They are asking candidates to do work in their repo and taking it to prod? That feels odd.

'We are extracting free labour from employment candidates, it is great for us'.

Why not go a step further, and add a fee to become a candidate? Or perhaps just to skirt the queue and get to the front of the line?

Edit: Then there's the industrial espionage aspect but I don't really care about that, it's probably for the best if competitors and curious folks interview with them to learn what they have and how it works and undermine their business.

There are “a few odd” things here. It is not entirely clear if this is sort of a rage bait blog post as well. What looks to me they do not even care if you are good “engineer” rather look for prompters and then use their contributions to improve their own platform; many of us have automation templates for that which would be difficult to replicate. I am not even talking about the mention of JS to do that, like sure it is easier because your platform does not need to compile, but if they move huge amounts of money and JS is actually used for it, you’d expect someone to understand how VM interprets that code etc. IMO it is possible (such interview practice) purely because it is a tough job market now.