It's a tool called Drawd (drawd.app). You upload screen mockups onto an infinite canvas, draw rectangles over tap areas to define hotspots, then connect screens with arrows to map the navigation flow. Each hotspot carries an action type — navigate, API call, modal, conditional branch. When you're done, it exports structured markdown files (screen inventory, navigation map, build guide) that you feed to the LLM as context. The visual step is what catches gaps before you burn tokens on a broken spec.