feat(D.2b): Slice 2 — DollEntityBuilder (player Setup+ObjDesc -> doll WorldEntity)

Mirrors the palette/part-override mapping at GameWindow.cs:3390-3431 in a
testable static helper. Build() accepts plain (SubPaletteId, Offset, Length)
and (PartIndex, GfxObjId) tuples, builds PaletteOverride only when
subPalettes.Count > 0 (same gate as GameWindow), and poses the entity at
origin facing the viewer (191.367905° / +Z). Reserved synthetic guid
0xDA11D011 keeps the doll distinct from the live player and satisfies
EntitySpawnAdapter's ServerGuid != 0 guard. 7 new tests green; suite 594/0.

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

tests/AcDream.App.Tests/Rendering/DollEntityBuilderTests.cs

@@ -0,0 +1,84 @@
+using System.Collections.Generic;
+using System.Numerics;
+using AcDream.App.Rendering;
+using AcDream.Core.World;
+using Xunit;
+
+namespace AcDream.App.Tests.Rendering;
+
+public class DollEntityBuilderTests
+{
+    [Fact]
+    public void Builds_doll_entity_with_synthetic_guid_and_player_setup()
+    {
+        // SubPaletteRange uses: SubPaletteId, Offset (byte), Length (byte)
+        var doll = DollEntityBuilder.Build(
+            setupId: 0x0200_0001u,
+            meshRefs: new List<MeshRef>(),
+            basePaletteId: 0x04000ABCu,
+            subPalettes: new (uint SubPaletteId, byte Offset, byte Length)[] { (0x0F00_0001u, 0, 8) },
+            partOverrides: new (byte PartIndex, uint GfxObjId)[] { (2, 0x0100_0042u) });
+
+        Assert.Equal(0x0200_0001u, doll.SourceGfxObjOrSetupId);
+        Assert.Equal(DollEntityBuilder.DollServerGuid, doll.ServerGuid);
+        Assert.NotEqual(0u, doll.ServerGuid);
+        Assert.Single(doll.PartOverrides);
+        Assert.Equal((byte)2, doll.PartOverrides[0].PartIndex);
+        Assert.Equal(0x0100_0042u, doll.PartOverrides[0].GfxObjId);
+        Assert.NotNull(doll.PaletteOverride);
+        Assert.Equal(0x04000ABCu, doll.PaletteOverride!.BasePaletteId);
+        Assert.Single(doll.PaletteOverride.SubPalettes);
+        Assert.Equal(0x0F00_0001u, doll.PaletteOverride.SubPalettes[0].SubPaletteId);
+    }
+
+    [Fact]
+    public void Null_overrides_give_empty_collections_not_null()
+    {
+        var doll = DollEntityBuilder.Build(0x0200_0001u, new List<MeshRef>(), null, null, null);
+        // No subpalettes => no PaletteOverride (mirrors GameWindow: only built when Count > 0)
+        Assert.Null(doll.PaletteOverride);
+        Assert.Empty(doll.PartOverrides);
+    }
+
+    [Fact]
+    public void Empty_subpalettes_give_null_palette_override()
+    {
+        // Mirror GameWindow: SubPalettes with Count == 0 => no override
+        var doll = DollEntityBuilder.Build(
+            0x0200_0001u,
+            new List<MeshRef>(),
+            basePaletteId: 0x04000001u,
+            subPalettes: System.Array.Empty<(uint, byte, byte)>(),
+            partOverrides: null);
+        Assert.Null(doll.PaletteOverride);
+    }
+
+    [Fact]
+    public void Heading_is_normalized_quaternion_facing_viewer()
+    {
+        var doll = DollEntityBuilder.Build(0x0200_0001u, new List<MeshRef>(), null, null, null);
+        Assert.True(System.MathF.Abs(doll.Rotation.LengthSquared() - 1f) < 1e-3f);
+    }
+
+    [Fact]
+    public void Position_is_world_origin()
+    {
+        var doll = DollEntityBuilder.Build(0x0200_0001u, new List<MeshRef>(), null, null, null);
+        Assert.Equal(Vector3.Zero, doll.Position);
+    }
+
+    [Fact]
+    public void ParentCellId_is_null_for_doll_scene()
+    {
+        var doll = DollEntityBuilder.Build(0x0200_0001u, new List<MeshRef>(), null, null, null);
+        Assert.Null(doll.ParentCellId);
+    }
+
+    [Fact]
+    public void MeshRefs_are_passed_through()
+    {
+        var refs = new List<MeshRef> { new MeshRef(0x01000001u, Matrix4x4.Identity) };
+        var doll = DollEntityBuilder.Build(0x0200_0001u, refs, null, null, null);
+        Assert.Same(refs, doll.MeshRefs);
+    }
+}