bug(react): useAskableFocusSource crashes during SSR #366

Summary

useAskableFocusSource() reads document.activeElement inside its useState initializer, so rendering a component that uses this hook on the server throws ReferenceError: document is not defined.

Evidence

packages/react/src/useAskableFocusSource.ts initializes state with direct document access around lines 39–46. The normal React adapter has SSR tests, but this newer source hook is not covered by them.

Reproduced against main at 40a3374 after a full build:

ReferenceError: document is not defined

The reproduction renders a component using useAskableFocusSource() with react-dom/server.

Proposed fix

• Return a browser-neutral initial snapshot when typeof document === 'undefined'.
• Read the real active element only in a browser-safe path.
• Guard the effect as additional defense.
• Clear the deferred focusout timer during cleanup so it cannot update after unmount.

Acceptance criteria

• renderToString() succeeds for a component using useAskableFocusSource()
• SSR snapshot reports no focused element
• Browser hydration still initializes/tracks the actual focused element correctly
• Pending focusout work is cancelled on unmount
• Existing React tests continue to pass