feat: harden geofence and distance diagnostics

lib/features/homes/services/geofence_runtime_store.dart

@@ -0,0 +1,53 @@
+import 'dart:convert';
+
+import 'package:shared_preferences/shared_preferences.dart';
+
+import '../models/geofence_runtime_state.dart';
+
+class GeofenceRuntimeStore {
+  static const String _runtimeKey = 'ignis_geofence_runtime';
+
+  Future<GeofenceRuntimeState> load() async {
+    final prefs = await SharedPreferences.getInstance();
+    final raw = prefs.getString(_runtimeKey);
+    if (raw == null || raw.isEmpty) {
+      return const GeofenceRuntimeState();
+    }
+
+    final decoded = jsonDecode(raw);
+    if (decoded is! Map<String, dynamic>) {
+      return const GeofenceRuntimeState();
+    }
+
+    return GeofenceRuntimeState.fromJson(decoded);
+  }
+
+  Future<void> save(GeofenceRuntimeState state) async {
+    final prefs = await SharedPreferences.getInstance();
+    final data = state.toJson();
+    if (data.isEmpty) {
+      await prefs.remove(_runtimeKey);
+      return;
+    }
+
+    await prefs.setString(_runtimeKey, jsonEncode(data));
+  }
+
+  Future<GeofenceRuntimeState> armForHome(String homeId) async {
+    final next = (await load()).armForHome(homeId);
+    await save(next);
+    return next;
+  }
+
+  Future<GeofenceRuntimeState> disarm() async {
+    final next = (await load()).disarm();
+    await save(next);
+    return next;
+  }
+
+  Future<GeofenceRuntimeState> removeHome(String homeId) async {
+    final next = (await load()).removeHome(homeId);
+    await save(next);
+    return next;
+  }
+}