Function
The lesson to un-mark
Whether the un-mark was saved
The learner's own undo of markLessonComplete, and the only thing that clears a mark — playback never does. Writes through the same tracker, so the outline, the lesson rows and the progress meters stop showing the lesson as complete without a reload; a refused save puts the mark back.
Deliberately not a hook: the completion toggle calls it from inside a transition, once the learner has confirmed.
Clears a lesson's completion for the signed-in learner.