"hot" joins will use internal ids (relations, like/share, addressing) while "slow" relations will use full ap ids (attributed to, context, user configs)
i think it's all of them? constructors are still weird
old ones from mastodon's blog weren't that useful since all objects/activities are traits in the end
actor, webfinger, activity, object thanks gargron https://blog.joinmastodon.org/2018/06/how-to-implement-a-basic-activitypub-server/