The idea of writing a commit message in advance is nice, and possibly helpful in focusing, but I don't understand the added value with respect to the issue stat

The idea of writing a commit message in advance is nice, and possibly helpful in focusing, but I don't understand the added value with respect to the issue stated. Commit messages aren't the challenge, rather it is planning out what goes into a commit. As many others have said there are already great UIs to help you manage these things retroactively, but there is probably no good substitute to properly planning your work and executing on that plan (if order is your top priority)