Simple implementation of hybrid game objects - entity in unity ECS

CompanionObjectAuthoring.cs

// Spawns a game object and link it to the entity this component is attached to.
// The linked game object will have the local transform of the entity copied to its transform automatically by the system
// Any additional monobehaviour can be made accessible from the ECS world by implementing the ICompanionComponent interface
//
// Note: Game Object / Entity destruction is not handled in this gist
public class CompanionObjectAuthoring : MonoBehaviour {
    [SerializeField] GameObject prefab;

    class Baker : Baker<CompanionObjectAuthoring> {
        public override void Bake(CompanionObjectAuthoring authoring) {
            Entity e = GetEntity(TransformUsageFlags.Dynamic);
            AddComponent(e, new CompanionObjectPrefab {
                reference = authoring.prefab,
            });
        }
    }
}
 
public struct CompanionObject : IComponentData {
    public UnityObjectRef<GameObject> reference;
    public GameObject GameObject => reference.Value;
}

public struct CompanionObjectPrefab : IComponentData {
    public UnityObjectRef<GameObject> reference;
    public GameObject Prefab => reference.Value;
}

public interface ICompanionComponent {
    void CreateCompanionComponent(EntityCommandBuffer ecb, Entity entity);
}

public partial class CompanionObjectSystemGroup : ComponentSystemGroup {}

[UpdateInGroup(typeof(CompanionObjectInitializeSystemGroup))]
public partial struct InstantiateCompanionObjectSystem : ISystem {
    public void OnUpdate(ref SystemState state) {
        EntityCommandBuffer ecb = new(state.WorldUpdateAllocator);

        foreach ((CompanionObjectPrefab companionObjectPrefab, Entity e) 
                 in SystemAPI.Query<CompanionObjectPrefab>().WithNone<CompanionObject>().WithEntityAccess()) {
            InstantiateCompanionObject(companionObjectPrefab.Prefab, ecb, e);
        }

        ecb.Playback(state.EntityManager);
    }

    static void InstantiateCompanionObject(GameObject prefab, EntityCommandBuffer ecb, Entity e) {
        GameObject companion = Object.Instantiate(prefab);
        ecb.AddComponent(e, new CompanionObject { reference = companion });

        foreach (ICompanionComponent companionComponent in companion.GetComponents<ICompanionComponent>()) {
            companionComponent.CreateCompanionComponent(ecb, e);
        }
    }
}

public partial class SyncTransformSystem : SystemBase {
    protected override void OnUpdate() {
        foreach ((RefRO<LocalTransform> localTransform, CompanionObject companionObject) 
                 in SystemAPI.Query<RefRO<LocalTransform>, CompanionObject>()) {
            SyncTransform(companionObject.GameObject, localTransform.ValueRO);
        }
    }

    void SyncTransform(GameObject companionObject, in LocalTransform localTransform) {
        companionObject.transform.position = localTransform.Position;
        companionObject.transform.rotation = localTransform.Rotation;
        companionObject.transform.localScale = Vector3.one * localTransform.Scale;
    }
}