refresh borders of sentences

android/oral-trainer-sdk/src/main/java/cn/learningpad/oraltrainer/sdk/OralTrainerController.kt

@@ -141,6 +141,28 @@ class OralTrainerController internal constructor(
         loadItems(listOf(item))
     }
 
+    /**
+     * Replaces sentences without preparing/reloading media, preserving playback
+     * position and state so a background boundary refresh can apply immediately.
+     */
+    fun updateSentences(mediaId: String, sentences: List<SentenceBoundary>): Boolean {
+        val index = mediaItems.indexOfFirst { it.id == mediaId }
+        if (index < 0) {
+            return false
+        }
+        val updatedItem = mediaItems[index].copy(sentences = sentences)
+        if (mediaItems[index] == updatedItem) {
+            return true
+        }
+        mediaItems[index] = updatedItem
+        if (index == player.currentMediaItemIndex) {
+            listeners.forEach { it.onMediaChanged(updatedItem) }
+            notifySentenceIfChanged(force = true)
+            notifySnapshot()
+        }
+        return true
+    }
+
     fun play() {
         player.play()
     }

android/oral-trainer-sdk/src/main/java/cn/learningpad/oraltrainer/sdk/SentenceBoundaryApi.kt

@@ -111,6 +111,7 @@ class SentenceBoundaryApi internal constructor(
                 connection.requestMethod = "GET"
                 connection.connectTimeout = config.connectTimeoutMs
                 connection.readTimeout = config.readTimeoutMs
+                connection.useCaches = false
                 connection.setRequestProperty("Accept", "application/json")
                 connection.setRequestProperty("User-Agent", config.userAgent)
                 val statusCode = connection.responseCode