Comment by hleichsenring

A plan lives in one session and is gone afterwards. A spec is a file in the repo. It gets reviewed against the actual code before anything is built, its definition of done is checked when the change is committed, and it stays there with the decisions behind it.

The next agent reads what was built before and why. And because it has a fixed format and workflow, everyone on a team works the same way, instead of each developer prompting their own plans.