The nature and direction of the crack indicates it was caused by the extended mast being pulled back too hard or too often, or a combination, leading to a stress crack.

If a correct-fitting seatpost bridged this with at least 3" below, it shouldn't have cracked. So you have to consider possibilities because unless you identify and eliminate the cause of excess stress there's no way your repair will hold.

Possibly the seatpost is undersized or is too flexible, allowing movement, especially with a heavy rider or rough service in mtb or crappy roads. Check by painting brittle nail polish across the crack at the front, installing the post and levering it backward. If you can crack the nail polish your repair will also fail. If necessary buy a more rigid seatpost and try again.

Then to get any kind of reliable repair you'll have to do figure 8 wraps of the glass encompassing the top tube to get any kind of structure.