@evan Oh, I know. It makes keeping tabs on people wishing to be quiet or unseen more visible. It really breaks the "for followers only" intent a badly broken promise and rather dishonest at the worst and poorly (or not even) thought through at the lightest.
@vanderwal so, I think I see where we went askew here.
You said, "Most services get this wrong and make the replies visible to B's followers only."
I disagreed, "Most services get this *right* and make the replies visible to A's followers only."
I don't think we disagree about the right way to do it -- we disagree if services actually do it that way.
I am not sure why you think they don't. As far as I can tell, X, Instagram and Facebook all make replies visible to A's followers.
@evan Twitter / X have public replies from B visible to A's followers as they are open. But, B's followers can see the response, which is where things get to be problematic.
I wasn't intending to say only B's followers saw the reply, but that they could see the response to a private account.
Marketers, stalkers, and worse have easy pickings in that model.
What @dahukanna lays out in the venn diagram is the good approach.