Tokens, states, and accessibility checks that stop the handoff from becoming a second design process.
Handoff fails when files show only the happy path. We require empty, loading, error, and permission states before engineering estimates a screen.
Shared tokens for type, space, and color keep the website and the app related even when they ship on different calendars. We would rather a smaller token set used everywhere than a perfect file used once.
Accessibility is part of the definition of done: contrast, keyboard paths, and labels. Fixing it after launch is slower and less kind to users.
