I remember seeing advice, years ago, to let lettuce sit in a weak bleach solution before use. But I doubt that’s ever been followed by many people. Current advice (at least at home) seems to be to rinse lettuce to remove dirt ( https://hgic.clemson.edu/factsheet/safe-handling-of-lettuce-... ). Apparently most health problems from lettuce are on the surface and not particularly hard to get off.

Which wouldn’t help in this case. It seems like it is time to irradiate produce.

Or just, you know, grow it in a clean manner, and not turn it into an ultra processed food?

I wouldn't classify bagged salad as an ultra processed food as it's usually just cut and cleaned leaves from the various ingredients. It's not like they pour all the leaves into a machine and get soylent green out of the other end.

This depends on the food and the disease/pesticide in question.