had that happen once just like yours and took a bolt extractor with a long extension and taped it with duct tape. tapped on it with a hammer to barely get it seated and violy, the spark plug came out. put a new one in…
the spark plug didn’t snap easily. it was stuck pretty good. i resorted to using a breaker bar and after 2 rotations, it snapped. so a bolt extractor wasn’t gonna help. sighs. letting a machinist handle it.