I deleted the history while doing maintenance on the site. Specifically, I was cloning Discourse into a fresh repository and removed the old one. I didn’t realize that Discourse stores backups and site state within the repository checkout, so removing the old repository removed the history.
I’m currently setting up uploading backups off the machine to prevent this from happening in the future.
Haha, it happens.
I just created the account to join the discussion. I guess I’m one of the early users of the new forum now 
Better it happen early in the history of the forum than later 
C’est la vie! We can consider it a good forcing function for backups 
I had your answer opened for a long time since I wanted to get to it “eventually”
p.s.: good it’s backed up by Google cache, copying to the gist http://webcache.googleusercontent.com/search?client=ubuntu&channel=fs&q=cache%3Ahttps%3A%2F%2Fdiscourse.dhall-lang.org%2Ft%2Fdesign-question-configuring-predicate-via-dhall-file%2F43&ie=utf-8&oe=utf-8
I’ve noticed that you can still find some of the deleted threads and their cached contents via this Google search: https://www.google.de/search?q=site%3Adiscourse.dhall-lang.org/t/