ROOT CAUSE: @State TripsViewModel inside TripsHomeView was recreated
during navigation transitions. Each recreation set isLoading=true,
flipping the Group conditional, destroying the ScrollView + namespace.
The zoom transition's matchedTransitionSource evaporated.
FIXES (matching Apple's Wishlist pattern):
1. ViewModel owned by MainTabView (like ReaderVM) — survives
view recreation. Pre-loaded on app launch.
2. Loading state rendered INSIDE ScrollView — no conditional
Group wrapper that swaps the entire view tree.
3. Single @Namespace in TripsHomeView, passed to both
UpcomingTripsPageView and PastTripsSection.
4. Zoom transition restored on all NavigationLinks.
Why Apple's sample works: they use @Environment(DataSource.self)
which is app-level stable. Our equivalent: @State at MainTabView.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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