My use case is a little different (mostly prototyping and building design ops tools) but +1 to this flow.

At this point, I typically do an LLM-readme at the branch level to document both planning and progress. At the project level I've started having it dump (and organize) everything in a work-focused Obsidian vault. This way I end up with cross-project resources in one place, it doesn't bloat my repos, and it can be used by other agents from where it is.