This callback is called exactly the same way it was previously - just with different UI logic.    See `src/plugins/expressions/public/render.ts` line 68.    We used to use `defaultRenderErrorHandler` before, and it would output the errors as toasts. Since we now pass a custom error handler - it gets called instead when an error occurs.    There are no other changes in flow. I just extracted the state handling into meaningful callbacks to make it more readable.