Is the trolley scenario intended as a blame-finding simulation? I thought it was more like “what (ethical) choice do you make in a difficult situation” deal.

You surely still have some agency after your brakes failed. Or at least if it happened to me I wouldn’t let go of the wheel to find out if I hit group A or B, confident in the knowledge that who or whatever I plow into it is not my fault and all choices from that point are equal.