While building I also create documentation in parallel. and md file in parallel also. like

Planning md - will have initial plan, goal, research, overview, tech stack.

Architecture md - will have all the architecture decision with reasons why we chose that.

each phase will have a separate documentation

all qa 1,2,3 will have md files noted everything.

deployement md, etc

I initally built these because - I can just change claude code to codex or new session anytime and giving access to the folder and it reads everything and can get updated on the current status.