By Vishnuu Gullipalli   A missing pack of cereal. An empty spot where a soda should be. To a shopper, it feels like a small frustration. To a brand, it’s a silent loss. And for retailers juggling thousands of products across thousands of stores, those empty spaces add up fast. For decades, on-shelf availability has been treated as a logistical headache, something field reps and store managers tried to patch together with manual checks, phone calls, and best guesses. But in reality, the shelf has always been the final frontier...