experiment: LivingPlane repeatable + standalone UE runtime module (L164)

Readback barrier fix (GL_TEXTURE_UPDATE_BARRIER_BIT before glGetTexImage); check_repeatability.py compares full-field
checksums across query/capture settings - Intel GPU PASS (3b9d45905c7aafff), llvmpipe PASS, mismatch control fails.
New runtime module VoxelForgeLivingPlane (separate from generation): RDG global shader (Shaders/LivingPlane.usf),
ping-pong RGBA32F render targets, actor with WPO plane and object inputs, no CPU readback. Compiles in Linux UE 5.7.
Windows build: Source/VoxelForgeLivingPlane/*, Shaders/LivingPlane.usf, VoxelForge.uplugin. Setup: UE-SETUP.md.

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

Shaders/LivingPlane.usf

@@ -0,0 +1,85 @@
+Texture2D<float4> SourceState;
+RWTexture2D<float4> TargetState;
+
+int2 GridSize;
+float Dt;
+float Dx;
+float PlaneLength;
+float WaveSpeed;
+float Damping;
+float FoundationStiffness;
+float TimeSeconds;
+float2 BreathingSettings;
+float4 ImprintSettings;
+float4 ObjectPositionRadius[2];
+float4 ObjectVelocityPush[2];
+
+[numthreads(8, 8, 1)]
+void MainCS(uint3 DispatchThreadId : SV_DispatchThreadID)
+{
+	int2 Pixel = int2(DispatchThreadId.xy);
+	if (Pixel.x >= GridSize.x || Pixel.y >= GridSize.y)
+	{
+		return;
+	}
+
+	int2 Lo = int2(0, 0);
+	int2 Hi = GridSize - 1;
+	float4 State = SourceState.Load(int3(Pixel, 0));
+	float Height = State.r;
+	float Velocity = State.g;
+	float Imprint = State.b;
+	float Left = SourceState.Load(int3(max(Pixel + int2(-1, 0), Lo), 0)).r;
+	float Right = SourceState.Load(int3(min(Pixel + int2(1, 0), Hi), 0)).r;
+	float Down = SourceState.Load(int3(max(Pixel + int2(0, -1), Lo), 0)).r;
+	float Up = SourceState.Load(int3(min(Pixel + int2(0, 1), Hi), 0)).r;
+	float Laplacian = (Left + Right + Down + Up - 4.0 * Height) / max(Dx * Dx, 1.0e-8);
+	float2 World = (float2(Pixel) + 0.5) * Dx - PlaneLength * 0.5;
+
+	float Interaction = 0.0;
+	float Contact = 0.0;
+	for (int ObjectIndex = 0; ObjectIndex < 2; ++ObjectIndex)
+	{
+		float4 PositionRadius = ObjectPositionRadius[ObjectIndex];
+		if (PositionRadius.w <= 0.0)
+		{
+			continue;
+		}
+
+		float4 VelocityPush = ObjectVelocityPush[ObjectIndex];
+		float Radius = PositionRadius.w;
+		float Sigma = max(Radius * (0.58 / 0.43), Dx);
+		float2 Offset = World - PositionRadius.xy;
+		float Weight = exp(-dot(Offset, Offset) / max(2.0 * Sigma * Sigma, 1.0e-8));
+		float HeightAboveContact = max(PositionRadius.z - Radius, 0.0);
+		float ContactHeight = 1.0 - smoothstep(0.0, max(Radius, Dx), HeightAboveContact);
+		float ImpactSpeed = length(VelocityPush.xy) * 0.25 + max(-VelocityPush.z, 0.0) * 0.5;
+		float Push = max(VelocityPush.w, 0.0) + ImpactSpeed;
+		Interaction -= Push * Weight * ContactHeight;
+		if (Push > 0.0)
+		{
+			Contact = max(Contact, Weight * ContactHeight);
+		}
+	}
+
+	float Breathing = 0.0;
+	if (BreathingSettings.x != 0.0)
+	{
+		float Swell = sin(World.x * 0.48 - TimeSeconds * 0.22)
+			* cos(World.y * 0.42 + TimeSeconds * 0.16);
+		Breathing = BreathingSettings.y * Swell * sin(TimeSeconds * 0.48);
+	}
+
+	float NextImprint = Imprint;
+	if (ImprintSettings.x != 0.0)
+	{
+		NextImprint = clamp(Imprint * exp(-Dt / max(ImprintSettings.z, 1.0e-4))
+			- Contact * ImprintSettings.y * Dt, -ImprintSettings.w, 0.0);
+	}
+	float FoundationTarget = ImprintSettings.x != 0.0 ? Imprint : 0.0;
+	float Acceleration = WaveSpeed * WaveSpeed * Laplacian
+		- FoundationStiffness * (Height - FoundationTarget) + Interaction + Breathing;
+	float NextVelocity = (Velocity + Acceleration * Dt) * exp(-Damping * Dt);
+	float NextHeight = Height + NextVelocity * Dt;
+	TargetState[Pixel] = float4(NextHeight, NextVelocity, NextImprint, 0.0);
+}