Four per-pixel passes over char masks ran on the pre-scan's critical path on one thread; each pixel's result depends on that pixel alone, so splitting them changes nothing. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01D1G8gJVAy6gp1K5Dz3NE5C