This @tailscale article on Nat Traversal has been open in my tabs for months. I've finally made it to the end and my goodness it's a good read! The internet is wild, and frankly I think this blog post needs to be an open source library. It's a powerful understanding that I've only seen parts of in #p2p libraries. But I got to be honest, I might not have understood it before even if I saw it.
Good read, 11/10 article, thank you @danderson