OP, I'm so sorry. I think it's okay -- no, important -- to take a stand on this issue.
Two parents in my child's multi-ate preschool/K school have partnered with the director to educate and execute. This means that the parents invited someone from I think the city health board (???) first to talk with the teachers about how important this is (photos, the works--once you see what happens to a kid with these problems, it's no longer a theoretical issue) and to give very clear guidelines.
Next, information went out to parents over email, again and again. Whenever an offending food is found, an email goes out to all parents so everyone knows that XYZ is not allowed. This isn't intended to embarass anyone, and the "perpetrator"

isn't identified. The emails are to remind people and re-educate them. If Mr. A thinks a biscotti is okay, then there's probably a Ms. B and Ms C who are also unawares. This is ongoing. I think notes go into individual students' lunch boxes when it happens.
And finally, parents are invited to an allergy training at school. Again, pictures and so on will be used. If you care about your kid, you can imagine that all children are somone's little snowflake.

It's helpful to have everyone on board.
Now, this is a private school, so the director can stipulate her own policies a bit easier, I think. The culture is generally one of inclusion and helpfulness. When one parent balked (but my Joen NEEEEEDS to eat nuts), I understand that she said that mother was free to disenroll her child. The director would rather not have that kind of stupid drama.