fix(focus-scope): defer MutationObserver focus recovery to prevent hijacking during Tab transitions

[ralphholzmann]

Summary

Fixes a bug where focus is incorrectly hijacked to the FocusScope container during normal Tab key navigation when a React re-render coincides with the focus transition.

Root cause: When tabbing away from an input that triggers a state update on blur (e.g., react-hook-form validation), React's commit phase can remove and re-add DOM nodes via commitMutationEffects → commitDeletions. This fires the MutationObserver callback in handleMutations while document.activeElement is temporarily document.body — the browser is mid-transition between the old focused element and the next tabbable target. The synchronous focus(container) call intercepts this transition and moves focus to the FocusScope container (tabIndex: -1) instead of letting the browser complete the Tab to the next element.

Fix: Defer the document.activeElement === document.body check to requestAnimationFrame. This allows the browser to complete the focus transition first:

• If activeElement has moved to the next tabbable element → no-op (correct behavior)
• If activeElement is still document.body → the focused element was genuinely removed, so we correctly recover by focusing the container

Reproduction

1. Open a Radix Dialog with trapped focus scope
2. Add a form input that triggers a React re-render on blur (e.g., react-hook-form with onBlur validation or onChange in a blur handler)
3. Tab through the form — when leaving the input, focus jumps to the dialog container div instead of the next tabbable element

Test plan

• Tab forward through all elements in a trapped FocusScope — focus should move sequentially without jumping to the container
• Tab forward through elements where an onBlur handler triggers a React re-render — focus should still move to the next element
• Shift+Tab backward through all elements — same behavior
• When a focused element is genuinely removed from the DOM (not a re-render), focus should still recover to the container
• Focus trapping still works: clicking outside the scope should pull focus back
• Loop behavior still works: tabbing past the last element wraps to the first (when loop={true})

🤖 Generated with Claude Code

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