How long until phones are so not controlled by their users any more, that it becomes a plausible defence to say “that wasn’t me, it must have been the <app or O

How long until phones are so not controlled by their users any more, that it becomes a plausible defence to say “that wasn’t me, it must have been the <app or OS vendor> that caused my device to do it”? Conversely, how might Apple implement non-repudiation of user actions? If they control the platform utterly, how can they prove that a user really did something?