Two faults in the first cut.
cacheBuffer was height * 2, and height is -1 until the first layout
pass, so ListView refused it outright and said so on every open. Clamped
at zero.
The strip was vertical. TASK-14 asks for "horizontally swiped live app
cards" and the reference shell's carousel says the same thing in its own
comment — the whole strip slides in horizontally. On a phone the thumb
travels sideways, and a vertical list fights the flick-up that dismisses
a card, so the two gestures were competing for the same axis. Horizontal
with snap-one-item, cards filling the viewport.