Use Magit and Emacs with git-duet

magit-duet-commit.el

(require 'dash)
(require 'magit)

(defvar magit-duet--default-commit-popup-actions nil
  "Store the magit-commit-popup here for
 de-initializing. magit-duet-commit")

(defun magit-duet-commit (&optional args)
  "Create a new duet commit"
  (interactive (if current-prefix-arg
                   (list (cons "--amend" (magit-commit-arguments)))
                 (list (magit-commit-arguments))))
  (when (setq args (magit-commit-assert args))
    (magit-run-git-with-editor "duet-commit" args)))

(defun magit-duet-commit-init ()
  "Add duet-commit to magit commit popup.."
  (interactive)
  (when (eq magit-duet--default-commit-popup-actions nil)
    (setq magit-duet--default-commit-popup-actions
          (plist-get magit-commit-popup :actions))
    (plist-put
     magit-commit-popup
     :actions
     (-remove-at 5 (-insert-at 4
                               '(100 "Duet commit" magit-duet-commit)
                               (plist-get magit-commit-popup :actions))))))

(add-hook 'magit-mode-hook 'magit-duet-commit-init)