Piero Bosio Social Web Site Personale

I would be very surprised if I posted a followers -only note that a non-follower could see.

If I posted a globally visible note in response to a followers-only note, and only the people who could see the original note could see my response, it would make sense to me.

Well, you asked what expectations were, and I told you. They're not what you seem to be proposing. Not sure what else to say.

Yes. That's equivalent to Alice setting their post followers only, and Bob setting their post public, but less confusing to the user.

(Edit: realized you hadn't said what Bob's visibility was set to. Anyway: UI quibbles aside, the answer is that you intersect the people who are able to view)

Yes. Either you do that or you ignore someone's privacy settings.

The intersection of Alice and Bob's followers.