Tell HN: What we did about expired links

Earlier today, a user asked [1]:

What is it about Arc that causes the [expired] link issue? I know very little about Arc. But I understand it to be a language, whereas the issue you describe appears to be the function of some implementation decision. Can you please elaborate?

I replied, and a few people thought it should be its own post. It's too long for here, so it's at http://pastebin.com/bSW5dfRQ.

1. https://news.ycombinator.com/item?id=8423482