fix(core): smooth tunnel entrance floor; verifier keeps baselines out of /tmp (L47); research R14

The demo tunnel's hard floor cap used a vertical Z - floorZ on a sloped Bezier floor, which is not a signed
distance, so marching cubes produced a staircase through the first 7 m (40-51 mm ripple, 82 mm steps). The
cap now uses the grade-normalised signed distance with a floor-adjacent bore re-application fading over the
entrance; mesh tile Z bounds include cavern bounds. New three-rail entrance audit: L46 fails, L47 passes.
verify: the cost baseline exports only build inputs into Saved/Linux/<out>/baseline-<commit> and removes it;
/tmp unchanged after a full tier. Demo off: owner hashes identical to L46. fast/medium/full PASS.
Known: sawtooth at the tunnel wall foot (next round). Research R14: Windows/MSVC readiness review.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016dhxM43dnWvUu2B5Ph1iG1

Standalone/Research/WorldAssemblerM3/Research14/REPORT.md

@@ -0,0 +1,31 @@
+# VoxelForge R14 — Windows build review
+
+**Verdict:** I found no likely MSVC or UHT compile blocker in the requested diff. This is a source review, not a build result. Runtime behavior has one important condition: the legacy chunk callers align with the new physical layout only at the default 8 m width.
+
+## Compile and UHT review
+
+The diff adds no designated initializers, `__int128`, GNU builtins, `[[likely]]`, or `std::visit` use. The `std::variant` code has `<variant>` available; Core uses C++20, and the `std::llround` calls have `<cmath>` available. The new `FStrateSlot` metadata is plain non-`UPROPERTY` data.
+
+| File:line | Issue | Surety | One-line fix |
+|---|---|---|---|
+| [CoreNamespacePreamble.h:60](/home/jahni/VoxelM/Plugins/VoxelForge/Standalone/Core/src/CoreNamespacePreamble.h:60), [VoxelForgeCore.Build.cs:41](/home/jahni/VoxelM/Plugins/VoxelForge/Source/VoxelForgeCore/VoxelForgeCore.Build.cs:41) | Toolchain check: the Core build uses C++20 and MSVC’s `fp_contract` pragma. Core pins C++20 and precise FP; confirm the owner’s UBT-selected MSVC version and flags. | check | Use the UE-supported VS2022 toolset and confirm `/std:c++20` and `/fp:precise` in the build log. |
+
+Epic documents C++20 as UE’s default and minimum, and UBT’s module settings come from `.Build.cs` files ([C++ standard](https://dev.epicgames.com/documentation/unreal-engine/epic-cplusplus-coding-standard-for-unreal-engine), [module properties](https://dev.epicgames.com/documentation/unreal-engine/module-properties-in-unreal-engine)). Microsoft documents that `/fp:precise` disables contraction by default starting with Visual Studio 2022; earlier versions could contract, while the Core preamble explicitly requests `fp_contract(off)` ([`/fp`](https://learn.microsoft.com/en-us/cpp/build/reference/fp-specify-floating-point-behavior?view=msvc-170), [`fp_contract`](https://learn.microsoft.com/en-us/cpp/preprocessor/fp-contract?view=msvc-160)).
+
+## Behaviour risks
+
+- **Chunk coordinates versus micrometre bounds:** [VoxelStrateManager.cpp:1201](/home/jahni/VoxelM/Plugins/VoxelForge/Source/VoxelForge/Private/VoxelStrateManager.cpp:1201) resolves physical layout width in micrometres, but [GetStrateForChunk/GetStrateChunkZBounds](/home/jahni/VoxelM/Plugins/VoxelForge/Source/VoxelForge/Private/VoxelStrateManager.cpp:6298) and [IsGapChunk](/home/jahni/VoxelM/Plugins/VoxelForge/Source/VoxelForge/Private/VoxelStrateManager.cpp:6398) still treat `ChunkCoord.Z` as a layout-chunk index. Normal world chunk coordinates use `CHUNK_SIZE` voxels ([VoxelTypes.h:285](/home/jahni/VoxelM/Plugins/VoxelForge/Source/VoxelForge/Public/VoxelTypes.h:285)). Those units match at the default 8 m width with 25 cm voxels; the setting also allows 0.25–64 m. At other widths, generator selection, gap detection, and transition distances can disagree with the physical slot bounds. Enforce the matching width or convert these chunk APIs using the actual streaming-chunk width.
+
+- **Stamp and cavern graph records:** The Unreal adapter builds strata and passages, then finalizes its layout JSON ([VoxelForgeCoreAdapter.cpp:1078](/home/jahni/VoxelM/Plugins/VoxelForge/Source/VoxelForge/Private/VoxelForgeCoreAdapter.cpp:1078), [1260](/home/jahni/VoxelM/Plugins/VoxelForge/Source/VoxelForge/Private/VoxelForgeCoreAdapter.cpp:1260)); it does not call either stamp or graph resolver. The Core world is active in Unreal, but the adapter currently supplies it with no L43–L46 stamp or graph records. The current headless demo calls those resolvers directly ([StreamBenchmarkHeadless.cpp:933](/home/jahni/VoxelM/Plugins/VoxelForge/Standalone/Source/StreamBenchmarkHeadless.cpp:933)). To get that geometry in Unreal, the adapter needs to build and serialize those records.
+
+- **Bezier FP contraction:** The new Newton solve is in [ShapeWorldInternal.h:6090](/home/jahni/VoxelM/Plugins/VoxelForge/Standalone/Core/src/ShapeWorldInternal.h:6090). Core’s compile preamble disables contraction for MSVC, and `World::compile` runs a contraction self-check before compiling the shape. The solve itself has no graph input from the current Unreal adapter, so it should not execute in the current plugin path. Confirm the owner’s MSVC toolset; Microsoft documents version-dependent `/fp:precise` defaults as above.
+
+## First-build checklist
+
+1. Confirm the UE minor version and UBT-selected VS2022/MSVC toolset.
+2. Build the Win64 Development Editor target through UBT so it runs UHT and compiles both plugin modules; UBT takes module settings from `.Build.cs`.
+3. Check the first UHT or MSVC diagnostic, then confirm the Core compile flags include C++20 and precise FP.
+4. Launch the editor with the default 8 m layout and confirm Core world initialization succeeds, including its FP self-check.
+5. If using a non-default layout width, resolve the chunk-coordinate mismatch before relying on streamed generator and gap behavior. Do not expect the stamp/graph demo geometry in Unreal until the adapter supplies those records.
+
+I left the tree untouched. `git status` showed `Standalone/Research/WorldAssemblerM3/Linux18/exports/` as pre-existing untracked content.