What do you notice about the comments on this post? https://piefed.social/post/555259
The post was made in the news@lemmy.world community and other posts linking to the same news article were made in technology@lemmy.world and in askusa@discuss.online. 3 different posts in 3 different communities.
PieFed de-duplicates them and only shows the post once in the timeline and when viewing the post all the comments on those 3 posts are shown in one place.
The fragmentation problem is solved.
Yes, url is the only reliable way I could think of to match posts.
For image posts we could use a hash of the image data. But image cross-posts are not common so it doesn’t seem urgent.
You could add linking to the same post, eg crossposting, to the criteria.
The urge to switch my server to piefed grows bigger every day.