“Cross-contamination” in the kitchen can be just as lethal as eating the offending food.
Best to alert the wait staff immediately.....some restaurants have become very aware of the issues with allergies.
That is why we do not eat at restaurants very much anymore. Too many bad experiences have convinced us that in general it is just too risky for my wife. There is also the issue of ingredients such as worcestershire sauce and others which most people do not realize are partially made from fish products.