(WIP) RFC: Bring the CAP visual language into Fluent UI v9

[GianoglioEnrico]

Overview

Proposes making the CAP visual language a first-class part of Fluent UI v9: consumers opt in via @fluentui/react-components alone (no @fluentui-contrib/* dependency), CAP source lives in the Fluent monorepo, and CAP is discoverable on the docs site as a visual-language picker alongside the theme picker.

Implementation tracked in #36308 .

What's in this RFC

A phased move of CAP_STYLE_HOOKS from fluentui-contrib into Fluent v9:

• Phase 1 — re-export. @fluentui/react-components adds the contrib package as an internal dependency and re-exports CAP_STYLE_HOOKS from the main barrel. Consumers drop @fluentui-contrib/* from package.json and write import { CAP_STYLE_HOOKS } from '@fluentui/react-components'.
• Phase 2 — move source. A new packages/react-components/react-cap-theme/ package owns CAP inside the monorepo, on Fluent's release cadence, gated by Fluent's CI (bundle size, VR, conformance). Contrib becomes a deprecated re-export shim.

What I'm asking reviewers to decide

The RFC closes with the following open questions:

• Skip Phase 1 entirely? Collapse Phase 1+2 into a single @fluentui/react-cap-theme-preview move?
• Distribution shape — confirm main-barrel re-export over subpath or separate preview package.
• Docs-site toggle UX — does docs-site en

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