fix: workaround VRCSDK bug where stale data is left in physbone state

Closes: bdunderscore/modular-avatar#845

Editor/VRChat/ForceReinitPhysBonesHook.cs

@@ -0,0 +1,35 @@
+#region
+
+using UnityEngine;
+using VRC.SDK3.Dynamics.PhysBone.Components;
+using VRC.SDKBase.Editor.BuildPipeline;
+
+#endregion
+
+namespace nadena.dev.ndmf.VRChat
+{
+    /// <summary>
+    /// When domain reload is disabled, the VRChat physbones gizmo can leave outdated data in the VRCPhysBone component
+    /// when entering play mode. Force reinitialize the components to work around this issue.
+    ///
+    /// Note that we only do this when entering play mode, as this is runtime state, not serialized state.
+    /// </summary>
+    public class ForceReinitPhysBonesHook : IVRCSDKPreprocessAvatarCallback
+    {
+        public int callbackOrder => int.MaxValue;
+
+        public bool OnPreprocessAvatar(GameObject avatarGameObject)
+        {
+            if (Application.isPlaying)
+            {
+                foreach (var physBone in avatarGameObject.GetComponentsInChildren<VRCPhysBone>(true))
+                {
+                    physBone.InitTransforms(true);
+                    physBone.InitParameters();
+                }
+            }
+
+            return true;
+        }
+    }
+}