fix(determinism): own sin/cos on the world path -- same world on every CPU, 3.5% faster

On Win64, FMath::Sin/Cos resolve to CRT sinf/cosf (GenericPlatformMath.h:521/530; no platform
override), and the UCRT picks FMA3 or non-FMA3 implementations at startup by CPU. /fp:precise
closed only the compiler half, so the same build and seed could build a slightly different world
on two Windows PCs, and on Linux.

- VoxelMath::DetSin/DetCos/DetSinCos (VoxelTypes.h): fixed double-precision period reduction to
  a quarter period, then fixed float minimax polynomials; no CRT, FMath or CPU-dependent
  intrinsic. Measured max error vs sinf 5.96e-8 over the used range (|arg| <= 6.19).
- Every world-deciding FMath::Sin/Cos replaced (generator, op stacks, cave morphology, strate
  manager, content placement, strate measure); none remain in runtime code.
- Pinned test VoxelForge.Determinism.DetSinCos (golden bit patterns + error bound).
- Diagnostic start-up switch -voxel.CrtFma3=0 (Windows) forces the CRT's non-FMA3 path.
- Parse-once console switches now initialise in StartupModule on the game thread; workers only
  read them (was an unsynchronised first parse inside GetDensityAt).
- Corrected the CRC comment that claimed a CRC32 cannot give a false positive.

Proof (Codex round; orchestrator re-checked):
- Before the fix, FMA3 on vs off was identical on this Ryzen 7 5800X3D: the hole exists but was
  not observed in this world. After the fix, the canonical exports are byte-identical with
  FMA3 on and off.
- The world changed once, as expected. New canonical export SHA-256 CBB8AE18...906F (geometry
  B9EF84AC; was B3E5F4C3...377); worms region 9242C093 (was 311CA42C), walk OBJ 20CCF7BD....
  Triangle counts unchanged in every tile. Order-independent nearest-vertex distance, worms
  region: max 8.7 micrometres (the reported "11.4 m" was a line-order artefact of a line-by-line
  OBJ diff); export region max 3e-5 m.
- Capability exact: player-fit 20,830, walk-reachable 10,909, connected. TilePostReachProof,
  sealed-proof, cross-platform and strate-crossing tests pass.
- Performance, headless game path, S/M/S/M vs the committed-tip DLL: static worker 27.41 s vs
  28.44 s (-3.6%), moving 59.59 s vs 61.74 s (-3.5%); LOD0 p50/p95 not worse.

From Sol's code review (DESIGN-SOL-2026-09-15-CODE.md, section 4.1), branch sol/deterministic-math.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TaFdXhTdYMkW1xrV6ApT6Y

Source/VoxelForge/Private/VoxelContentManager.cpp

@@ -501,9 +501,9 @@ void UVoxelContentManager::BuildCellSpawns(const UVoxelGenerator* Gen, const FTr
     for (int32 e = 0; e < Entries.Num(); ++e)
     {
         CosMaxSlope[e] = (Entries[e].Profile.MaxSlopeAngle < 89.99f)
-            ? FMath::Cos(FMath::DegreesToRadians(Entries[e].Profile.MaxSlopeAngle)) : -1.0f;
+            ? VoxelMath::DetCos(FMath::DegreesToRadians(Entries[e].Profile.MaxSlopeAngle)) : -1.0f;
         CosMinSlope[e] = (Entries[e].Profile.MinSlopeAngle > 0.01f)
-            ? FMath::Cos(FMath::DegreesToRadians(Entries[e].Profile.MinSlopeAngle)) : -1.0f;
+            ? VoxelMath::DetCos(FMath::DegreesToRadians(Entries[e].Profile.MinSlopeAngle)) : -1.0f;
     }
 
     // Per-COLUMN biome cache: ResolveBiomeSampleAt's noise-heavy cell classification is box-validated
@@ -647,8 +647,10 @@ void UVoxelContentManager::BuildCellSpawns(const UVoxelGenerator* Gen, const FTr
                     const float Ang    = VoxelHash::ToFloat01(IH) * 2.0f * PI;
                     const float RadVox = FMath::Lerp(Comp.RadiusMinVox, Comp.RadiusMaxVox,
                                                      VoxelHash::ToFloat01(VoxelHash::Mix(IH ^ 0x77u)));
-                    const float SatVX = VX + FMath::Cos(Ang) * RadVox;   // voxel, actor-local
-                    const float SatVY = VY + FMath::Sin(Ang) * RadVox;
+                    float SinAng = 0.0f, CosAng = 0.0f;
+                    VoxelMath::DetSinCos(SinAng, CosAng, Ang);
+                    const float SatVX = VX + CosAng * RadVox;   // voxel, actor-local
+                    const float SatVY = VY + SinAng * RadVox;
 
                     // Optional per-satellite gating (relief/moisture/biome-border at ITS own XY).
                     if (Comp.Profile.Conditions.Num() > 0 &&
@@ -693,8 +695,10 @@ void UVoxelContentManager::BuildCellSpawns(const UVoxelGenerator* Gen, const FTr
                             const float SAng    = VoxelHash::ToFloat01(JH) * 2.0f * PI;
                             const float SRadVox = FMath::Lerp(Sub.RadiusMinVox, Sub.RadiusMaxVox,
                                                               VoxelHash::ToFloat01(VoxelHash::Mix(JH ^ 0x77u)));
-                            const float SubVX = SatVX + FMath::Cos(SAng) * SRadVox;
-                            const float SubVY = SatVY + FMath::Sin(SAng) * SRadVox;
+                            float SinSAng = 0.0f, CosSAng = 0.0f;
+                            VoxelMath::DetSinCos(SinSAng, CosSAng, SAng);
+                            const float SubVX = SatVX + CosSAng * SRadVox;
+                            const float SubVY = SatVY + SinSAng * SRadVox;
 
                             if (Sub.Profile.Conditions.Num() > 0 &&
                                 !Gen->EvaluateTerrainConditions(Sub.Profile.Conditions, SubVX, SubVY, Ctx.BiomeCtx)) continue;
@@ -1230,9 +1234,9 @@ bool UVoxelContentManager::SpawnFromProfile(const FPlacementProfile& P, uint32 H
 
     // Surface-tilt gates (acos(|N.Z|); guarded so defaults cost no trig).
     if (P.MaxSlopeAngle < 89.99f &&
-        FMath::Abs(N.Z) < FMath::Cos(FMath::DegreesToRadians(P.MaxSlopeAngle))) return false;
+        FMath::Abs(N.Z) < VoxelMath::DetCos(FMath::DegreesToRadians(P.MaxSlopeAngle))) return false;
     if (P.MinSlopeAngle > 0.01f &&
-        FMath::Abs(N.Z) > FMath::Cos(FMath::DegreesToRadians(P.MinSlopeAngle))) return false;
+        FMath::Abs(N.Z) > VoxelMath::DetCos(FMath::DegreesToRadians(P.MinSlopeAngle))) return false;
 
     const FVector LocalPos(LocalX, LocalY, ZC * VOXEL_SIZE);
     if (P.bRequireWaterRelative && Ctx.bHasWater)