Two unrelated things landed together.
The first is the day model. A spaced-repetition app has to decide when “today” is, and midnight isn’t always the right answer. ADR-0018 pins the study day to 04:00, so a learner who reviews at 01:30 is still on the previous day’s schedule, with a grace window for travel and a clamp so a clock change can’t push a streak backwards.
The second is share cards: three outbound share cards so a learner can tell someone what they’re studying. Small, but it’s the kind of feature that has to render correctly on device, and the day-model work had already forced the clock handling to be honest, which the share feature inherited for free.