[kiitos]

    func bar() error {
        err := baz.Transmogrify()
        return fmt.Errorf("bar: %w", err)
    }

This is broken. If baz.Transmogrify() returns a nil error, bar will return a non-nil error.

Also, annotations like this, which repeat the name of the function, are backwards. The caller knows the function they called, they can include that information if they choose. Annotations should only include information which callers don't have access to, in this case that would be "transmogrify".

The correct version of this code would be something like the following.

    func main() {
        fmt.Printf("err=%v\n", foo())
    }
    
    func foo() error {
        if err := bar(); err != nil {
            return fmt.Errorf("bar: %w", err)
        }
        return nil
    }
    
    func bar() error {
        if err := baz.Transmogrify(); err != nil {
            return fmt.Errorf("transmogrify: %w", err)
        }
        return nil
    }