I\'m wondering if it is possible to build git commit messages incrementally, documenting what I\'m doing as I make code changes:
You are supposed to do a commit for every small change you do that requires a message. This is especially easy with a distributed versioning system like git that you are using.
And if you for some reason dislike this pattern and want to do the way you described, just use notepad and append to your message after coding a while and then copy paste it when commiting.