diff --git a/app/src/main/java/com/example/login_v3/data/api/api_class/DM_Basic.kt b/app/src/main/java/com/example/login_v3/data/api/api_class/DM_Basic.kt
index 1c5aa38..6824864 100644
--- a/app/src/main/java/com/example/login_v3/data/api/api_class/DM_Basic.kt
+++ b/app/src/main/java/com/example/login_v3/data/api/api_class/DM_Basic.kt
@@ -124,7 +124,13 @@ data class Message(
     var aspectRatio: Float? = null,
 
     @kotlin.jvm.Transient
-    var callLogInfo: CallLogInfo? = null
+    var callLogInfo: CallLogInfo? = null,
+
+    @kotlin.jvm.Transient
+    var isDownloaded: Boolean = false,
+
+    @kotlin.jvm.Transient
+    var localPath: String? = null
 ) {
     init {
         if (type == "system" || type.startsWith("call")) {
diff --git a/app/src/main/java/com/example/login_v3/data/di/AppDatabase.kt b/app/src/main/java/com/example/login_v3/data/di/AppDatabase.kt
index 22c6b9e..bf2adcb 100644
--- a/app/src/main/java/com/example/login_v3/data/di/AppDatabase.kt
+++ b/app/src/main/java/com/example/login_v3/data/di/AppDatabase.kt
@@ -19,7 +19,7 @@ import com.example.login_v3.data.local.entities.RoomLocalEntity
         RoomLocalEntity::class,
         BlockedUserLocalEntity::class
     ],
-    version = 2,
+    version = 3,
     exportSchema = false
 )
 @TypeConverters(RoomConverters::class)
diff --git a/app/src/main/java/com/example/login_v3/data/local/dao/MessageDao.kt b/app/src/main/java/com/example/login_v3/data/local/dao/MessageDao.kt
index 382a8dc..ebaef09 100644
--- a/app/src/main/java/com/example/login_v3/data/local/dao/MessageDao.kt
+++ b/app/src/main/java/com/example/login_v3/data/local/dao/MessageDao.kt
@@ -25,9 +25,32 @@ interface MessageDao {
     @Query("DELETE FROM messages WHERE id = :id")
     suspend fun deleteById(id: String)
 
+    @Query("SELECT id FROM messages WHERE chatRoomId = :roomId ORDER BY createdAt DESC LIMIT 1")
+    suspend fun getLatestMessageId(roomId: String): String?
+
     @Transaction
     suspend fun replaceTempMessageWithSuccess(tempId: String, successEntity: MessageEntity) {
         deleteById(tempId)
         insertOrUpdate(successEntity)
     }
+
+    @Transaction
+    suspend fun insertOrUpdateListPreservingLocalData(messages: List<MessageEntity>) {
+        messages.forEach { msg ->
+            val existing = getMessageById(msg.id)
+            if (existing != null) {
+                // 🎯 核心：保留本地已下載的標記與路徑，其餘由網路資料覆蓋
+                val updated = msg.copy(
+                    isDownloaded = existing.isDownloaded,
+                    localPath = existing.localPath
+                )
+                insertOrUpdate(updated)
+            } else {
+                insertOrUpdate(msg)
+            }
+        }
+    }
+
+    @Query("UPDATE messages SET isDownloaded = :isDownloaded, localPath = :localPath WHERE id = :messageId")
+    suspend fun updateDownloadStatus(messageId: String, isDownloaded: Boolean, localPath: String?)
 }
diff --git a/app/src/main/java/com/example/login_v3/data/local/entities/MessageEntity.kt b/app/src/main/java/com/example/login_v3/data/local/entities/MessageEntity.kt
index a776225..247ba47 100644
--- a/app/src/main/java/com/example/login_v3/data/local/entities/MessageEntity.kt
+++ b/app/src/main/java/com/example/login_v3/data/local/entities/MessageEntity.kt
@@ -21,5 +21,7 @@ data class MessageEntity(
     val status: MessageStatus,
     val reactions: List<Reaction>?,
     val attachment: Attachment? = null,
-    val aspectRatio: Float? = null
+    val aspectRatio: Float? = null,
+    val isDownloaded: Boolean = false, // 👈 新增：標記媒體/訊息是否已下載到本地
+    val localPath: String? = null      // 👈 新增：儲存本地檔案路徑
 )
diff --git a/app/src/main/java/com/example/login_v3/data/repository/dm/DM_Basic_Repository.kt b/app/src/main/java/com/example/login_v3/data/repository/dm/DM_Basic_Repository.kt
index a9937af..f1ea9d3 100644
--- a/app/src/main/java/com/example/login_v3/data/repository/dm/DM_Basic_Repository.kt
+++ b/app/src/main/java/com/example/login_v3/data/repository/dm/DM_Basic_Repository.kt
@@ -121,8 +121,8 @@ class ChatRoomsRepository @Inject constructor(
                             aspectRatio = payload.attachment?.let { if (it.width > 0 && it.height > 0) it.width.toFloat() / it.height.toFloat() else null }
                         )
 
-                        // 3. 寫入本地資料庫
-                        messageDao.insertOrUpdate(entity)
+                        // 3. 寫入本地資料庫 (同樣使用保留本地標記的版本)
+                        messageDao.insertOrUpdateListPreservingLocalData(listOf(entity))
                         Log.d("ChatRoomsRepository", "WebSocket 訊息成功寫入資料庫: ${entity.content}")
 
                     } else if (event?.type == "dm:typing") {
@@ -192,6 +192,8 @@ class ChatRoomsRepository @Inject constructor(
                     attachment = entity.attachment
                 ).apply {
                     aspectRatio = entity.aspectRatio
+                    isDownloaded = entity.isDownloaded // 👈 新增
+                    localPath = entity.localPath       // 👈 新增
                 }
             }
 
@@ -244,9 +246,8 @@ class ChatRoomsRepository @Inject constructor(
                         )
                     }
 
-                    // 3. 寫入資料庫
-                    // 因為你寫了 OnConflictStrategy.REPLACE，歷史訊息會被乖乖追加進去，不會影響現有訊息！
-                    messageDao.insertOrUpdateList(entities)
+                    // 3. 寫入資料庫 (使用優化過的版本，保留本地下載狀態)
+                    messageDao.insertOrUpdateListPreservingLocalData(entities)
 
                     // 🎯 4. 關鍵：把整個 body 回傳回去（包含 nextCursor 和 hasMore）
                     // 這樣 ViewModel 才能知道下一次往上滑時，要帶哪一個 cursor！
@@ -366,6 +367,18 @@ class ChatRoomsRepository @Inject constructor(
         }
     }
 
+    suspend fun getLatestMessageId(roomId: String): String? {
+        Log.d("ChatDebug", "💾 [Repository] 正在查詢本地最新訊息 ID... roomId: $roomId")
+        return try {
+            val id = messageDao.getLatestMessageId(roomId)
+            Log.d("ChatDebug", "💾 [Repository] 本地最新 ID: $id")
+            id
+        } catch (e: Exception) {
+            Log.e("ChatDebug", "❌ [Repository] 查詢最新 ID 失敗", e)
+            null
+        }
+    }
+
 
     //upload file
     suspend fun uploadAttachment(roomId: String, fileUri: Uri): Result<Message> {
@@ -613,7 +626,7 @@ class ChatRoomsRepository @Inject constructor(
 
     //download file
     private val httpClient = OkHttpClient()
-    fun downloadFileFromUrlFlow(fileUrl: String, fileName: String): Flow<Result<Float>> = flow {
+    fun downloadFileFromUrlFlow(messageId: String, fileUrl: String, fileName: String): Flow<Result<Float>> = flow {
         // 🎯 1. 檢查並自動拼接完整的 Base URL
         val finalUrl = if (fileUrl.startsWith("http://") || fileUrl.startsWith("https://")) {
             fileUrl
@@ -651,8 +664,9 @@ class ChatRoomsRepository @Inject constructor(
             }
 
             val totalBytes = body.contentLength()
-            // 🎯 修正後的寫法：直接存入手機系統的公共 Download 資料夾
-            val targetDirectory = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS)
+            // 🎯 修正後的寫法：存入 app 專屬資料夾，避免被使用者手動刪除或污染 Download 資料夾
+            // 如果希望使用者也能看到，可以維持 Environment.DIRECTORY_DOWNLOADS
+            val targetDirectory = context.getExternalFilesDir(Environment.DIRECTORY_PICTURES) ?: context.filesDir
             val targetFile = File(targetDirectory, fileName)
 
             var bytesCopied = 0L
@@ -675,6 +689,10 @@ class ChatRoomsRepository @Inject constructor(
                 }
             }
 
+            // 🎯 關鍵：下載成功後更新資料庫狀態
+            messageDao.updateDownloadStatus(messageId, true, targetFile.absolutePath)
+            Log.d("ChatDebug", "✅ 檔案下載完成且已更新資料庫: ${targetFile.absolutePath}")
+
             emit(Result.success(1.0f))
 
         } catch (e: Exception) {
diff --git a/app/src/main/java/com/example/login_v3/home/Message/UI/Detail/MessageUiModel.kt b/app/src/main/java/com/example/login_v3/home/Message/UI/Detail/MessageUiModel.kt
index fd31303..e5489c1 100644
--- a/app/src/main/java/com/example/login_v3/home/Message/UI/Detail/MessageUiModel.kt
+++ b/app/src/main/java/com/example/login_v3/home/Message/UI/Detail/MessageUiModel.kt
@@ -29,7 +29,9 @@ data class MessageUiModel(
     val isFile: Boolean,
     val mediaUrl: String,
     val thumbnailUrl: String? = null,
-    val aspectRatio: Float? = null
+    val aspectRatio: Float? = null,
+    val isDownloaded: Boolean = false, // 👈 新增
+    val localPath: String? = null      // 👈 新增
 )
 
 fun Message.toUiModel(): MessageUiModel {
@@ -43,6 +45,13 @@ fun Message.toUiModel(): MessageUiModel {
         else "$baseUrl${if (raw.startsWith("/")) "" else "/"}$raw"
     }
 
+    // 🎯 核心邏輯：如果已經下載完成，且本地路徑存在，則 mediaUrl 優先指向本地檔案
+    val finalMediaUrl = if (isDownloaded && !localPath.isNullOrBlank()) {
+        "file://$localPath"
+    } else {
+        mediaUrl
+    }
+
     return MessageUiModel(
         id = id,
         senderId = senderId,
@@ -62,8 +71,10 @@ fun Message.toUiModel(): MessageUiModel {
         isVideo = isVideo,
         isAudio = isAudio,
         isFile = isFile,
-        mediaUrl = mediaUrl,
+        mediaUrl = finalMediaUrl, // 👈 使用判斷後的 URL
         thumbnailUrl = finalThumbnailUrl,
-        aspectRatio = finalAspectRatio
+        aspectRatio = finalAspectRatio,
+        isDownloaded = isDownloaded,
+        localPath = localPath
     )
 }
diff --git a/app/src/main/java/com/example/login_v3/home/Message/ViewModel/Detail/Message_Messaging_ViewModel.kt b/app/src/main/java/com/example/login_v3/home/Message/ViewModel/Detail/Message_Messaging_ViewModel.kt
index 7cc6ac4..0f30836 100644
--- a/app/src/main/java/com/example/login_v3/home/Message/ViewModel/Detail/Message_Messaging_ViewModel.kt
+++ b/app/src/main/java/com/example/login_v3/home/Message/ViewModel/Detail/Message_Messaging_ViewModel.kt
@@ -202,17 +202,45 @@ class ChatViewModel @Inject constructor(
     }
 
     private fun initChat(roomId: String) {
+        Log.d("ChatDebug", "🛠️ [ViewModel] initChat 開始 | roomId: $roomId")
         viewModelScope.launch {
             // 啟動 Session
-            try { repository.startChatSession(roomId) } catch (e: Exception) { Log.e("ChatViewModel", "WS Error", e) }
+            try { 
+                Log.d("ChatDebug", "🌐 [ViewModel] 嘗試啟動 WebSocket Session...")
+                repository.startChatSession(roomId) 
+            } catch (e: Exception) { 
+                Log.e("ChatDebug", "❌ [ViewModel] WS Error", e) 
+            }
 
-            // 背景同步
-            repository.refreshChatMessages(roomId, cursor = null, limit = 20)
-                .onSuccess { response ->
-                    nextCursor = response.nextCursor
-                    hasMore = response.hasMore
+            // 🎯 核心優化：Delta-Sync 邏輯
+            try {
+                Log.d("ChatDebug", "🔍 [ViewModel] 正在檢查本地資料一致性...")
+                val currentRoom = repository.getChatRoomFlow(roomId).first()
+                val localLatestId = repository.getLatestMessageId(roomId)
+                val serverLatestId = currentRoom?.lastMessage?.id
+
+                Log.d("ChatDebug", "📊 [ViewModel] 比較結果 - LocalLatest: $localLatestId | ServerLatest: $serverLatestId")
+
+                if (localLatestId == null || localLatestId != serverLatestId) {
+                    Log.d("ChatDebug", "🔄 [ViewModel] 資料不一致，發起增量同步...")
+                    // 背景同步
+                    repository.refreshChatMessages(roomId, cursor = null, limit = 20)
+                        .onSuccess { response ->
+                            nextCursor = response.nextCursor
+                            hasMore = response.hasMore
+                            Log.d("ChatDebug", "✅ [ViewModel] 同步成功 | nextCursor: $nextCursor")
+                            repository.markAsRead(roomId)
+                        }
+                        .onFailure { e ->
+                            Log.e("ChatDebug", "❌ [ViewModel] 同步失敗: ${e.message}")
+                        }
+                } else {
+                    Log.d("ChatDebug", "✅ [ViewModel] 資料已是最新，跳過 refresh")
                     repository.markAsRead(roomId)
                 }
+            } catch (e: Exception) {
+                Log.e("ChatDebug", "❌ [ViewModel] initChat 執行過程發生異常", e)
+            }
         }
     }
 
@@ -536,8 +564,8 @@ class ChatViewModel @Inject constructor(
         viewModelScope.launch {
             fileDownloadStates[messageId] = DownloadStatus.Downloading(0f)
 
-            // 呼叫剛剛改好的 URL 版 Flow
-            repository.downloadFileFromUrlFlow(fileUrl, displayFileName)
+            // 呼叫剛剛改好的 URL 版 Flow，傳入 messageId
+            repository.downloadFileFromUrlFlow(messageId, fileUrl, displayFileName)
                 .collect { progressResult ->
                     progressResult.onSuccess { progress ->
                         if (progress >= 1.0f) {
diff --git a/app/src/main/java/com/example/login_v3/home/setting/Setting_list_Screen.kt b/app/src/main/java/com/example/login_v3/home/setting/Setting_list_Screen.kt
index 9b6da2f..7e27e53 100644
--- a/app/src/main/java/com/example/login_v3/home/setting/Setting_list_Screen.kt
+++ b/app/src/main/java/com/example/login_v3/home/setting/Setting_list_Screen.kt
@@ -159,6 +159,7 @@ fun SharedTransitionScope.setting_list_Screen(
                                 style = MaterialTheme.typography.titleMedium,
                                 fontSize = 24.sp,
                                 fontWeight = FontWeight.Bold,
+                                color = MaterialTheme.colorScheme.onBackground,
                                 modifier = Modifier
                                     .sharedElement(
                                         sharedContentState = titleState,
@@ -173,7 +174,7 @@ fun SharedTransitionScope.setting_list_Screen(
                             item.description?.let {
                                 Text(text = it,
                                     style = MaterialTheme.typography.bodySmall,
-                                    color = Color.White
+                                    color = MaterialTheme.colorScheme.onSecondary
                                 )
                             }
                         }
diff --git a/app/src/main/java/com/example/login_v3/ui/theme/Color.kt b/app/src/main/java/com/example/login_v3/ui/theme/Color.kt
index f509916..47a484b 100644
--- a/app/src/main/java/com/example/login_v3/ui/theme/Color.kt
+++ b/app/src/main/java/com/example/login_v3/ui/theme/Color.kt
@@ -19,6 +19,9 @@ val DarkGlass = Color(0x14000000)
 val WhiteText = Color(0xFFFFFFFF)
 val DarkText = Color(0xFF000000)
 
+val sub_WhiteText = Color(0xFFD0D0D0)
+val sub_DarkText = Color(0xFFD0D0D0)
+
 //default background
 
 val White_default = Color(0xFF2C2C2C)
diff --git a/app/src/main/java/com/example/login_v3/ui/theme/Theme.kt b/app/src/main/java/com/example/login_v3/ui/theme/Theme.kt
index 949fe13..7e0fae7 100644
--- a/app/src/main/java/com/example/login_v3/ui/theme/Theme.kt
+++ b/app/src/main/java/com/example/login_v3/ui/theme/Theme.kt
@@ -17,7 +17,8 @@ private val DarkColorScheme = darkColorScheme(
     secondary = light_orange,
     tertiary = Pink80,
     background = Color(0xFF121212),
-    onBackground = DarkText
+    onBackground = WhiteText,
+    onSecondary = sub_DarkText,
 )
 
 private val LightColorScheme = lightColorScheme(
@@ -25,7 +26,8 @@ private val LightColorScheme = lightColorScheme(
     secondary = light_orange,
     tertiary = Pink40,
     background = Color(0xFF121212),
-    onBackground = WhiteText
+    onBackground = DarkText,
+    onSecondary = sub_WhiteText,
 
     /* Other default colors to override