I also think that might not be everything you need to really vet/recreate those PRs since there's a lot of strategic and operational stuff that goes into the pre-composition runs (sometimes I actually throw everything away and restart), so something a little more sophisticated would be interesting.
However, having a rigorous spec process which ends up giving lots of details to the agent seems to me the right way to build stuff with LLMs. Rather than iterating and piling changes after changes.