Biggest opportunity
Four onboarding mechanisms compete for the same five seconds, and the tour intermittently eats the first click
A brand-new visitor sees an auto-starting spotlight tour, a "TRY THIS" card in the empty inbox, an empty-week prompt with three calls to action, and a dismissible save banner, all at once, in the first five seconds. Across two live sessions the spotlighted button and quick-add input repeatedly ignored the first trusted click or keystroke and accepted the second.
The pile-up itself (§6.1) was observed directly and is unambiguous; the click-swallowing sub-finding (§6.2) was reproduced repeatedly but the source audit flags it [verify by hand] pending reproduction on real hardware with a different pointing device.

