Who should ultimately be responsible if a person had a food allergy and a server or clerk messes up and serves that person the very item they are allergic to?

Inspired by another question.
I was at a seafood restaurant with a friend and she told the waiter she was highly allergic to shellfish, even the spatula couldn’t touch the shellfish and then her food. She really emphasized it, and he took her seriously and came back to assure her a clean spatula was used. She was fine after the meal. But I thought at the time that I probably would not go to a place that served shellfish and risk my life on a cook or server that was not careful.
Who should be responsible for ensuring their allergies are taken care of? You or others?