So “no manipulation” or “maintaining human free will” seems to require a form of indifference: we want the AI to know how its actions affect our decisions, but not take that influence into account when choosing those actions.
I think the butler can take that influence into account in making its choices, but still reduce its manipulativity by explaining to Petrov what it knows about how breakfast will affect Petrov’s later choices. When they’re on equal epistemic footing, Petrov can also take that information into account, and perhaps choose to deliberately resist the influence of breakfast, if he doesn’t endorse it. Of course, there are limits to how much explanation is possible across a substantial intelligence gap between AI and people, so this doesn’t dissolve manipulation entirely.
I think the butler can take that influence into account in making its choices, but still reduce its manipulativity by explaining to Petrov what it knows about how breakfast will affect Petrov’s later choices. When they’re on equal epistemic footing, Petrov can also take that information into account, and perhaps choose to deliberately resist the influence of breakfast, if he doesn’t endorse it. Of course, there are limits to how much explanation is possible across a substantial intelligence gap between AI and people, so this doesn’t dissolve manipulation entirely.