Focused-trip data layer: stops-for-route fetched via two paths, shapes double-cached, focusedTrips in three copies

[bmander]

From the 2026-07-16 debt review (finding 8). Severity: medium.

Three related smells introduced by #1865/#1893:

1. stops-for-route via two independent repository paths. FocusedTripRepository.getStops uses RouteStopsDataSource.stopsForRoute with its own routeStopCache (FocusedTripRepository.kt:124-125,190-194), while RouteMapRepository.getRoute hits the same wire endpoint uncached via MapDataSource.routeMap (MapDataSource.kt:72-73), into a different model shape (RouteStopGroup vs RouteMapStop); RouteInfoRepository is a third consumer. "Focus a stop, then select one of its routes" fetches stops-for-route twice with no coalescing, and the two projections can come from different fetches. Refactor: one caching stops-for-route repository both project from. (medium)

2. Shape geometry double-cached under the same shapeId with divergent policies. TripObservationRepository's ShapeCache (Polyline, LRU 100, no TTL) vs FocusedTripRepository.shapeCache (List<GeoPoint>, LRU 32, 10-min TTL — FocusedTripRepository.kt:71-73,126-127,209-219). ~2x memory per focused shape, two eviction policies, and the 10-minute TTL on effectively immutable GTFS data is an unexplained freshness threshold (contrast MAX_CACHED_SHAPES, which carries a full rationale). Drop or document the TTL. (small)

3. The focused-trip set has three copies with scattered manual resets. ArrivalsRepository.lastGood.loaded.focusedTrips (ArrivalsRepository.kt:486-492) → HomeViewModel.focusedTrips, a plain var (HomeViewModel.kt:155) reset imperatively at four sites (175, 363, 471, 545) → RouteMapController.stopFocusSession.trips. Deriving the set from the focus state flow removes the "forgot to clear on transition X" bug class. (medium)

[bmander]

All three findings addressed and merged into main:

1. Stops-for-route unified behind one caching repository — Unify stops-for-route behind one caching repository (#1908) #1921
2. Shape double-cache dropped, reusing shared Polyline cache — Reuse shared Polyline cache for focused shapes; drop decoded double-cache (#1908) #1919
3. focusedTrips now derived from the focus state flow — Derive the focused-trip set from the current focus (#1908) #1922

Closing.