feat: TTS audio cache in Room — skip regeneration on replay

- MessageEntity gets ttsUrl + ttsVoice fields (Room version 2→3)
- MessageDao.getTtsUrl() checks cache before API call
- MessageDao.updateTts() saves URL + voice after generation
- readAloud() checks Room first, only calls /api/v1/audio-gen on miss
- Voice change invalidates cache automatically (query includes voice)
- Default voice "Kore" (Gemini-TTS)

app/src/main/java/dev/kaizen/app/chat/ChatScreen.kt

@@ -227,23 +227,7 @@ fun ChatScreen(
         }
     }
 
-    fun readAloud(content: String, messageId: Long) {
-        val cfg = session.config ?: return
-        if (playingTtsForId == messageId) {
-            ttsPlayerRef.value?.release()
-            ttsPlayerRef.value = null
-            playingTtsForId = null
-            return
-        }
-        ttsPlayerRef.value?.release()
-        playingTtsForId = messageId
-        scope.launch {
-            val url = KaizenApi.generateSpeech(cfg.baseUrl, cfg.token, content)
-            if (url == null) {
-                playingTtsForId = null
-                Toast.makeText(context, context.getString(R.string.chat_tts_error), Toast.LENGTH_SHORT).show()
-                return@launch
-            }
+    fun playTtsUrl(url: String, messageId: Long) {
         try {
             val player = MediaPlayer().apply {
                 setDataSource(url)
@@ -266,6 +250,33 @@ fun ChatScreen(
             playingTtsForId = null
         }
     }
+
+    fun readAloud(content: String, messageId: Long, wireId: String) {
+        val cfg = session.config ?: return
+        if (playingTtsForId == messageId) {
+            ttsPlayerRef.value?.release()
+            ttsPlayerRef.value = null
+            playingTtsForId = null
+            return
+        }
+        ttsPlayerRef.value?.release()
+        playingTtsForId = messageId
+        val voice = "Kore"
+        scope.launch {
+            val cached = chat.messageDao.getTtsUrl(wireId, voice)
+            if (cached != null) {
+                playTtsUrl(cached, messageId)
+                return@launch
+            }
+            val url = KaizenApi.generateSpeech(cfg.baseUrl, cfg.token, content, voice)
+            if (url == null) {
+                playingTtsForId = null
+                Toast.makeText(context, context.getString(R.string.chat_tts_error), Toast.LENGTH_SHORT).show()
+                return@launch
+            }
+            chat.messageDao.updateTts(wireId, url, voice)
+            playTtsUrl(url, messageId)
+        }
     }
 
     LaunchedEffect(session.config?.baseUrl, session.config?.token) {
@@ -737,7 +748,7 @@ fun ChatScreen(
                                             }
                                         } else null,
                                         onReadAloud = if (message.role == Role.Assistant && !message.streaming && message.content.isNotBlank()) { content ->
-                                            readAloud(content, message.id)
+                                            readAloud(content, message.id, message.wireId)
                                         } else null,
                                         isPlayingTts = playingTtsForId == message.id,
                                     )

app/src/main/java/dev/kaizen/app/chat/ChatViewModel.kt

@@ -8,5 +8,6 @@ import dev.kaizen.app.db.MessageRepository
 class ChatViewModel(context: Context) {
     private val db = KaizenDatabase.get(context)
     val conversationRepo = ConversationRepository(db.conversationDao())
-    val messageRepo = MessageRepository(db.messageDao())
+    val messageDao = db.messageDao()
+    val messageRepo = MessageRepository(messageDao)
 }

app/src/main/java/dev/kaizen/app/db/Entities.kt

@@ -36,4 +36,6 @@ data class MessageEntity(
     val sortOrder: Int,
     val reasoning: String? = null,
     val sources: List<SearchSource> = emptyList(),
+    val ttsUrl: String? = null,
+    val ttsVoice: String? = null,
 )

app/src/main/java/dev/kaizen/app/db/KaizenDatabase.kt

@@ -8,7 +8,7 @@ import androidx.room.TypeConverters
 
 @Database(
     entities = [ConversationEntity::class, MessageEntity::class],
-    version = 2,
+    version = 3,
     exportSchema = false,
 )
 @TypeConverters(Converters::class)

app/src/main/java/dev/kaizen/app/db/MessageDao.kt

@@ -21,4 +21,10 @@ interface MessageDao {
 
     @Query("SELECT DISTINCT conversationId FROM messages")
     suspend fun cachedConversationIds(): List<String>
+
+    @Query("UPDATE messages SET ttsUrl = :url, ttsVoice = :voice WHERE id = :messageId")
+    suspend fun updateTts(messageId: String, url: String, voice: String)
+
+    @Query("SELECT ttsUrl FROM messages WHERE id = :messageId AND ttsVoice = :voice")
+    suspend fun getTtsUrl(messageId: String, voice: String): String?
 }