Ping @angus, thought it might be useful to you to read the experiences of a bunch of fediverse newbies with a Discourse instance, trying to get their heads around how to use the AP federation features;
There may be a few specific things you can address, like whether posts deleted on a fediverse server are supposed to persist on a Discourse forum hosting the thread they were part of. Or whether or not Followers-Only replies to topics federated from a Discourse forum can be publicly displayed on that forum. If those are not expected behaviour, they may have found bugs.
It may be that post deletes and recognising posting scopes are features that haven't been implemented yet, in which case I'd suggest making them a high priority. There's a subset of the fediverse community who can be very prickly towards devs they perceive as failing to prioritise privacy and consent. They can even get agitated about public posts appearing outside the fediverse (as they understand its boundaries). See the flack BridgyFed's fediverse<>ATmosphere bridge got ,over being opt-out, rather than opt-in on both ends.
Anyway, thanks for the ongoing work to bring Discourse into the fediverse. Hope you enjoy interacting with the cool folks working on bringing more music hosting platforms into the fediverse, in an artist-centric way : )
AFAIK in Mastodon deleted messages don’t be deleted in Discourse. Deletion is restricted action in Discourse. And Discourse isn’t a Mastodon instance. Discourse is using ActivityPub. Different thing.
And every Mastodon user knows, or should know, that deletion is very unreliable. It spreads thru Fediverse or not.
Forum is forum and ActivityPub (practically only Mastodon from Discourse point of view) is its own thing.
By Followers-Only you mean ”Publish Post #1 and deliver it to the followers of the Group Actors” (or normally after 5 mins) for OP? Answer for such topic isn’t going to followers, into global public timeline. It is just matter of which timeline someone sees messages.
It just means it is subscribed feed as normally in Mastodon. Nothing secret.
When someone answers (which happens really rarely because of group actors and how they boosts, but so it works nowadays) to a topic from Mastodon, it is a public message in that forum and in Mastodon, as usual. And if someone from forum answers to that comment, not into topic (thing, that forum users don’t realize) mentioning that Mastodon user, that post is totally public and be federated just normally.
Or did I totally misunderstand your question?
This is different thing and worth of its own topic, but my opinion is that nothing should do or happen just because of some subset wants something, that is beyong normal limit, or they are using theirs own definition. Meaning that nothing above isn’t matter of consent or privacy.