Assert text wrapping directly in responsive visual tests

A responsive test that checks only visibility and horizontal overflow can still miss unwanted multi-line labels. When compact form controls must remain single-line, measure the rendered label height against its computed line height at each supported viewport, and pair that assertion with deliberate grid track sizing plus white-space: nowrap. This applies to short, product-required labels where sufficient width is reserved; it should not be used to force long or localized copy into overflow.

Evidence/example — 2026-09-10, Shield COR-4129 / PR #829: an optional pickup-time label wrapped inside a nested equal-width grid even though the dialog had no horizontal overflow. Widening the combined date/time track and adding a geometry assertion across eight viewports caught the exact regression. Source provenance: user-supplied screenshot, repository component, and Playwright fixture.