Read the defrag code in other well-established fs like ext4 or btrfs. They all have limitations(or caveats, if you will). It's one of those problems where you just have to throw money at it and hope for the best. Even Microsoft kinda just gave up on it because it's really a pointless exercise at this point in time and age.
I did the same. Was genuinely curious. Didn't get much from it. I'm still confused.
The code base is huge for an LLM to handle, perhaps it was generated over multiple prompts idk. Not sure if someone can train a model on the kernel code or exfatprogs and generate the code. I doubt someone with such expertise would even go through the process when they can just write the code themselves which is much easier.