You could do the gustav init on your prd, then ask it to cross reference the sprint planning with your actual codebase and mark features that have been completed as done.

Its not tested on projects already going... but clone your repo in a different folder and try it :)

Thats the warrior spirit

This was a fun read! Started at your part 1 of course. I recognize a lot (if not everything) you describe. I have been chasing the high of a satisfying **working** workflow in Claude Code for ages. It has become sort of a hobby I guess :p