Gate auto sync with network reachability checks

lib/core/network/reachability/network_reachability.dart

@@ -0,0 +1,13 @@
+import 'package:relationship_saver/core/network/reachability/network_reachability_stub.dart'
+    if (dart.library.html) 'package:relationship_saver/core/network/reachability/network_reachability_web.dart'
+    if (dart.library.io) 'package:relationship_saver/core/network/reachability/network_reachability_io.dart';
+
+/// Runtime network reachability probe.
+abstract class NetworkReachability {
+  /// Returns `true` when network looks reachable.
+  Future<bool> isReachable({Duration timeout = const Duration(seconds: 2)});
+}
+
+/// Returns platform implementation for network reachability probing.
+NetworkReachability createNetworkReachability() =>
+    createPlatformNetworkReachability();

lib/core/network/reachability/network_reachability_io.dart

@@ -0,0 +1,25 @@
+import 'dart:async';
+import 'dart:io';
+
+import 'package:relationship_saver/core/network/reachability/network_reachability.dart';
+
+class IoNetworkReachability implements NetworkReachability {
+  @override
+  Future<bool> isReachable({
+    Duration timeout = const Duration(seconds: 2),
+  }) async {
+    try {
+      final List<InternetAddress> result = await InternetAddress.lookup(
+        'example.com',
+      ).timeout(timeout);
+      return result.isNotEmpty && result.first.rawAddress.isNotEmpty;
+    } on SocketException {
+      return false;
+    } on TimeoutException {
+      return false;
+    }
+  }
+}
+
+NetworkReachability createPlatformNetworkReachability() =>
+    IoNetworkReachability();

lib/core/network/reachability/network_reachability_provider.dart

@@ -0,0 +1,8 @@
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:relationship_saver/core/network/reachability/network_reachability.dart';
+
+/// Provides runtime reachability implementation used for sync triggers.
+final Provider<NetworkReachability> networkReachabilityProvider =
+    Provider<NetworkReachability>((Ref ref) {
+      return createNetworkReachability();
+    });

lib/core/network/reachability/network_reachability_stub.dart

@@ -0,0 +1,13 @@
+import 'package:relationship_saver/core/network/reachability/network_reachability.dart';
+
+class StubNetworkReachability implements NetworkReachability {
+  @override
+  Future<bool> isReachable({
+    Duration timeout = const Duration(seconds: 2),
+  }) async {
+    return true;
+  }
+}
+
+NetworkReachability createPlatformNetworkReachability() =>
+    StubNetworkReachability();

lib/core/network/reachability/network_reachability_web.dart

@@ -0,0 +1,14 @@
+import 'package:relationship_saver/core/network/reachability/network_reachability.dart';
+
+class WebNetworkReachability implements NetworkReachability {
+  @override
+  Future<bool> isReachable({
+    Duration timeout = const Duration(seconds: 2),
+  }) async {
+    // Web environments vary in available probes; keep optimistic fallback.
+    return true;
+  }
+}
+
+NetworkReachability createPlatformNetworkReachability() =>
+    WebNetworkReachability();

lib/features/sync/sync_auto_trigger_controller.dart

@@ -4,18 +4,22 @@ import 'package:flutter/foundation.dart';
 import 'package:relationship_saver/features/sync/sync_coordinator.dart';
 
 typedef SyncNowRunner = Future<SyncRunResult> Function();
+typedef TriggerGate = Future<bool> Function();
 
 /// Coordinates auto-triggered sync calls with cooldown and concurrency guards.
 class SyncAutoTriggerController {
   SyncAutoTriggerController({
     required SyncNowRunner syncNow,
     required DateTime Function() now,
+    TriggerGate? canTrigger,
     this.minimumInterval = const Duration(minutes: 3),
   }) : _syncNow = syncNow,
-       _now = now;
+       _now = now,
+       _canTrigger = canTrigger ?? _alwaysAllowed;
 
   final SyncNowRunner _syncNow;
   final DateTime Function() _now;
+  final TriggerGate _canTrigger;
   final Duration minimumInterval;
 
   bool _running = false;
@@ -45,6 +49,10 @@ class SyncAutoTriggerController {
       return false;
     }
 
+    if (!await _canTrigger()) {
+      return false;
+    }
+
     _running = true;
     _lastTriggeredAt = now;
     try {
@@ -71,4 +79,6 @@ class SyncAutoTriggerController {
     final int multiplier = 1 << cappedFailures;
     return minimumInterval * multiplier;
   }
+
+  static Future<bool> _alwaysAllowed() async => true;
 }

lib/features/sync/sync_background_runner.dart

@@ -3,6 +3,7 @@ import 'dart:async';
 import 'package:flutter/widgets.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:relationship_saver/core/config/app_config.dart';
+import 'package:relationship_saver/core/network/reachability/network_reachability_provider.dart';
 import 'package:relationship_saver/features/sync/sync_auto_trigger_controller.dart';
 import 'package:relationship_saver/features/sync/sync_coordinator.dart';
 
@@ -31,6 +32,12 @@ class _SyncBackgroundRunnerState extends ConsumerState<SyncBackgroundRunner>
       minimumInterval: Duration(
         seconds: AppConfig.backgroundSyncIntervalSeconds,
       ),
+      canTrigger: () async {
+        if (AppConfig.useFakeBackend) {
+          return true;
+        }
+        return ref.read(networkReachabilityProvider).isReachable();
+      },
     );
     WidgetsBinding.instance.addObserver(this);
     _configurePeriodicRunner();