To address the food safety issue: if you are selling the stuff, regulatory peeps in the U.S. find fault with farmers who don't have everyone wash their hands before going amongst crops. So, as long as you can train your chickens to wash their hands with
soap and
water after going to the bathroom and avoid dropping anything in your fresh leafy greens,, those people and their supporters will be happy. However, these rules are about sales and have a number of exempt categories, including normally cooked stuff and farms making less than $25K in 3 years. Not that you can't get in trouble if someone says they got sick from your farm, but you aren't required to follow certain protocols if you are exempt. As for the reality, critters run through fields, fly over fields, and eat out of fields, and plants are grown in the dirt. Studies have shown most bad stuff goes away in open air in healthy soil in a reasonable amount of time. Been a while since I got the details on the studies, but I was near ground zero when the sh*t hit the fan about lettuce around 10 years ago.
As for good
gardening hygiene, generally speaking, don't eat freshly pooped on leaves, especially raw. Don't fertilize, especially with a foliar spray, and right after harvest. If your using poop-based fertilizer, wash your hands before harvesting fresh leafy greens. Wait like 30 days or fertilize not the plant but in a place the plant can reach, or fertilize with things you can eat and won't spoil on the leaves, like
coffee to avoid bad things on a leaf. I think the standard in the industry might be up to like 90 days for fresh maneuer fertilizing leafy greens and like 30 on fruit
trees, but I haven't kept up. What I know is I got birds flying through the garden leaving presents regularly and I just harvest around those leaves and my biggest belly aches are from fish emulsion (that stuff is nasty) or too many sunchokes at once (high fiber food).
Good luck with the chickens!