I've been doing a version of this in a side project. Instead of saving the prompt directly, I have a road map. When implementing features, I tell it to brainstorm implementation for the road map. When fixing a bug, I tell it to brainstorm fixes from the roadmap. There's some back and forth, and then it writes a slice that is committed. Then, I look it over, verify scope, and it makes a plan (also committed). Then it generates work logs as it codes.

My prompts are literally "brainstorm next slice" or "brainstorm how to fix this bug" or "talk me through trades offs of approach A Vs B" so those prompts aren't meaningful in their own.

It's quite effective, but I'm a team of one.

I agree with this, I like spec-driven-development tooling partially for this reason. That being said, what I’ve found is often that I don’t include enough of the “why” in my prompt artifacts. The “what” and “how” are pretty well covered but sometimes I find myself looking back at them thinking “Why did I do this?” I’ve started including it but it does sometimes feel weird because I feel like “Why would the LLM ‘care’ about this story?”

I wonder how scalable that is. After the twentieth feature has been added, how much connection will the conversation about the first feature still have with the current code? And you’ll need a larger and larger context for the LLM to grok the history; or you’ll have to have it rewrite it in shorter form, but that has the same failure modes why we can’t just have it maintain complete documentation (obviating the need to keep a history) in the first place.