Can there be a compound which stops the pesticide from entering into the fruit or vegetable? For example, a solution which is sprayed before pesticides and somehow blocks pesticides from entering into the fruit?
In addition to all the qualities @Karl stated (harmless, edible, overspray decomposes, etc.), such a coating would also need to stretch as the produce grows. Such a protective covering might even obviate the need for pesticides, if it were to be created.
That said, there are edible wax and protein coatings to preserve produce after it's picked. Unfortunately, these are applied after pesticides may have been sprayed on the food, so one hopes that the produce is washed before spraying seals in toxins.