Figma, and the platform underneath
Day to day the file is Figma: frames, components, text styles, and a prototype of the paths that matter. When you already have a library, we add to it. Notes sit on the screen they explain.
Platform rules live in the frames. On iPhone and iPad, type has to grow, and a Home Screen widget is a separate layout when the product has a reason to be there. On Apple TV the type is larger and focus replaces the tap. On Android the back gesture and the system bars belong to the screen. On the web we design keyboard focus, a narrow width, and a slow connection.
Contrast, a name on each control, focus order, and a target large enough to hit are the same pass, not a later audit. We implement the technical side of WCAG. We do not certify compliance, and the file alone does not make a shipped product conform. A second language needs room for longer labels, and a chosen place for the switch. An offline screen says it is offline.