I'm in the "never reveal your plans to the enemy" camp on this one--it's none of their business if you're looking for another job, so I would leave that out of any conversation. Also, retaliation can be common with some employers, especially if you bring up the ADA and claim a disability because of celiac disease. I was a corporate paralegal for 5 years and handled employment claims against some major USA companies, and I've seen it all--even by huge companies that contract with the government that should know better. I say keep your cards close to your vest, wear an N95 mask if you handle wheat flour, and quietly look for another job if you feel you can't continue there. 

@ohmichael doesn't have an official diagnosis of celiac disease yet. That would need to happen if he were to pursue a disability claim.

This article might be helpful. It breaks down each type of test, and what a positive results means in terms of the probability that you might have celiac disease. According to this article your two positive DGP-IgA tests mean:  

This is so very interesting I love all this information, knowledge is so very important for us to help ourselves heal, I have been so wrapped up with my dogs nutrition after vets told me she needed a operation, which turns out I can help with this for her  myself also , I may have been missing the tap on the shoulder to say integration into your own health is needed here too , although I have been aware I must admit myself has been on the back burner at times , I also have a granddaughter with nut allergy I researched for that , this is now screaming at me to turn inward to myself also , and deal with my invisible struggles I also am carrying, thankyou for all the information keep it coming , my ears and eyes are fully open 🙏

"Celiac disease can be considered a disability under the Americans with Disabilities Act (ADA) if it substantially limits one or more major life activities, including working. Employers are required to provide reasonable accommodations to qualified individuals with disabilities, which may include modifications to the work environment or adjustments in work schedules to accommodate the dietary needs of employees with celiac disease." So until you find a new job, I would think your current employer can and should and is legally required to accommodate you by not having you stock flour products. There's a lot more other work that needs to be done in a grocery.  Speak with them, be honest, tell them your plans, ask for their cooperation until you can find another job.