Ya, openclaw is overkill for rewriting a codebase, especially when you're paying API costs.
I developed my own task tracker (github.com/kfcafe/beans), i'm not sure how portable it is; it's been a while since i've used it in claude code. I've been using pi-coding-agent the past few months, highly recommend, it's what's openclaw is built on top of. Anthropic hasn't shut down Oauth, they just say that it's banned outside of Claude Code. I'd recommend installing pi, tell it what you were doing with openclaw and have it port all of the information over to the installation of pi.
you could also check out ralph wiggum loops, could be a good way to rewrite the codebase. just write a prompt describing what you want done, and write a bash loop calling claude's cli pointed at the prompt file. the agent should run on a loop until until you decide to stop it. also not the most efficient usage of tokens, but at least you will be using Claude Pro and not spending money on API calls.
I'm kinda doing this in a back-and-forth way over each section with openclaw, and one nice thing is that I've got it including the chat log for changes with each commit. I'm happy about how it's handled my personality as needing to understand all the changes it's making before committing. So I kind of want something interactive like that -- this isn't a codebase I can trust an LLM to just fire and forget (as evidenced by some massive misunderstandings about rewiring message strings and parameter names like "_meta" and ".meta" and "_META" that meant completely different things which the LLM accidentally crossed and merged at some point, before I caught it and forced it to untangle the whole mess -- which it only did well because there were good logs).
I sort of do need something with persistent memory and personality... or a way to persist it without spending a lot of time trying to bring it back up to speed... it's not exactly specific tasks being tracked, I need it to have a fairly good grasp on the entire ecosystem.