fix #203: preserve animation on appearance updates

src/AcDream.Core/World/WorldEntity.cs

@@ -4,6 +4,9 @@ namespace AcDream.Core.World;
 
 public sealed class WorldEntity
 {
+    private PaletteOverride? _paletteOverride;
+    private IReadOnlyList<PartOverride> _partOverrides = Array.Empty<PartOverride>();
+
     public required uint Id { get; init; }
     /// <summary>
     /// Server-assigned GUID (from CreateObject). Zero for dat-hydrated
@@ -34,7 +37,11 @@ public sealed class WorldEntity
     /// colors, creature recolors (e.g. stone-colored drudge statue),
     /// and team colors. Non-palette-indexed textures ignore this field.
     /// </summary>
-    public PaletteOverride? PaletteOverride { get; init; }
+    public PaletteOverride? PaletteOverride
+    {
+        get => _paletteOverride;
+        init => _paletteOverride = value;
+    }
 
     /// <summary>
     /// EnvCell or outdoor cell ID that owns this entity (room geometry, static
@@ -94,7 +101,30 @@ public sealed class WorldEntity
     /// <c>AnimatedEntityState</c>'s override map at spawn time. Empty for atlas-
     /// tier entities.
     /// </summary>
-    public IReadOnlyList<PartOverride> PartOverrides { get; init; } = Array.Empty<PartOverride>();
+    public IReadOnlyList<PartOverride> PartOverrides
+    {
+        get => _partOverrides;
+        init => _partOverrides = value;
+    }
+
+    /// <summary>
+    /// Replaces the render-only appearance carried by an ObjDesc update while
+    /// preserving this entity's identity, spatial state, and runtime owners.
+    /// Retail performs the equivalent mutation through
+    /// <c>CPhysicsObj::DoObjDescChangesFromDefault</c>.
+    /// </summary>
+    public void ApplyAppearance(
+        IReadOnlyList<MeshRef> meshRefs,
+        PaletteOverride? paletteOverride,
+        IReadOnlyList<PartOverride> partOverrides)
+    {
+        ArgumentNullException.ThrowIfNull(meshRefs);
+        ArgumentNullException.ThrowIfNull(partOverrides);
+
+        MeshRefs = meshRefs;
+        _paletteOverride = paletteOverride;
+        _partOverrides = partOverrides;
+    }
 
     /// <summary>
     /// Bitmask of hidden Setup parts. Bit <c>i</c> set hides part <c>i</c> at