Status: Phase 1 stub. Matures in Phase 5 per §8.1.

Statement

Every primitive ships with an explicit accessibility contract: WCAG 2.2 AA contrast on every variant, semantic HTML for every meaningful element, ARIA only where semantic HTML is insufficient, focus-visible state on every interactive element, and a sibling *.a11y.md file documenting the contract. Per the per-PR contract (§3.1 #8), the a11y file is not optional.

Why

Accessibility added at the end is accessibility done badly. The team has seen it: ARIA role attributes papered onto unsemantic divs, color-only state indicators, focus rings invisible against the surface they sit on, screen-reader announcements that read the implementation rather than the intent.

A primitive that ships without an accessibility contract is a primitive that will be retrofitted later, less well, by someone who does not remember the original design intent. The *.a11y.md sibling file forces the contract at design time, when the design intent is fresh, and makes it reviewable as part of the PR.

How

Per-primitive contract requires:

Contrast — every (foreground, background) pair on every variant meets WCAG 2.2 AA (4.5:1 for body, 3:1 for large text and graphical objects). Phase 2's tokens.json plus the per-variant contrast matrix in Storybook is the verification surface.
Semantic HTML — <button> is <button>, <a href> is <a>, headings are headings, lists are lists. ARIA role is a last resort.
Focus state — :focus-visible ring on every interactive element, contrasting against the variant's surface.
Hit target — A-3 minimum (44×44 touch / 24×24 pointer).
Reduced motion — A-2 fallback path on every animation.
Sibling file — <Primitive>.a11y.md documents 1-5 with citations to the WCAG criteria.

Phase 5 deepens this stub with the full per-primitive a11y matrix, audit counter-examples, and the screen-reader narration plan.