My landing page passed every CI check and was still broken on my customer's phone

Short summary

Author's landing page passed CI checks but rendered broken on real devices (clipped text, contrast failures, broken images). Traditional tools like Lighthouse and unit tests verify behavior, not visual appearance across device viewports. Solution: render on actual device profiles, run deterministic checks (CSS overflow, WCAG contrast), then use vision models for layout-only verification.

• •CI/unit tests verify code behavior but miss viewport-specific rendering bugs
• •Deterministic checks (scrollWidth > clientWidth, contrast ratios) catch measurable issues reliably
• •Vision models should verify layout only after eliminating math-provable problems

Generated with AI, which can make mistakes.