Decouple @primer/react ThemeProvider from legacy color-scheme merging while preserving @primer/styled-react

[Copilot]

Changelog

@primer/react no longer resolves legacy color schemes in its ThemeProvider path and no longer exports theme.colorSchemes, removing the heavy legacy-theme object from main runtime/export paths. Legacy color-scheme resolution remains intact in @primer/styled-react.

New

• @primer/react now exposes a legacy subpath export for styled-react compatibility:
  • @primer/react/legacy-theme/ts/color-schemes

Changed

• @primer/react ThemeProvider runtime path

  • Removed applyColorScheme + deepmerge usage from packages/react/src/ThemeProvider.tsx
  • Context now provides the plain theme object (no color-scheme deep merge)
  • resolvedColorMode, colorScheme, mode/scheme setters, contextOnly, and data-* attributes remain unchanged

• @primer/react theme export shape

  • Removed colorSchemes from packages/react/src/theme.ts
  • Main theme export no longer pulls in legacy-theme/ts/color-schemes

• @primer/styled-react compatibility path

  • ThemeProvider now imports legacy colorSchemes directly and reconstructs default theme for legacy resolution behavior:

  import {theme as defaultTheme} from '@primer/react'
  import {colorSchemes} from '@primer/react/legacy-theme/ts/color-schemes'
  
  const defaultThemeWithColorSchemes = {...defaultTheme, colorSchemes}

Removed

• From @primer/react ThemeProvider/useTheme path:
  • resolvedColorScheme in ThemeContext shape
  • useTheme().resolvedColorScheme behavior/docs/tests
  • legacy color-scheme fallback/error path in main ThemeProvider

Rollout strategy

• Patch release
• Minor release
• Major release; if selected, include a written rollout or migration plan
• None; if selected, include a brief description as to why

Migration plan (draft PR):

1. Land as breaking (major) with explicit release-note callouts:
   • useTheme().resolvedColorScheme removed from @primer/react
   • theme.colorSchemes removed from @primer/react default theme export
2. Coordinate timing with consumers that still read legacy theme fields directly.
3. For legacy JS-theme resolution needs, consume via @primer/styled-react (which continues to resolve color schemes) or import the legacy subpath explicitly.

Testing & Reviewing

• Focus review on API-surface and ownership boundaries:
  • packages/react/src/ThemeProvider.tsx
  • packages/react/src/theme.ts
  • packages/styled-react/src/components/ThemeProvider.tsx
• Verify that @primer/react no longer carries legacy color-scheme resolution in ThemeProvider context while @primer/styled-react behavior remains unchanged for existing tests/consumers.

[changeset-bot]

🦋 Changeset detected

Latest commit: 50b90b5

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
@primer/react	Major
@primer/mcp	Patch

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