After forgetting to place the yeast starter in the fridge overnight I placed it in the freezer this morning for a short while to do a quick cool crash. I misjudged the time and the water above the yeast cake has begun turning into a frozen slurry - though it is not completely frozen. I had a 1.1L starter in the freezer at -17ºC for roughly 1 and 3/4 hours.
I've read on other questions that if frozen it will rupture cell walls and viability will have been seriously affected. Given that this did not completely freeze over am I OK to brew? At what point during freezing is yeast ruined?