存档重构，游戏内容解锁机制；教程完善（未完成）

Assets/Scripts/UI/SongSelection/PlaySongUI.cs

@@ -19,12 +19,37 @@ namespace Ichni.Menu
             enterGameButton.onClick.AddListener(EnterGame);
         }
 
+        /// <summary>
+        /// 设置标准 Play 按钮是否允许进入游戏。
+        /// 当当前歌曲没有可用难度时由 DifficultySelectionContainer 关闭；歌曲锁定仍沿用原有的独立判断。
+        /// </summary>
+        public void SetEnterGameAvailable(bool isAvailable)
+        {
+            enterGameButton.interactable = isAvailable;
+        }
+
         private void EnterGame()
         {
-            if (MenuManager.instance.songSelectionUIPage.songListController.selectedTab.isLocked)
+            SongSelectionUIPage songSelectionUIPage = MenuManager.instance.songSelectionUIPage;
+            SongSelectionTab selectedTab = songSelectionUIPage.songListController.selectedTab;
+
+            // 即使 Button 的 interactable 状态被错误地恢复，也不能把空难度传给 InformationTransistor。
+            if (songSelectionUIPage.selectedSong == null || songSelectionUIPage.selectedDifficulty == null || selectedTab == null)
             {
                 return;
             }
+
+            // 不能只读取 Tab 的旧显示状态。解锁 Key 可能刚被剧情授予，或 UI 状态被其它逻辑改写；
+            // 标准 Play 与快速点击都会回到 UnlockSaveModule 的同一最终授权判断。
+            UnlockSaveModule unlockSaveModule = GameSaveManager.instance?.UnlockSaveModule;
+            if (unlockSaveModule == null || !unlockSaveModule.CanEnterSong(
+                    ChapterSelectionManager.instance?.currentChapter,
+                    songSelectionUIPage.selectedSong))
+            {
+                return;
+            }
+
+            selectedTab.RefreshUnlockState();
             
             if (MenuManager.instance.isEnteringGame)
             {
@@ -34,9 +59,9 @@ namespace Ichni.Menu
             MenuManager.instance.isEnteringGame = true;
             
             InformationTransistor.instance.SetInformation(
-                ChapterSelectionManager.instance.currentChapter, 
-                MenuManager.instance.songSelectionUIPage.selectedSong, 
-                MenuManager.instance.songSelectionUIPage.selectedDifficulty);
+                ChapterSelectionManager.instance.currentChapter,
+                songSelectionUIPage.selectedSong,
+                songSelectionUIPage.selectedDifficulty);
             AudioManager.Post(AK.EVENTS.ENTERTOGAME);
             SongSelectionManager.instance.StopPreviewSong();
             
@@ -61,4 +86,4 @@ namespace Ichni.Menu
             arrowSeq.Play();
         }
     }
-}
+}