Suppose there was a comment thread containing a back-and-forth conversation between a kbin.social user and a lemmy.world user. What would a user on beehaw.org see, given that they are federated with one but not the other?
I also wonder what would technically happen if beehaw users could not see comments from defederated instances in other instances. How would they see a back and forth? Would they see the same level of indentation? Would they see other users from federated instances replying to comments which do not exist?
So for a Beehaw user, would they see all of the the Kbinner's comments and it would look as if they were talking to themselves? Or would they only see the top level Kbinner comment and nothing else (due to their instance not seeing the Beehaw comment and therefore not seeing children of that comment either)?
Beehaw can pull in content from other instances, but users from those instances cannot comment or post back to Beehaw. If you were interacting with content coming from Beehaw on a different instance, in practice it would feel like you're shadow-banned as nobody on Beehaw would be able to see or reply to you.
There's two different scenarios, a community not hosted on beehaw:
they wouldn't see the chain at all.
On a community hosted on beehaw:
Message a would only exist on world's local copy of the thread, nobody not on world can see it. (This local copy is also not getting updated by anyone not on world.)
Basically, the true thread exists on the instance that hosts the community. Defederation cuts off communication with one server. If it's the server that hosts it, it's a lot more severe.