fix: 출시 전 검수 이슈 4건 수정

- save_data: JSON 캐스팅 시 null 안전 처리 (손상된 세이브 크래시 방지)
- settings_repository: _prefs! 강제 언래핑 제거, _getPrefs() 패턴 적용
- game_session_controller: IAP 구매 상태를 MonetizationState에 동기화
- iap_service: InAppPurchase.instance를 lazy 초기화로 변경

lib/src/core/engine/iap_service.dart

@@ -68,7 +68,7 @@ class IAPService {
   // 상태
   // ===========================================================================
 
-  final InAppPurchase _iap = InAppPurchase.instance;
+  late final InAppPurchase _iap = InAppPurchase.instance;
 
   bool _isInitialized = false;
   bool _isAvailable = false;

lib/src/core/model/save_data.dart

@@ -148,11 +148,16 @@ class GameSave {
   }
 
   static GameSave fromJson(Map<String, dynamic> json) {
-    final traitsJson = json['traits'] as Map<String, dynamic>;
-    final statsJson = json['stats'] as Map<String, dynamic>;
-    final inventoryJson = json['inventory'] as Map<String, dynamic>;
-    final equipmentJson = json['equipment'] as Map<String, dynamic>;
-    final progressJson = json['progress'] as Map<String, dynamic>;
+    final traitsJson =
+        json['traits'] as Map<String, dynamic>? ?? <String, dynamic>{};
+    final statsJson =
+        json['stats'] as Map<String, dynamic>? ?? <String, dynamic>{};
+    final inventoryJson =
+        json['inventory'] as Map<String, dynamic>? ?? <String, dynamic>{};
+    final equipmentJson =
+        json['equipment'] as Map<String, dynamic>? ?? <String, dynamic>{};
+    final progressJson =
+        json['progress'] as Map<String, dynamic>? ?? <String, dynamic>{};
     final queueJson = (json['queue'] as List<dynamic>? ?? []).cast<dynamic>();
     final skillsJson = (json['skills'] as List<dynamic>? ?? []).cast<dynamic>();
 

lib/src/core/storage/settings_repository.dart

@@ -12,55 +12,56 @@ class SettingsRepository {
   SharedPreferences? _prefs;
 
   /// SharedPreferences 초기화
-  Future<void> init() async {
+  Future<SharedPreferences> _getPrefs() async {
     _prefs ??= await SharedPreferences.getInstance();
+    return _prefs!;
   }
 
   /// 언어 설정 저장
   Future<void> saveLocale(String locale) async {
-    await init();
-    await _prefs!.setString(_keyLocale, locale);
+    final prefs = await _getPrefs();
+    await prefs.setString(_keyLocale, locale);
   }
 
   /// 언어 설정 불러오기
   Future<String?> loadLocale() async {
-    await init();
-    return _prefs!.getString(_keyLocale);
+    final prefs = await _getPrefs();
+    return prefs.getString(_keyLocale);
   }
 
   /// BGM 볼륨 저장 (0.0 ~ 1.0)
   Future<void> saveBgmVolume(double volume) async {
-    await init();
-    await _prefs!.setDouble(_keyBgmVolume, volume.clamp(0.0, 1.0));
+    final prefs = await _getPrefs();
+    await prefs.setDouble(_keyBgmVolume, volume.clamp(0.0, 1.0));
   }
 
   /// BGM 볼륨 불러오기 (기본값: 0.7)
   Future<double> loadBgmVolume() async {
-    await init();
-    return _prefs!.getDouble(_keyBgmVolume) ?? 0.7;
+    final prefs = await _getPrefs();
+    return prefs.getDouble(_keyBgmVolume) ?? 0.7;
   }
 
   /// SFX 볼륨 저장 (0.0 ~ 1.0)
   Future<void> saveSfxVolume(double volume) async {
-    await init();
-    await _prefs!.setDouble(_keySfxVolume, volume.clamp(0.0, 1.0));
+    final prefs = await _getPrefs();
+    await prefs.setDouble(_keySfxVolume, volume.clamp(0.0, 1.0));
   }
 
   /// SFX 볼륨 불러오기 (기본값: 0.8)
   Future<double> loadSfxVolume() async {
-    await init();
-    return _prefs!.getDouble(_keySfxVolume) ?? 0.8;
+    final prefs = await _getPrefs();
+    return prefs.getDouble(_keySfxVolume) ?? 0.8;
   }
 
   /// 애니메이션 속도 저장 (0.5 ~ 2.0, 1.0이 기본)
   Future<void> saveAnimationSpeed(double speed) async {
-    await init();
-    await _prefs!.setDouble(_keyAnimationSpeed, speed.clamp(0.5, 2.0));
+    final prefs = await _getPrefs();
+    await prefs.setDouble(_keyAnimationSpeed, speed.clamp(0.5, 2.0));
   }
 
   /// 애니메이션 속도 불러오기 (기본값: 1.0)
   Future<double> loadAnimationSpeed() async {
-    await init();
-    return _prefs!.getDouble(_keyAnimationSpeed) ?? 1.0;
+    final prefs = await _getPrefs();
+    return prefs.getDouble(_keyAnimationSpeed) ?? 1.0;
   }
 }

lib/src/features/game/game_session_controller.dart

@@ -1,5 +1,6 @@
 import 'dart:async';
 
+import 'package:asciineverdie/src/core/engine/iap_service.dart';
 import 'package:asciineverdie/src/core/engine/progress_loop.dart';
 import 'package:asciineverdie/src/core/engine/progress_service.dart';
 import 'package:asciineverdie/src/core/model/game_state.dart';
@@ -173,6 +174,17 @@ class GameSessionController extends ChangeNotifier {
     _status = GameSessionStatus.running;
     _cheatsEnabled = cheatsEnabled;
 
+    // IAP 구매 상태를 MonetizationState에 동기화
+    // (테스트 환경에서는 InAppPurchase 플랫폼 채널 미등록으로 예외 발생 가능)
+    try {
+      final isPaid = IAPService.instance.isAdRemovalPurchased;
+      if (_monetization.adRemovalPurchased != isPaid) {
+        _monetization = _monetization.copyWith(adRemovalPurchased: isPaid);
+      }
+    } catch (_) {
+      // 비모바일 플랫폼 또는 테스트 환경에서는 무시
+    }
+
     // 통계 초기화
     if (isNewGame) {
       await _statisticsManager.initializeForNewGame();
@@ -273,8 +285,16 @@ class GameSessionController extends ChangeNotifier {
       return;
     }
 
-    // 저장된 수익화 상태 복원
+    // 저장된 수익화(monetization) 상태 복원, IAP 구매 상태 동기화
     _monetization = savedMonetization ?? MonetizationState.initial();
+    try {
+      final isPaid = IAPService.instance.isAdRemovalPurchased;
+      if (_monetization.adRemovalPurchased != isPaid) {
+        _monetization = _monetization.copyWith(adRemovalPurchased: isPaid);
+      }
+    } catch (_) {
+      // 비모바일 플랫폼 또는 테스트 환경에서는 무시
+    }
 
     // 복귀 보상 체크 (Phase 7)
     _returnRewardsManager.checkReturnRewards(