I asked it to look at the code and come up with better factorings, but it failed. I ended up manually reworking several thousand lines of code myself, via my IDE. It took days.

I'd like a claude-of-the-future to be able to come up with beautiful ways to factor the code itself. Amongst the correct solutions, pick one which is conceptually simple. Write the code in a way that it makes subsequent changes easier to write. If I were doing RL with claude, I'd consider directing it toward solutions which allow subsequent changes to be implemented with as little effort as possible.