I've been trying to solve the issue of how to look up posts from a lemmy post in mastodon.
The true posts are hosted on the home instance of the person.
I have posted a comment on a lemmy.world community. Someone from kbin.social responded to me, I am from crystals.rest.
Searching for the main post cannot find it from the cached copies. When you browse communities from your home instance over to ones that are remote, you get a copy, but it's not a truely federated copy, which sort of makes sense, but mastodon and others are able to populate from the cached copy properly from other mastodon instances (and most others).
So when you search for it on mastodon, you get the main post, but there's no comments. I was trying to grab one of my comments to boost it possibly, and was having trouble. I thought I should copy the link to my post with lemmy.ml, because it's a comment from there? Wrong, I have to copy the link to the comment from crystals.rest! If you search for the main post again, it will show my comment, it's now discovered it! But it doesn't show any replies from anyone! But I had one, so I followed the same logic, I had to copy the url of the comment from kbin.social, and when I found it, now the main post has our comment chain.
You have to get the link to EVERY comment to get it to populate, and the true links to the comments come from their host instance, which does make sense, but it's unable to fetch them like a mastodon post just grabs all replies available to them through federation. Lemmy itself doesn't even grab most of the comments from other lemmys very consistently, in a timely manner, even if you are already federated and have interacted with it.
Once I post this, I have followed my lemmy account on my mastodon one, and see if I do actually get post updates, as once it populated a reply, and other times, it doesn't populate a reply. It seems I haven't full found myself. And I've followed this community, but it hasn't given me a post update.
Edit: It has not shown the community post after about 5 minutes. (Also for reference if linked elsewhere, my site is very small so should not be long to find) Also even though I've followed my lemmy account, it will not show me new replies. It seems possibly the follower's hook is not implemented because you can't follow people on lemmy natively.
Also interesting, is that the main post did get shown on calckey! And if you copy the url of the calckey post into mastodon.art, it will find it. Still can't find the replies thou.