refactor(main): break the main.dart / router.dart import cycle

router.dart imported main.dart for ProviderInitializer and BeerFestivalHome
while main.dart imported router.dart for appRouter, so main.dart was not an
entry point but a widget library that happened to contain main(), and
neither file could be read or tested without the other.

Move both widgets to lib/widgets/ and export them from the barrel. They are
copied verbatim — the only edit is one comment pointer.

globalRoutes moves from router.dart to utils/navigation_helpers.dart rather
than staying put as the issue suggested: the redirect handler that reads it
now lives under lib/widgets/, and router.dart imports the widgets barrel, so
leaving it in router.dart would simply re-form the cycle one file over.
navigation_helpers.dart has no project imports of its own and already owns
the route-path builders, so it is the natural cycle-free home.

main.dart is now main() + isTransientFontLoadError + BeerFestivalApp, 104
lines instead of 440. Nothing under lib/ imports it any more.

Removing the moved code left six dead imports in main.dart, which the
newly-fatal analyzer from #524 caught immediately.

Follow-up not done here, to keep this a pure move: the BeerFestivalHome and
ProviderInitializer tests still live in test/main_test.dart rather than
mirroring the new lib/widgets/ layout.

Fixes #527

Author: claude

lib/main.dart

@@ -1,18 +1,12 @@
-import 'dart:async';
-import 'dart:ui';
 import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
-import 'package:flutter/services.dart';
 import 'package:firebase_core/firebase_core.dart';
 import 'package:firebase_crashlytics/firebase_crashlytics.dart';
-import 'package:go_router/go_router.dart';
 import 'package:provider/provider.dart';
 import 'app_theme.dart';
 import 'providers/providers.dart';
 import 'router.dart';
 import 'services/services.dart';
-import 'utils/utils.dart';
-import 'widgets/widgets.dart';
 import 'firebase_options.dart';
 // Guarded on dart.library.js_interop, not dart.library.html: `dart:html` is
 // only provided by dart2js, so a `--wasm` build would silently fall through to
@@ -108,333 +102,3 @@ class BeerFestivalApp extends StatelessWidget {
     // coverage:ignore-end
   }
 }
-
-/// Widget that initializes the BeerProvider before rendering children
-/// This ensures provider is initialized for all routes, including deep links
-class ProviderInitializer extends StatefulWidget {
-  final Widget child;
-
-  const ProviderInitializer({super.key, required this.child});
-
-  @override
-  State<ProviderInitializer> createState() => _ProviderInitializerState();
-}
-
-class _ProviderInitializerState extends State<ProviderInitializer>
-    with WidgetsBindingObserver {
-  bool _initialized = false;
-
-  @override
-  void initState() {
-    super.initState();
-    WidgetsBinding.instance.addObserver(this);
-  }
-
-  @override
-  void dispose() {
-    WidgetsBinding.instance.removeObserver(this);
-    super.dispose();
-  }
-
-  @override
-  void didChangeAppLifecycleState(AppLifecycleState state) {
-    super.didChangeAppLifecycleState(state);
-
-    // When app resumes to foreground, refresh data if stale
-    if (state == AppLifecycleState.resumed) {
-      unawaited(context.read<BeerProvider>().refreshIfStale());
-    }
-  }
-
-  @override
-  void didChangeDependencies() {
-    super.didChangeDependencies();
-    if (!_initialized) {
-      _initialized = true;
-      // Initialize and load drinks for all routes. initialize() never throws
-      // (a startup failure surfaces as provider.error), so the redirect below
-      // always runs and the app never strands on the loading screen.
-      final provider = context.read<BeerProvider>();
-      unawaited(
-        provider.initialize().then((_) {
-          unawaited(provider.loadDrinks());
-          // After initialization, trigger redirects that were deferred
-          _handlePostInitRedirect();
-        }),
-      );
-    }
-  }
-
-  /// Handle route redirects after provider initialization
-  ///
-  /// CONTEXT: go_router's redirect callbacks run once on initial navigation and
-  /// don't re-run when provider state changes. This method explicitly handles
-  /// redirects that were deferred during initialization.
-  ///
-  /// KNOWN LIMITATIONS:
-  /// - Deep links with invalid festival IDs in subpaths are NOT redirected
-  ///   Example: /invalid-fest/drink/abc stays at /invalid-fest/drink/abc
-  ///   Reason: These match route patterns directly (/:festivalId/drink/:id)
-  ///           bypassing the festival home redirect logic
-  ///   Impact: User sees 404 or broken state until they navigate away
-  ///   Fix: Requires adding festival ID validation to ALL route builders
-  ///
-  /// - URL fragments are not preserved during redirects
-  ///   Example: /invalid-fest#section → /cbf2025 (loses #section)
-  ///   Impact: Scroll position hints from deep links are lost
-  ///   Fix: Preserve currentUri.fragment in redirect URL construction
-  void _handlePostInitRedirect() {
-    if (!mounted) return;
-
-    try {
-      final router = GoRouter.of(context);
-      final state = GoRouterState.of(context);
-      final provider = context.read<BeerProvider>();
-
-      final currentUri = state.uri;
-      final currentPath = currentUri.path;
-      final segments = currentUri.pathSegments;
-
-      // Check if we're on root path - redirect to festival home
-      if (currentPath == '/') {
-        router.go('/${provider.currentFestival.id}');
-        return;
-      }
-
-      // Global routes (no festival scope) - do NOT redirect these
-      // Uses constant from router.dart to avoid duplication
-      if (globalRoutes.contains(currentPath)) {
-        return; // Stay on global route
-      }
-
-      // For festival-scoped routes, validate the festival ID
-      // Early return: if already on valid festival route, skip expensive checks
-      if (segments.isNotEmpty && provider.isValidFestivalId(segments.first)) {
-        // Sync provider when the URL festival differs from the current one.
-        // This is the primary fix for cold-loading a non-default festival URL
-        // (browser refresh, shared link opened fresh).
-        if (segments.first != provider.currentFestival.id) {
-          final festival = provider.getFestivalById(segments.first);
-          if (festival != null) {
-            unawaited(provider.setFestival(festival, persist: false));
-          }
-        }
-        return;
-      }
-
-      // Path pattern: /:festivalId or /:festivalId/...
-      // Extract first path segment as potential festival ID
-      if (segments.isEmpty) return;
-
-      final firstSegment = segments.first;
-
-      // If first segment is not a valid festival ID, redirect
-      if (!provider.isValidFestivalId(firstSegment)) {
-        // Preserve the rest of the path and query parameters
-        final restOfPath = segments.length > 1
-            ? '/${segments.sublist(1).join('/')}'
-            : '';
-        final queryString = currentUri.query.isNotEmpty
-            ? '?${currentUri.query}'
-            : '';
-        router.go('/${provider.currentFestival.id}$restOfPath$queryString');
-      }
-    } catch (e, stackTrace) {
-      if (kDebugMode) {
-        debugPrint('Post-init redirect error: $e');
-        debugPrint(stackTrace.toString());
-      } else {
-        // coverage:ignore-start
-        // In production, log to crashlytics
-        final provider = context.read<BeerProvider>();
-        unawaited(
-          provider.analyticsService.logError(
-            e,
-            stackTrace,
-            reason: 'Post-initialization redirect failed',
-          ),
-        );
-        // coverage:ignore-end
-      }
-    }
-  }
-
-  @override
-  Widget build(BuildContext context) {
-    final provider = context.watch<BeerProvider>();
-
-    // Show loading screen until provider is initialized
-    if (provider.isLoading && provider.allDrinks.isEmpty) {
-      return const Scaffold(
-        body: Center(
-          child: Column(
-            mainAxisAlignment: MainAxisAlignment.center,
-            children: [
-              CircularProgressIndicator(),
-              SizedBox(height: 16),
-              Text('Loading festival data...'),
-            ],
-          ),
-        ),
-      );
-    }
-
-    return widget.child;
-  }
-}
-
-class BeerFestivalHome extends StatefulWidget {
-  final Widget child;
-
-  const BeerFestivalHome({super.key, required this.child});
-
-  @override
-  State<BeerFestivalHome> createState() => _BeerFestivalHomeState();
-}
-
-const Duration _exitConfirmationWindow = Duration(seconds: 2);
-const String _exitConfirmationMessage = 'Press back again to exit';
-
-class _BeerFestivalHomeState extends State<BeerFestivalHome> {
-  Timer? _exitConfirmationTimer;
-
-  int get _currentIndex {
-    // Try to get the current location from GoRouter
-    try {
-      final location = GoRouterState.of(context).uri.toString();
-      if (location.endsWith('/favorites')) return 1;
-      return 0;
-    } catch (e) {
-      // If GoRouter is not available (e.g., in tests), default to 0
-      return 0;
-    }
-  }
-
-  /// Get festivalId from current route
-  String? get _festivalId {
-    try {
-      final params = GoRouterState.of(context).pathParameters;
-      return params['festivalId'];
-    } catch (e) {
-      return null;
-    }
-  }
-
-  void _onDestinationSelected(int index) {
-    // Try to use GoRouter navigation
-    try {
-      // Get festival ID from URL or fall back to provider
-      final festivalId =
-          _festivalId ?? context.read<BeerProvider>().currentFestival.id;
-
-      if (index == 0) {
-        context.go(buildFestivalHome(festivalId));
-      } else if (index == 1) {
-        context.go(buildFavoritesPath(festivalId));
-      }
-    } catch (e) {
-      // If GoRouter is not available, this is a no-op
-      // (tests that don't use GoRouter won't navigate)
-    }
-  }
-
-  @override
-  void dispose() {
-    _exitConfirmationTimer?.cancel();
-    super.dispose();
-  }
-
-  void _handleExitConfirmation() {
-    if (!mounted) return;
-
-    if (_exitConfirmationTimer?.isActive ?? false) {
-      _exitConfirmationTimer!.cancel();
-      _exitConfirmationTimer = null;
-      if (!kIsWeb) {
-        SystemNavigator.pop();
-      }
-      return;
-    }
-
-    _exitConfirmationTimer = Timer(_exitConfirmationWindow, () {
-      _exitConfirmationTimer = null;
-    });
-
-    ScaffoldMessenger.of(context)
-      ..hideCurrentSnackBar()
-      ..showSnackBar(
-        const SnackBar(
-          content: Text(_exitConfirmationMessage),
-          duration: _exitConfirmationWindow,
-        ),
-      );
-  }
-
-  @override
-  Widget build(BuildContext context) {
-    final hasNavigationHistory = canPopNavigation(context);
-
-    return PopScope(
-      canPop: kIsWeb || hasNavigationHistory,
-      onPopInvokedWithResult: (didPop, result) {
-        final canPopNow = canPopNavigation(context);
-        if (didPop || canPopNow) {
-          _exitConfirmationTimer?.cancel();
-          _exitConfirmationTimer = null;
-          return;
-        }
-        _handleExitConfirmation();
-      },
-      child: Scaffold(
-        body: Stack(children: [widget.child, const EnvironmentBadge()]),
-        bottomNavigationBar: NavigationBar(
-          height: 60,
-          labelBehavior: NavigationDestinationLabelBehavior.alwaysHide,
-          selectedIndex: _currentIndex,
-          onDestinationSelected: _onDestinationSelected,
-          destinations: [
-            NavigationDestination(
-              key: const Key('drinks_tab'),
-              icon: Semantics(
-                label: 'Drinks tab, browse all festival drinks',
-                child: Opacity(
-                  opacity: 0.6,
-                  child: Image.asset(
-                    'assets/app_icon.png',
-                    width: 24,
-                    height: 24,
-                  ),
-                ),
-              ),
-              selectedIcon: Semantics(
-                label: 'Drinks tab, browse all festival drinks',
-                child: Image.asset(
-                  'assets/app_icon.png',
-                  width: 24,
-                  height: 24,
-                ),
-              ),
-              label: 'Drinks',
-            ),
-            NavigationDestination(
-              key: const Key('favorites_tab'),
-              icon: Semantics(
-                label:
-                    'My Festival tab, view your want-to-try list and'
-                    ' tasting log',
-                child: const Icon(Icons.bookmark_outline),
-              ),
-              selectedIcon: Semantics(
-                label:
-                    'My Festival tab, view your want-to-try list and'
-                    ' tasting log',
-                child: const Icon(Icons.bookmark),
-              ),
-              label: 'My Festival',
-            ),
-          ],
-        ),
-      ),
-    );
-  }
-}

lib/router.dart

@@ -6,11 +6,7 @@ import 'package:go_router/go_router.dart';
 import 'package:provider/provider.dart';
 import 'providers/beer_provider.dart';
 import 'screens/screens.dart';
-import 'main.dart';
-
-/// Global routes that exist outside festival scope
-/// IMPORTANT: Keep in sync with _handlePostInitRedirect in main.dart
-const List<String> globalRoutes = ['/about'];
+import 'widgets/widgets.dart';
 
 /// Rebuilds [state]'s location with the leading festival segment replaced by
 /// [currentFestivalId], preserving everything else about the URL.
@@ -120,8 +116,8 @@ GoRouter _buildRouter() {
             // it mounts a Navigator with an empty `pages` list and no
             // `onGenerateRoute`, which crashes with "Null check operator used
             // on a null value" in release builds (issue #386). Once
-            // initialization completes, _handlePostInitRedirect in main.dart
-            // navigates to the current festival.
+            // initialization completes, _handlePostInitRedirect in
+            // widgets/provider_initializer.dart navigates to the current festival.
             builder: (context, state) => const Scaffold(
               body: Center(child: CircularProgressIndicator()),
             ),

lib/utils/navigation_helpers.dart

@@ -10,6 +10,16 @@ library;
 import 'package:flutter/material.dart';
 import 'package:go_router/go_router.dart';
 
+/// Routes that exist outside festival scope and must never be rewritten to a
+/// festival-scoped path.
+///
+/// IMPORTANT: keep in sync with the route table in `router.dart` and with
+/// `_handlePostInitRedirect` in `widgets/provider_initializer.dart` — both
+/// consume this list. It lives here, alongside the path builders, rather than
+/// in `router.dart` so that the redirect handler can read it without importing
+/// the router (which would reintroduce the import cycle removed in #527).
+const List<String> globalRoutes = ['/about'];
+
 /// Builds a festival-scoped URL path.
 ///
 /// The [festivalId] and [path] must not be empty.