New rows no longer accept 4_5 (the builder does not offer it). On update, the flexType of every non-desktop breakpoint (tablet, phone, …) is format-checked against the builder list like desktop. Guide updated. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01At3V6SjwbMe6eMzVGW3Hs7