Pretty screens that confuse people are expensive art. We design interfaces around what users are trying to do — tested on real people before developers write a line.
UX is whether the user gets what they came for; UI is the surface they do it through. Sold separately they're jargon — done properly they're one process.
Yes, and it's non-negotiable on product work. Five moderated sessions catch the majority of usability problems and cost far less than one wrong release cycle.
That's the default. We hand off systems and specs, join sprint reviews during build, and stay available for the edge cases mocks never cover.