ok, less than 20 minutes after hearing about the Alex drama, here is my take:
Does mentionless replies break the ActivityPub spec? Let's find out...
No! No they don't! Alex is following the ActivityPub spec that we all decided to use!
"But it broke my implementation!"
No, it exposed a bug in your implementation. Were you seriously parsing messages from remote servers for addressing information?
I will now accept my egging for missing some glaring thing I missed.
btw, what were you expecting when/if Some Enormous Fucking Website exposes an ActivityPub endpoint for their past 10-20 years of post data (YouTube, maybe) and the comments are replies to the video that **don't have mentions of the video author's username**? Or simply, all the posts don't have mentions for every user involved in the thread because that's Twitter behavior that started from Twitter and only makes sense on Twitter and Twitter clones?
"pissed everyone off in literally record time" - Recommended by 10 out of 10 people who, for some sad reason, have a dedicated column up to watch #fediblock.