More than you get from one lemonade, for a healthy person. Not much less than the FDA recommended maximum per day if we’re talking about the largest size, but the gap between “maximum recommended” and overdose is a reasonable bit. If you’ve ever known someone to drink more than four cups of coffee, or as many energy drinks (or as few as 2 for certain brands), you’ve known someone who exceeded the recommended maximum. You have to go a fair bit past it to have acute issues if you are otherwise healthy.

If you have a medical condition that restricts your diet, it is on you to know what you can and cannot have and on the restaurant to make it clear when something unexpected might contain the thing. I’d argue Panera, by analogizing the amount of caffeine to an equivalent volume of coffee and also giving the explicit numerical amount in each size the drink was offered in did that.

Imagine someone suing a restaurant because they ordered a dish that contains shellfish and they have a shellfish allergy. The menu spelled out that it contained shrimp, but how is anyone supposed to know that shrimp is shellfish?