test(lighting): lock the bake contract on golden torches (A7 Fix D oracle)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/AcDream.Core.Tests/Lighting/LightBakeConformanceTests.cs

@@ -0,0 +1,78 @@
+using System.Collections.Generic;
+using System.Numerics;
+using AcDream.Core.Lighting;
+using Xunit;
+
+namespace AcDream.Core.Tests.Lighting;
+
+/// <summary>
+/// Golden conformance for the retail bake (calc_point_light + the [0,1] clamp),
+/// driven by the live-cdb-captured Holtburg wall torches. Pins the contract that
+/// mesh_modern.vert's pointContribution + the new pointAcc clamp (A7 Fix D, D-1)
+/// must mirror line-for-line. See docs/research/2026-06-18-lighting-a7-fixABC-shipped-fixD-handoff.md.
+/// </summary>
+public class LightBakeConformanceTests
+{
+    private static LightSource OrangeTorch(Vector3 pos) => new()
+    {
+        Kind = LightKind.Point,
+        WorldPosition = pos,
+        ColorLinear = new Vector3(1.0f, 0.588f, 0.314f), // captured orange
+        Intensity = 100f,
+        Range = 4f * 1.3f,                               // falloff 4 × static_light_factor
+        IsLit = true,
+    };
+
+    [Theory]
+    [InlineData(1f)]
+    [InlineData(2f)]
+    [InlineData(3f)]
+    [InlineData(4f)]
+    [InlineData(5f)]
+    public void SingleOrangeTorch_IsWarmAndBounded_NeverWhite(float dist)
+    {
+        var vtx = Vector3.Zero;
+        var normal = Vector3.UnitX;
+        var torch = OrangeTorch(new Vector3(dist, 0f, 0f));
+
+        var c = LightBake.ComputeVertexColor(vtx, normal, new[] { torch });
+
+        Assert.InRange(c.X, 0f, 1f);
+        Assert.InRange(c.Y, 0f, 1f);
+        Assert.InRange(c.Z, 0f, 1f);
+        if (c.X > 0f)
+        {
+            Assert.True(c.X >= c.Y, $"R({c.X}) >= G({c.Y}) at d={dist}");
+            Assert.True(c.Y >= c.Z, $"G({c.Y}) >= B({c.Z}) at d={dist}");
+        }
+    }
+
+    [Fact]
+    public void BeyondRange_ContributesNothing()
+    {
+        var torch = OrangeTorch(new Vector3(100f, 0f, 0f));
+        var c = LightBake.ComputeVertexColor(Vector3.Zero, Vector3.UnitX, new[] { torch });
+        Assert.Equal(Vector3.Zero, c);
+    }
+
+    [Fact]
+    public void ManyOverlappingIntenseTorches_StillClampToOne()
+    {
+        var lights = new List<LightSource>();
+        for (int i = 0; i < 8; i++)
+            lights.Add(new LightSource
+            {
+                Kind = LightKind.Point,
+                WorldPosition = new Vector3(1.5f, 0.1f * i, 0f),
+                ColorLinear = new Vector3(0.98f, 0.95f, 0.9f),
+                Intensity = 100f,
+                Range = 5.2f,
+                IsLit = true,
+            });
+
+        var c = LightBake.ComputeVertexColor(Vector3.Zero, Vector3.UnitX, lights);
+        Assert.InRange(c.X, 0f, 1f);
+        Assert.InRange(c.Y, 0f, 1f);
+        Assert.InRange(c.Z, 0f, 1f);
+    }
+}