The defect
no scanner reports

On screens up to 380 px wide - common Android models - the contact block was wider than the page: the document stretched to 370 px against a 360 px screen. The right border of the cards and the edge of the section heading fell outside the visible area.

Why it went unnoticed

The defect hid behind body { overflow-x: hidden }. That line disables horizontal scrolling - the page does not drift sideways, so everything looks fine. The extra pixels are simply never shown. The symptom is not that something moved; it is that part of the content silently fails to render.

It cannot be reproduced on an iPhone (390 px and wider) - everything fits there. Checking "I opened it on my phone, looks fine" cannot catch this class of defect at all.

What automated checks say

Nothing. HTML and CSS are valid, zero console errors, no failed requests, Lighthouse is happy. Linters and scanners stay quiet because the code is syntactically correct - only the behaviour at a specific screen width is wrong.

Root cause

The classic flexbox trap: items inside a row default to min-width: auto and refuse to shrink below their content. The label on the left was pinned at 5.5rem while the long email on the right could not compress - together they stopped fitting the container.

The fix

Five lines of CSS: on narrow screens the row wraps, the label takes its own line above the value, and the value is allowed to shrink.

@media (max-width: 520px) {
  .row    { flex-wrap: wrap; row-gap: 0.35rem; }
  .rowLbl { min-width: 0; flex: 0 0 100%; }
  .rowVal { min-width: 0; overflow-wrap: anywhere; }
}

Verification

The measurement was repeated at four widths on the live site after deployment. The criterion: document width never exceeds screen width, and no text sits beyond the edge.

320 px → 320 / 320 · clipped text: 0 · OK
360 px → 360 / 360 · clipped text: 0 · OK
390 px → 390 / 390 · clipped text: 0 · OK
414 px → 414 / 414 · clipped text: 0 · OK

"It builds without errors" is not proof. Proof is that the defect stopped reproducing where it used to reproduce.