For the interfaces people use every day rather than visit once. Ten skills, and the whole kit is organized around a single idea: in a product UI, restraint is not a style preference, it’s the functional requirement. A flourish that delights on first encounter becomes a tax on the four-hundredth.
That’s why the motion phase is named for its constraint rather than its capability, and why the frequency gate does the most work of anything in this kit. It’s also why the signature-moment skills from the marketing kit are absent entirely — not a value judgment, just the wrong tool for a surface someone stares at for six hours.
The React phase is conditional and clearly marked. Skip it if you’re not on React; nothing else in the kit depends on it. The pre-ship phase leads with accessibility rather than ending with it, because custom widgets — the comboboxes, the virtualized tables, the command palettes — are where dense product UI reliably fails, and finding that out after everything is built is the expensive version.