Check Backend Health When the App Returns to the Foreground

[TheZupZup]

Overview

Context: Once the Flutter app connects to the backend on startup, it assumes the connection stays alive forever. There is no check when the user switches away from the app and returns. If the Python backend was restarted or the machine went to sleep in the meantime, the next API call fails unexpectedly.

This issue adds a lightweight health check whenever the app resumes from background.

What needs to be done

• In HomeScreen (or main.dart), add a WidgetsBindingObserver and override didChangeAppLifecycleState()
• When AppLifecycleState.resumed is triggered, call AppState.checkBackendHealth() (to be added as part of Trigger a Sync Automatically When the App Reconnects to the Backend #23, or add it here first as a simple ping() call)
• If the ping succeeds and notes haven't been refreshed in over 30 seconds, call AppState.loadNotes() to pull fresh data
• If the ping fails, set the backend as unreachable and show the offline banner from Show a Banner in HomeScreen When the Backend Is Unreachable #26 (or just log it for now if Show a Banner in HomeScreen When the Backend Is Unreachable #26 isn't done yet)

Goal

When the user comes back to the app after switching away, the app silently checks that the backend is still running and refreshes the notes list if needed — so the user always sees current data.

Where to look

• app/lib/screens/home_screen.dart — add WidgetsBindingObserver here
• app/lib/services/app_state.dart — loadNotes(), add _lastRefreshed timestamp
• app/lib/services/api_client.dart — ping() method

Implementation hint

class _HomeScreenState extends State<HomeScreen> with WidgetsBindingObserver {
  @override
  void initState() {
    super.initState();
    WidgetsBinding.instance.addObserver(this);
  }

  @override
  void dispose() {
    WidgetsBinding.instance.removeObserver(this);
    super.dispose();
  }

  @override
  void didChangeAppLifecycleState(AppLifecycleState state) {
    if (state == AppLifecycleState.resumed) {
      // run health check + optional refresh
    }
  }
}

Testing steps

• Open the app, switch to another app, kill the Python backend, return to the app — verify the offline banner appears (or a snackbar) within a few seconds
• Open the app, switch away, return without killing the backend — verify notes refresh silently with no visible disruption

Notes

This is a good first issue. It's a small, self-contained change in home_screen.dart that uses a standard Flutter lifecycle API. The full offline/reconnect logic is tracked in #22 and #23.

Related to: #22, #23, #26