What is the standard of review for a due process notice issue?

We review a due process notice issue as a mixed question of law and fact in which we defer to the juvenile court's findings of historical fact under the substantial evidence standard of review and determine a due process violation under the de novo standard of review. (Cf. People v. Alvarez (1996) 14 Cal.4th 155, 182 [review of search and seizure issue]; see In re J.H., supra, 158 Cal.App.4th at p. 183 [constitutional issues reviewed de novo].)