I wrote a 20,000 line multiplayer battle-arena game in XNA back in 2015 with manually coded physics (so everything is there in the code) and have tried several times with Claude, Gemini, Grok, DeepSeek, and GPT to translate it to JavaScript.

They all fail massively 100% of the time. Even if I break it down into chunks once they get to the chunks that matter the most (i.e. physics, collision detection and resolution, event handling and game logic) they all break down horribly and no amount of prompting back and forth will fix it.