standalone: the owner's world outside Unreal -- bit-identical density, D3D11 fly-through viewer

Standalone/ (C++20, MSVC /O2 /arch:AVX2 /fp:precise, Build.ps1): copied density pipeline, op stack,
cave morphology, passages, strate manager/composer, noise, DetSinCos, mesher, clipmap selection,
with a UE compatibility layer (Compat/). Owner data exported once to Standalone/data/owner_world.json
by a default-off explore-commandlet exporter (the only plugin-source change). 25 cm voxels.
Parity: seed 0, 3,436 samples (strate edges, negative/far coords, rooms, tunnels, passages,
landings): bit-identical. Viewer: full 7-level clipmap, per-level toggles 1-7, T = round winding
tunnels (standalone option), N/P seed, F wireframe.
Timing NOT yet a baseline: 515 s for 12,054 tiles (L0 70 s, L6 296 s); the compat TMap/TSet are
vector-backed with linear lookup, which the plugin's caches do not expect.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MmSoF64BbRFmk9C3p1VsBJ

Standalone/Source/VoxelForge/Private/VoxelStrateDefinition.cpp

@@ -0,0 +1,79 @@
+// Serialized strate-definition migrations.
+
+#include "VoxelStrateDefinition.h"
+
+#include "Serialization/CustomVersion.h"
+#include "VoxelPassageGeometry.h"
+
+namespace
+{
+    // The field name is retained for package compatibility, but version 1 changes its meaning
+    // from a raw tangent/gradient to authored degrees. This GUID is local to the plugin.
+    const FGuid GVoxelForgeStrateSerializationVersion(
+        0xA76D5E31, 0x4B2C4F9A, 0xB8C1D204, 0x6E9F7738);
+    constexpr int32 GVoxelForgeStrateGentleSlopeDegreesVersion = 1;
+    FCustomVersionRegistration GVoxelForgeStrateSerializationRegistration(
+        GVoxelForgeStrateSerializationVersion,
+        GVoxelForgeStrateGentleSlopeDegreesVersion,
+        TEXT("VoxelForgeStrateSerialization"));
+
+    float LegacyGradientToDegrees(float LegacyGradient)
+    {
+        if (!VoxelMath::IsFinite(LegacyGradient) || LegacyGradient <= 0.0f)
+        {
+            return 0.0f;
+        }
+        if (LegacyGradient >= 4096.0f)
+        {
+            return VoxelPassageGeometry::TunnelFloorGentleSlopeMaximumDegrees;
+        }
+
+        // Invert the old gradient without atan/tan. The same deterministic sine/cosine helper
+        // used by generation makes this migration independent of the host CRT.
+        float LowDegrees = 0.0f;
+        float HighDegrees = VoxelPassageGeometry::TunnelFloorGentleSlopeMaximumDegrees;
+        for (int32 Iteration = 0; Iteration < 32; ++Iteration)
+        {
+            const float MidDegrees = (LowDegrees + HighDegrees) * 0.5f;
+            float SinValue = 0.0f;
+            float CosValue = 0.0f;
+            VoxelMath::DetSinCos(
+                SinValue, CosValue, MidDegrees * (PI / 180.0f));
+            const float MidGradient = FMath::Min(
+                FMath::Abs(SinValue) / FMath::Max(FMath::Abs(CosValue), 1.0e-3f),
+                4096.0f);
+            if (MidGradient < LegacyGradient)
+            {
+                LowDegrees = MidDegrees;
+            }
+            else
+            {
+                HighDegrees = MidDegrees;
+            }
+        }
+        return FMath::Clamp(
+            (LowDegrees + HighDegrees) * 0.5f,
+            0.0f,
+            VoxelPassageGeometry::TunnelFloorGentleSlopeMaximumDegrees);
+    }
+}
+
+void UVoxelStrateDefinition::PostLoad()
+{
+    Super::PostLoad();
+
+    // The field remains reflected solely so old packages deserialize without shifting the
+    // following members.  Tunnel geometry owns the floor now, so every serialized legacy value
+    // is normalized to the ignored compatibility default before any runtime copy is made.
+    GenerationParams.bTunnelFloorEnabled = true;
+
+    if (GetLinkerCustomVersion(GVoxelForgeStrateSerializationVersion)
+        >= GVoxelForgeStrateGentleSlopeDegreesVersion)
+    {
+        return;
+    }
+
+    const float LegacyGradient = GenerationParams.TunnelFloorGentleSlopeThreshold;
+    GenerationParams.TunnelFloorGentleSlopeThreshold =
+        LegacyGradientToDegrees(LegacyGradient);
+}