> What is even the downside of adding a few extra characters to the end of a comment to show who wrote it?

You're right - in fact we should do this for every line of code, so that we know of whom to ask questions!

    func main() { // jen20
        fmt.Println("Hello World") // ziml77
    } // jen20

What's the downside of adding a few extra characters!?

Of course, this view is already available to people: `git blame` - and it's the same for comments, so there is no need.

The exception is "notes to future self" during the development of a feature (to be removed before review), in which case the most useful place for them to appear is at the _start_ of the comment with a marker:

    // TODO(jen20): also implement function X for type Y

Then they are easy to find...