Switching Favorites<->Watchlist (props swap in place, no remount) left the
page blank with only the tab buttons: the empty-state was written as a side
effect inside the queryFn, which React Query skips on cache hits, and a reset
effect then cleared it — so on a cache-served switch nothing repopulated it,
every list was hidden by hideIfEmpty, and the empty message never rendered.
Each list now reports emptiness once its query settles (incl. cache hits) via
a new optional onEmptyStateChange callback on InfiniteScrollingCollectionList
(mobile + TV), reporting null while loading so a switch never flashes a stale
state. The parent derives the aggregate empty-state from that (null = not
settled yet, so the message stays hidden during a switch).
The reset effect is removed entirely, not kept: React runs child effects
before parent effects within a commit, so a parent reset setEmptyState(false)
would clobber the children's reported values on the same render. Dropping it
and using the per-list callbacks (tri-state null/true/false) is what makes the
switch — including a cache-served one — resolve to the correct state. Applies
to both mobile and TV Favorites.
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