43 KiB (initialised image 5.8 MiB -> 21 KiB); worker start
5.2 -> 0.12 ms; idle worker RSS 17.7 MiB -> 52 KiB. Linux workers back to 8 MiB stacks.
World unchanged (L1 hashes Clang off/GCC default, W1/W12; FloatingIslands seed 0).
Reviewer interleaved W12: 2.256 -> 2.091 s. MSVC/UBT not compiled here.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ED33VnqepD4YY6gDAAA832

CODEMAP.md

@@ -158,6 +158,7 @@ remains `0`, and lateral regions remain gated off.
 | `VoxelForge.Build.cs` | Deps: Core, CoreUObject, Engine, **GameplayTags**, **RealtimeMeshComponent**, `VoxelForgeCore`. `AVoxelWorld::bUseVoxelForgeCore` opts into the Core runtime route; it defaults off. |
 | `../../VoxelForgeCore/VoxelForgeCore.Build.cs` | C++20 runtime module. Reads `Standalone/Core/core_sources.txt`, validates one include shim per canonical source, and fails UBT on missing, extra, or mismatched shims. No unity/PCH; private copied implementation stays under `vfcore::detail`. |
 | `../../VoxelForgeCore/Private/Manifest/VFCore_*.cpp` | Eighteen one-source UBT shims that include canonical files under `Standalone/`; they do not copy Core implementation. The API-boundary row includes `Core/src/VoxelForgeCore.cpp` directly. |
+| `../../Standalone/Core/include/VoxelForgeCore/ThreadLocalStorage.h` | `VoxelForgeCoreThreadLocal::FLazy<T>`: thread-local handle that heap-allocates a worker-private cache on first use. All large Core and legacy caches use it (HeightfieldColumnCache, IslandColumnCache, GFloorReliefCache, GRoomGraphCache, GSurfColCache, tunnel/diff caches). See ARCHITECTURE §8.10. |
 | `../../Standalone/Core/src/CoreNamespacePreamble.h` | First include of every Core TU. Forces FP contraction off per compiler (Clang/MSVC/GCC pragmas; unknown compiler = `#error`) and defines `vfcore::fp_contract::selfTest`, which `World::compile` runs before building: a fused multiply-add (e.g. Clang `-ffp-contract=fast`) refuses world generation. The world depends on contraction (Linux2/Linux3 reports), so never remove either. |
 | `../../VoxelForgeCore/Private/ModuleEntry/` | Unreal module entry and an isolated `CoreMinimal.h` shim for the actual engine header. |
 | `../../Standalone/Core/include/VoxelForgeCore/VoxelForgeCore.h` | Standard-library-only public Core API. `VOXELFORGECORE_API` exports the API from the Unreal module and is empty for standalone builds. |