Architectural improvements: targeted rebuilds, single city source of truth, SQLite WAL + indexes, readiness() lock fix

[Copilot]

Full-stack audit addressing rebuild inefficiency in Flutter, duplicated data across layers, and SQLite performance bottlenecks in the Python backend.

Flutter — widget rebuild reduction

Before: HomeShell.build() was wrapped in AnimatedBuilder(animation: store), recreating all 4 page widget objects on every notifyListeners() call — forcing Flutter to diff and potentially re-render the entire IndexedStack subtree.

After: Pages created once in initState(); each screen subscribes to the store independently via ListenableBuilder:

// home_shell.dart — pages stable across store changes
@override
void initState() {
  super.initState();
  _pages = [
    MapScreen(store: widget.store),
    NewsScreen(store: widget.store),
    RouteScreen(store: widget.store),
    SourcesScreen(store: widget.store),
  ];
}

Per-screen subscription strategy:

• _BlurAppBar, MapScreen, NewsScreen: full build() wrapped in ListenableBuilder
• RouteScreen: only risk-result card wrapped — evaluate button (_isEvaluating) stays driven by setState
• SourcesScreen: targeted wrappers on error message and source diagnostics; form fields unchanged

NewsScreen converted to StatefulWidget to cache DateFormat in initState() rather than re-instantiating on every build.

Flutter — single source of truth for city data

Removed two parallel city registries:

• AppStore._supportedIndianCities — 27-entry Set<String>
• _SourcesScreenState._indianCityCenters — 25-entry coordinate Map

Replaced by kCityCoordinates in models.dart, used for validation in AppStore.updateArea(), dropdown population, and coordinate auto-fill in SourcesScreen. Backward-compatible aliases ('New Delhi', 'Bangalore') included.

Python backend — SQLite performance

• WAL mode: PRAGMA journal_mode=WAL in _init_schema() — concurrent reads no longer block on writes
• Spatial indexes: (lat, lng) compound indexes on events_active, risk_cells, and events_log; city index on events_active — eliminates full table scans on the hot-path bounding-box BETWEEN queries
• readiness() double lock: COUNT(*) FROM risk_cells was delegated to count_risk_cells(), acquiring self._lock a second time after readiness() had already released it. Query is now inlined within the existing lock block.

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[Copilot]

Pull request overview

This PR updates the Flutter unit test suite to align GeoArea.center usage with the latlong2 LatLng type, consistent with the current GeoArea model.

Changes:

• Update GeoArea test setup to use LatLng(...) directly instead of a removed/unused LatLngCoordinate(...).toLatLng() conversion.

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[fallofpheonix]

@copilot apply changes based on this feedback

[fallofpheonix]

@copilot apply changes based on this feedback

[fallofpheonix]

@copilot apply changes based on this feedback

[Copilot]

All changes described in the PR title/description are now implemented in commit 924dbcd. That commit contains every item from the plan: single city source of truth (kCityCoordinates), targeted ListenableBuilder rebuild scoping across all screens, HomeShell page list stabilised in initState, DateFormat caching in NewsScreen, WAL mode, spatial indexes on events_active/risk_cells/events_log, and the readiness() double-lock fix. The PR description and title now accurately reflect the full changeset.

[fallofpheonix]

@copilot apply changes based on the comments in this thread

[fallofpheonix]

@copilot apply changes based on the comments in this thread