[Bug]: replies not federating when no one subscribed to community

[Die4Ever]

Requirements

• [x] Is this a bug report? For questions or discussions use https://lemmy.ml/c/lemmy_support or the matrix chat.
• [x] Did you check to see if this issue already exists?
• [x] Is this only a single bug? Do not put multiple bugs in one issue.
• [x] Do you agree to follow the rules in our Code of Conduct?
• [x] Is this a backend issue? Use the lemmy-ui repo for UI / frontend issues.

Summary

Someone replied to my post/comment and I didn't see it on my own instance since I am not subscribed to the community and no one else in my instance is subscribed either. Searching for the comment by URL does cause it to federate. I've seen this happen twice in the same post.

Steps to Reproduce

1. Post or comment in community your instance is not subscribed to.
2. People reply.
3. You don't see the replies or get notifications, you have to open the post from a different instance.

Technical Details

The post from my instance's perspective: https://retrolemmy.com/post/16368817 (I will not respond, so that this bug report is intact)

Instance of the community: https://rss.ponder.cat/post/147589/17763

Previously I had to manually search for the URL https://ponder.cat/comment/2542342 so I was able to reply to that, then we he replied again it never showed up on my instance so I decided to make this bug report instead of searching it to force it to federate.

Version

0.19.10 and 0.19.5

Lemmy Instance URL

https://retrolemmy.com/post/16368817

[Nutomic]

This is intentional, without this check a malicious instance could spam you with hundreds of posts and comments. But the check could probably be relaxed to accept activities from instances that you are already federated with.

https://github.com/LemmyNet/lemmy/blob/main/crates/apub/src/activities/community/announce.rs#L215