Fix extract concurrency issue when disabling cssCodeSplit

Editor assessment

The subject `fix(css): fix extract concurrency issue when disabling cssCodeSplit` names the scope, the defect class — a concurrency issue in extraction — and the exact triggering configuration, with the doubled fix verb the only wart. The fix type and css scope are accurate. No body or footer appears, acceptable because the subject fully specifies the failure mode and its condition. No junk otherwise. Precise, conditional, and self-sufficient.