# Research R2 — Unreal compile and behavior review

Read-only static review; no builds or tests run.

## Build baseline and Source history

The last recorded Windows BuildHost UBT pass is Round 18/S14, source commit `ec2afe9` (BuildHost UBT passed on its first attempt; the report lists `Source/VoxelForge/Private/VoxelWorld.cpp`). The older commit explicitly labelled “owner build” is `48fa028`; the newer BuildHost pass is the better compile baseline. No later UBT pass is recorded for these Source edits.

Since `ec2afe9`, the Unreal-side edits are:

- L11 `b1cfaf5`: `Private/VoxelWorld.cpp`
- L18 `dcf0763`: `Private/VoxelForgeCoreAdapter.cpp`, `Public/VoxelDensityPrimitives.h`
- L21 `8753f6d`: adapter
- L22 `55c26a0`: adapter, `Private/VoxelStrateManager.cpp`, `Public/VoxelSettings.h`, `Public/VoxelStrateManager.h`
- L23 `71d09a8`: adapter
- L24 `cb9236c`: adapter, `Public/VoxelStrateTypes.h`
- L25 `ef789aa`: adapter
- L27 `07b3fe2`: adapter
- L29 `63c7e56`: adapter, `Public/VoxelStrateTypes.h`
- L37 `3e443bf`: adapter

That is seven changed Source files: `VoxelForgeCoreAdapter.cpp`, `VoxelWorld.cpp`, `VoxelStrateManager.cpp`, `VoxelDensityPrimitives.h`, `VoxelSettings.h`, `VoxelStrateManager.h`, and `VoxelStrateTypes.h`.

## Findings

| File:line | Issue | Confidence | Suggested fix |
|---|---|---|---|
| `Source/VoxelForge/Private/VoxelForgeCoreAdapter.cpp:822` | Calls non-const `SetHardTransitionFallbackForAssembly` through `const UVoxelStrateManager*`; this is a C++ compile error and remains in the current worktree. | certain | Pass a mutable manager through the serializer/attach path, or perform the state change at a non-const caller. |
| `Standalone/Core/src/ShapeWorldInternal.h` (tracked HEAD line 1554) | Tracked HEAD has an extra `)` in its mouth-support `if`; the current L38 worktree replaces that passage-mouth block in a larger Core rewrite. | certain (HEAD only) | Preserve and review the current L38 diff before the owner builds. |
| `Source/VoxelForge/Private/VoxelStrateManager.cpp:1179` | New `std::llround` call has no direct `<cmath>` include; it may currently arrive transitively. | check | Add `<cmath>` to this translation unit. |
| `Source/VoxelForge/Private/VoxelWorld.cpp:13048` | New `unordered_set::contains` requires C++20; `VoxelForge.Build.cs` does not pin the standard. | check | Pin `CppStandard=Cpp20` here or use `find(...) != end()` if older language modes must work. |
| `Source/VoxelForge/Private/VoxelForgeCoreAdapter.cpp:137, 489, 543` | Route capsule dimensions are fixed in Core subvoxels; the Floating Islands recipe leaves `routeConstraints.version` zero, so Core fills 25 cm-sized defaults. At smaller Core voxel sizes, the proofs shrink in centimetres. | likely (when Core voxel size < 25 cm) | Set both route constraint sets from fixed gameplay dimensions in cm divided by `CoreVoxelSizeCm`. |
| `Source/VoxelForge/Private/VoxelWorld.cpp:7761` | Failed Core startup switches to legacy generation but does not clear the hard-transition flag set by the adapter at line 822; legacy parameter lookups then keep the Core-only hard fallback. | likely | Clear the flag in `FallBackToLegacyAfterCoreInitializationFailure`. |

No likely UHT blocker found in the changed headers: the new reflected setting is a `float` with numeric clamp metadata; the Blueprint enums remain `: uint8`; changed reflected declarations add no `uint64`/`int64` properties. UE documents `uint32`/`int64` as property integer types and metres as a supported unit. [UE Properties](https://dev.epicgames.com/documentation/unreal-engine/unreal-engine-uproperties?lang=en-US) · [UE Units](https://dev.epicgames.com/documentation/unreal-engine/units-of-measurement-in-unreal-engine?lang=en-US). `VoxelDensityPrimitives.h` adds inline shared helpers; the other header changes are layout state, comments, or the intentional Worm default. No designated initializers, `__restrict`, or suspicious new narrowing were found.

Core’s module pins C++20 and precise FP semantics. `CoreNamespacePreamble.h` selects a compiler-specific contraction control; the MSVC branch uses `#pragma fp_contract(off)`, and `World::compile` rejects a build if its FMA self-test fails. MS documents that pragma from VS2022 17.0 and that older compilers could contract under `/fp:precise`; confirm the owner’s toolset and check the startup self-test. [UE C++ standard](https://dev.epicgames.com/documentation/unreal-engine/epic-cplusplus-coding-standard-for-unreal-engine) · [MSVC `/fp`](https://learn.microsoft.com/en-us/cpp/build/reference/fp-specify-floating-point-behavior?view=msvc-170) · [MSVC `fp_contract`](https://learn.microsoft.com/en-us/cpp/preprocessor/fp-contract). Core unordered containers appear to serve lookup, membership, statistics, or lookup-table construction; I found no output-affecting hash iteration.

At final review, L38 had an uncommitted worktree diff across six files (136 insertions / 1,002 deletions), including removal of `terrainFollowingRoute` from the Core recipe and both plan producers; no live code references remain. This is a substantial in-progress evaluator change with no UBT confirmation. No other stale Core/adapter recipe-field mismatch was found in the current worktree.

## Behavior risks

- SurfaceWorld and FloatingIslands intentionally use different historical voxel conventions: SurfaceWorld layout chunks are 32 Core voxels (8 m at 25 cm); FloatingIslands converts 32 owner voxels (12.5 cm) through the owner/Core ratio (4 m at 25 cm). The L20/L22 research records this split. Do not blanket-apply the FI scale to SurfaceWorld; compare physical anchors and route clearances if using a non-25 cm Core size.
- Route proofs assume a 34 cm radius, 176 cm tall player capsule at 25 cm Core voxels. At 12.5 cm, the fixed Q values represent half those physical dimensions; the FI Core fallback also silently supplies fixed defaults because the adapter never sets `routeConstraints`.
- On adapter validation/export failure, the hard-transition flag set at adapter line 822 can leak into the legacy fallback path. This can make the fallback world differ from the normal legacy generator.
- FP behavior is fail-closed rather than silently divergent on unsupported MSVC: if contraction is detected, Core initialization refuses to generate. Linux1’s Clang/GCC checks do not validate the owner’s MSVC binary.

## What the owner should check first when he builds

1. Build the current worktree (including the current L38 Core rewrite); expect the adapter constness error first unless the implementation fixes it.
2. Check UHT, then confirm the owner project’s language mode accepts `unordered_set::contains`; add the direct `<cmath>` include if MSVC reports `llround` unresolved.
3. Confirm Core startup passes the FP self-test. Then validate one SurfaceWorld and one FloatingIslands route at the configured Core voxel size, especially if it is below 25 cm; inspect startup plan errors and the route capsule/support clearance.

## Orchestrator follow-up (Claude)

Both "certain" findings were confirmed and fixed in the same commit:
- **`ShapeWorldInternal.h:1554` stray `)`** — L37's committed Core did not compile. It was left when a temporary
  support-off diagnostic was restored after the final build. Fixed; a clang build of the fixed HEAD reproduces L37's
  verified owner-world hashes exactly (SurfaceWorld and FloatingIslands, L25 W12).
- **Adapter constness (`VoxelForgeCoreAdapter.cpp:823`)** — the setter is now `const` over a `mutable` runtime flag.
- Also applied: the legacy fallback clears that flag, and `<cmath>` is included in `VoxelStrateManager.cpp`.
- Left for the owner's build: `unordered_set::contains` (UE5 modules default to C++20), and the FI route-constraint
  scaling at Core voxel sizes other than 25 cm (only matters if he changes it).