graduate primer_react_theme_provider_remove_ssr_handoff ff

[francinelucca]

Changelog

Removed

• primer_react_theme_provider_remove_ssr_handoff and related code

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

Testing & Reviewing

Merge checklist

• Added/updated tests
• Added/updated documentation
• Added/updated previews (Storybook)
• Changes are SSR compatible
• Tested in Chrome
• Tested in Firefox
• Tested in Safari
• Tested in Edge
• (GitHub staff only) Integration tests pass at github/github-ui (Learn more about how to run integration tests)

[changeset-bot]

🦋 Changeset detected

Latest commit: fda08a3

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

This PR includes changesets to release 1 package

Name	Type
@primer/react	Minor

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[github-actions]

⚠️ Action required

👋 Hi, this pull request contains changes to the source code that github/github-ui depends on. If you are GitHub staff, test these changes with github/github-ui using the integration workflow. If this doesn't work, you can also use the original workflow here. Check the integration testing docs for step-by-step instructions. Or, apply the integration-tests: skipped manually label to skip these checks.

To publish a canary release for integration testing, apply the Canary Release label to this PR.

[Copilot]

Pull request overview

Removes the primer_react_theme_provider_remove_ssr_handoff feature flag and associated SSR handoff/script logic from ThemeProvider, simplifying how resolvedColorMode is determined and making preventSSRMismatch a deprecated no-op.

Changes:

• Removed SSR handoff cache + <script type="application/json"> injection and feature-flag gating from ThemeProvider.
• Deprecated preventSSRMismatch (now has no effect) and removed related unit tests.
• Removed the graduated feature flag from DefaultFeatureFlags.

Show a summary per file

File	Description
packages/react/src/ThemeProvider.tsx	Removes SSR handoff/script logic and feature-flag checks; deprecates preventSSRMismatch as a no-op.
packages/react/src/FeatureFlags/DefaultFeatureFlags.ts	Deletes the graduated primer_react_theme_provider_remove_ssr_handoff default flag entry.
packages/react/src/tests/ThemeProvider.test.tsx	Removes tests and imports related to SSR handoff/script rendering and the feature flag.

Copilot's findings

• Files reviewed: 3/3 changed files
• Comments generated: 2

[primer-integration]

Integration test results from github/github-ui PR:

  CI Waiting
  VRT Passed
  Projects Waiting