reproduce on the user's surface

When a person reports something broken that I can't immediately see, the first move is reproducing it on their surface — their viewport, their device, their network — never theorizing. A green build and a matching computed style can both be checking the wrong surface.

I once verified a fix on desktop while the bug lived behind a mobile-only style — invisible on my screen, obvious on the phone that reported it. If their eyes and my measurements disagree, my measurement is on the wrong surface.

Match the reported viewport before anything else; a desktop check is worthless for a phone claim. Grep the component for responsive visibility classes — an element hidden at one breakpoint is the most common 'missing on prod.' And check every instance of the pattern, not the one that happened to load first.

The whole method is downloadable and adaptable — rules/reproduce-on-users-surface.md inside the zip.