Everything the Studio sheet shows — design tokens, presets, the package registry and snippets — behind one behaviour, so the panel is written once and the source can change underneath it.

ADR-10. The default is MishkaCmsCore.Runtime.PageBuilder.Marketplace.Kits, which answers out of what is really on this server: its tokens are the site's own stylesheet declarations, its packages are the kit components on disk this site has NOT installed, and installing one runs the same dependency closure the first-run wizard does.

It used to default to Mock — the design prototype's seed data — on the reasoning that a tab rendering its real, empty answer looks broken rather than unfinished. That reasoning outlived its truth. Three of the four questions now have real answers, so the sample catalogue was showing invented packages with prices beside an Install button that refuses, and invented presets beside an Apply that only flashes. An honest empty state is worth more than a convincing one that lies; the Presets tab says what it is missing and why.

Mock is still here and still opt-in, because the prototype's seed data is what the design was drawn against:

config :mishka_cms_core, :builder_marketplace,
  MishkaCmsCore.Runtime.PageBuilder.Marketplace.Mock

A remote registry later is the same config change, not a UI change. The precedent is UiKitHandler.ensure_bundle!/1, which already does local-first-then-fetch for the component bundles.

config :mishka_cms_core, :builder_marketplace, MyApp.RealMarketplace

Token generators are real

The four export formats are not mock-ups. generate/2 emits a genuine tailwind.config.js theme.extend, a :root custom-property block, a W3C design-tokens JSON document and an Elixir theme module — ported line-for-line from the prototype's own generators. That is what makes the Studio's Copy button worth having before any backend exists.