@evan A reply to any post is still a post and should be to whomever the replier chooses.

But I would agree with discussing/debating the following questions:
- In a reply, can the audience choice include a selection relative to the OP (instead of the replier)? Today this is not possible.
- Could multiple audiences be selected, such as the OP’s and the replier’s followers? (And what are the options for replies to that post?)
- What should be the default audience for a reply be when the reply is started?

@BrianJohnson I'd definitely recommend looking over my book from O'Reilly Media, "ActivityPub: Programming for the Social Web" for a good explanation on how replies work in ActivityPub.

https://evanp.me/activitypub-book/

@evan Fair enough, and I should have said “not implemented in Mastodon AFAIK”.

I’ll admit to not knowing all the ins and outs of what ActivityPub can do (vs a specific implementation). Philosophically, if implementing any cool or convenient feature means weakening the decentralized model, I’ll do without that feature. (Not saying that’s the case in this discussion, but it is where I start from.)

@BrianJohnson I should have been clearer. FO replies to FO posts in Mastodon go to the replier's followers. This means that FO conversations are only visible to people who follow OP and replier. It makes FO much less useful for personal conversations. I would like my colleagues at Mastodon to fix this!

@evan@cosocial.ca I'd say that follower only posts are a Mastodon-ism, and support for them should never be assumed.

To answer your original question,

• Should? Yes.
• If you have used "must" instead, I would've said "no, and good luck getting from here to there."

@julian no they're not! You can always address a Collection in AP. That's what followers-only means!

@evan@cosocial.ca hmm. I agree in the sense that any combination of recipients can be addressed, but the specific term "follower only" (to the exclusion of the public pseudo-user) isn't AP specific... could be wrong on that one.

Either way I do think it's a good courtesy to assume equal or narrower visibility when replying to any post. The specific issue you outlined in OP seems to be a Mastodon bug for sure.