Responding to constant snack requests right before dinner without turning food into a battle

Dinner is twenty minutes away, and my child asks for a snack for the fourth time. I don't want to make food a power struggle or ignore genuine hunger. On the other hand, a big snack now guarantees half the dinner will be left untouched. We're considering a predictable afternoon snack and a small option like fruit or vegetables close to dinner. How do you manage the timing without moralizing about ‘good’ and ‘bad’ foods?