[joshblack]

Enable React Compiler for useSafeTimeout, the private token remove button, and UnderlinePanels. This combines the small migrations from #8553, #8554, and this PR into one review without changing their implementation.

Our migration report identifies the cleanup ref access, ref handling through remaining props, and captured positional counters as the respective blockers.

Changelog

New

Changed

• Capture the timer Set when the useSafeTimeout effect runs. Cleanup retains the same mutable Set, including timers registered after the effect.
• Remove unused explicit ref handling from the private token remove button.
• Keep UnderlinePanels' positional counters in a local object, preserving explicit values, independent tab and panel indexing, child order, and slot matching.
• Remove the three compiler exclusions and add minor changesets, matching our recent compiler rollout.

Removed

Rollout strategy

• No changes needed in github/github-ui
• Needs changes in github/github-ui
• Ships with feature flag(s)
• Not sure
• None

[changeset-bot]

🦋 Changeset detected

Latest commit: 4fa9b73

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. Check the integration testing docs for step-by-step instructions. Or, apply the integration-tests: skipped manually label to skip these checks.

[primer-integration]

Integration test results from github/github-ui PR:

  Changes Waiting
  CI Passed
  VRT Running
  Projects Passed

[Copilot]

🟢 Approval recommended

Static review found no blocking issues in these focused compatibility refactors; tests and compilation were not run.

No open issues 🎉

What changed in this PR

Enables React Compiler for useSafeTimeout, private token remove buttons, and experimental UnderlinePanels.

Changes:

• Refactors timer cleanup, unused ref handling, and positional counters for compiler compatibility.
• Removes compiler exclusions for all three implementations.
• Adds minor changesets documenting the rollout.

File	Description
packages/​react/​src/​Token/​_RemoveTokenButton.tsx	Removes unused explicit ref handling.
packages/​react/​src/​hooks/​useSafeTimeout.ts	Captures the shared timer Set for cleanup.
packages/​react/​src/​experimental/​UnderlinePanels/​UnderlinePanels.tsx	Groups positional counters in a local object.
packages/​react/​script/​react-compiler.mjs	Removes three compiler exclusions.
.changeset/​react-compiler-underline-panels.md	Documents UnderlinePanels compiler support.
.changeset/​react-compiler-token-remove-button.md	Documents token rendering improvements.
.changeset/​react-compiler-safe-timeout.md	Documents timeout hook compiler support.

_{Review effort: Balanced}