Mosaic UI

Two things live under Mosaic, and this skill covers the how-to for both:

• Styled components are authored with StyleX — stylex.create declares the styles, themeProps emits the part's public identity (the .cl-<slot> class plus data-<axis> attrs), and mergeStyleProps fuses the two with the props the part was called with. A part takes xstyle (StyleX atoms for its root), never className/style.
• Flows follow a model → controller → view split — where the data comes from → what the user is doing to it → what that looks like. What crosses each boundary is plain data: no Clerk resource reaches the controller, no machine snapshot reaches the view.

model       Clerk adapter: reads Clerk hooks and resources, resolves the
            environment, gates permissions, and answers with plain data plus
            plain callbacks under an explicit `status`. The only layer that may
            import Clerk hooks or call Clerk resource methods.