On a short viewport the seed-confirmation tickbox sits below the fold inside
the step's scrolling area while Continue stays pinned and disabled in the
fixed footer — onboarding reads as broken rather than incomplete.
The cue is a sticky-bottom scrim and glass pill inside the scroll region, and
its visibility comes from real geometry: scrollHeight vs clientHeight for
overflow, then a getBoundingClientRect comparison of the tickbox's bottom
against the container's. On a tall screen the element does not render at all,
so those screens are unchanged. Rects rather than offsetTop because offsetTop
is relative to the nearest positioned ancestor — here the outer card, not the
scroll container.
It is wayfinding only: activating it scrolls the tickbox into view and never
sets confirmed, focuses Continue, or auto-ticks, which a test pins.
Listener setup was moved onto both onMounted paths — the sessionStorage
restore path returned early, so a user navigating back would have had no cue.
Verified: 6 new tests plus the full frontend suite green.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
