[Prajwal-4121998]

…, dark theme fix, nav safety guards, bundled fonts
core:designsystem Polish — 2026 Production Loading UX
Summary

Upgrades loading states across Catalog, Detail, and the design system to content-shaped skeleton screens, a unified Coil image pipeline, and crossfade-based state transitions — replacing spinner-based loading with the pattern used by production catalog/e-commerce apps. Also fixes several real bugs surfaced during implementation: a silent no-op refresh, a dead retry button, a dark-mode theming bug affecting every screen, and double-tap navigation crashes.

What's included

Skeleton loading system

ProductCardSkeleton, SearchResultSkeleton, DetailSkeleton, CategoryChipRowSkeleton — content-shaped shimmer skeletons structurally locked to their real counterparts via shared *Defaults objects (ProductCardDefaults, SearchResultCardDefaults, DetailBottomBarDefaults) promoted to core:designsystem, eliminating drift risk between loading and loaded states
AnimatedContent-driven crossfades (Loading/Error/Empty/Content) on Catalog and Detail, keyed on enum-based contentState() derived state instead of raw booleans

Image pipeline

CatalogAsyncImage — unified Coil wrapper with theme-aware tonal placeholder and a distinct error state (muted broken-image icon over the same tonal background), replacing raw AsyncImage calls across feature:catalog, feature:detail, feature:search
Non-success visuals grouped into CatalogImagePlaceholders to keep the composable's parameter count under Detekt's LongParameterList threshold

Navigation

NavHost enter/exit/pop transitions with FastOutSlowInEasing
navigateSafely() / popBackStackSafely() extensions on NavController, gating navigation on back-stack entry RESUMED state — prevents duplicate navigation from rapid double-taps or multiple simultaneous triggers (two product cards tapped in quick succession, back button double-tapped)
Root Surface background added around NavHost to eliminate a white flash during slide transitions (window background gap)

Bug fixes found during implementation

CatalogViewModel.refreshProducts() was a no-op (set isRefreshing = true then immediately false with no actual fetch) — replaced with shared fetchProducts(showAsRefresh: Boolean), verified via verify(exactly = 2) { getProductsUseCase() } (previous test passed against the broken version — replaced, not just patched)
DetailViewModel had no RetryLoad intent — retry button on the error state did nothing; added intent + currentProductId tracking
DarkColorScheme had surfaceContainerLow/surfaceContainerLowest/surfaceContainerHigh wired to their light-mode color values instead of the *Dark variants — root cause of every screen (top bar, cards, bottom bar, chips) showing white/light backgrounds in dark mode despite correct dark values already being defined and unused

Other
Detekt fixes: CatalogAsyncImage parameter grouping (LongParameterList), DetailSkeleton split into sub-composables (LongMethod)
Testing
CatalogViewModelTest: replaced weak refresh test with call-count verification + a test asserting a failed refresh doesn't wipe existing products
Manual on-device pass: skeleton→content crossfades (light/dark), pull-to-refresh, rapid-tap navigation guard, retry flow, dark mode across all screens, image placeholder/error states under throttled network
Deferred (tracked, not lost)
App cold-start investigation (~7s gap on Android 13-and-below emulator, ViewModel init → first render) — narrowed to likely debug-build classloading cost; pending release-build/real-device timing confirmation. Baseline Profiles identified as the fix if confirmed.
Nav transition perceived lag — deferred to a dedicated Profiler session (Find CPU Hotspots)
Search screen loading skeleton — scoped out; existing debounce/typing rhythm judged sufficient
Detail bottom bar skeleton — implemented then reverted (low-dwell UI, snap is imperceptible; simplified via AnimatedVisibility reasoning, then dropped by scope decision)
lastUpdated staleness timestamp — implemented then removed; doesn't serve FakeStore's static data, reserved for WorkManager sync feedback later
Checklist
[] lintDevDebug passing
[]detekt passing
[]testDevDebugUnitTest passing
[]jacocoTestReport / jacocoTestCoverageVerification passing
[]assembleDevDebug passing
[]Manual verification on emulator (light + dark mode)