I'm sorry, but it is entirely unreasonable to put whether or not you live or die in the hands of a minimum wage service worker. If a sip of milk or a bit of egg would kill you, you need to prepare your own food.
While I agree service jobs deserve a lot more pay and better training, it just isn't fair to put a person's literal life in the hands of someone who just signed up to serve coffee. They didn't sign up for that responsibility.
The problem is that many people don't know how's severe they have it until it's too late. Some people develop/find allergies as babies and might go years or decades without touching the stuff. Sometimes the allergy disappears, sometimes it gets letally worse.
You would think a cafe worker would have been trained to make any of their drinks from the five or six milk alternatives when requested
You would expect a food service worker to have been thoroughly trained in serving customers with allergies
The worker's allergy training was a self paced, at home, online course and quiz. That's not enough to ensure your staff don't accidentally kill the customers
If you have an allergy to milk so severe you'll die, you're probably just gonna die. Unless you only eat what you or mom prepared.
It's not about training, mistakes happen. If NASA engineers make mistakes that crash billion dollar spacecraft, you'd better believe the folks who make your food are going to make mistakes. Don't put your life in their hands.