Design System API

Design System API gives Drupal a shared design contract that themes implement and modules build against. Modules use semantic design tokens and pattern specs instead of theme-specific CSS, so their UI looks and behaves consistently under any theme that implements the contract, and acceptably under themes that don't, thanks to built-in defaults.

Built on core's Design Tokens API (W3C DTCG format) and Single Directory Components. Framework-agnostic: works for Twig, vanilla JS and islands in any framework.

Includes:
- the contract vocabulary of semantic tokens, with default values for admin and frontend contexts
- structured design rules (must / should / may) with stable IDs, readable by people, linters and AI assistants
- a resolver that merges contract, theme and project layers and outputs CSS custom properties
- adapters for the core themes Claro and Default Admin

Status: experimental. The vocabulary will change while it's being developed together with theme maintainers.