That is not how it works, but it's an interesting idea. My worry is that it's a little fragile in the same way that vanilla git is fragile - you can accidentally start working on a new task and mess up your stack.
In reality, git-plan just keeps a directory of draft commit messages for you, and when you run `git plan commit` you can choose one of them to use as the template for your commit message. Essentially, it runs `git commit -t <YOUR_PLAN_FILE>`.
(I'm the author)