fix a bug

ios/OralTrainer/Views/TestView.swift

@@ -58,13 +58,16 @@ struct TestView: View {
                 }
                 HStack(spacing: 8) {
                     sentenceButton("上一句") {
+                        stopDubPlayback(message: nil)
                         controller.seekToPreviousSentence()
                     }
                     sentenceButton("播放原句") {
+                        stopDubPlayback(message: nil)
                         controller.playCurrentSentenceAndStop()
                         controller.showTransientMessage("正在播放当前句子，播放完自动停止")
                     }
                     sentenceButton("下一句") {
+                        stopDubPlayback(message: nil)
                         controller.seekToNextSentence()
                     }
                 }
@@ -80,19 +83,24 @@ struct TestView: View {
                 .buttonStyle(.plain)
                 .disabled(isAssessing)
                 HStack(spacing: 8) {
-                    dubButton("播放配音", enabled: !dubSegments.isEmpty && !dubbingPlayback && !isGeneratingDub) {
+                    dubButton(
+                        dubbingPlayback ? "停止播放" : "播放本句录音",
+                        enabled: dubbingPlayback || (controller.currentSentence.flatMap { dubSegments[$0.index] } != nil)
+                    ) {
                         toggleDubPlayback()
                     }
                     dubButton("生成配音", enabled: !dubRawSegments.isEmpty && !dubbingPlayback && !isGeneratingDub) {
+                        stopDubPlayback(message: nil)
                         generateDubShareAudio()
                     }
                     dubButton("分享配音", enabled: mergedDubURL != nil && !dubbingPlayback && !isSharingDub) {
+                        stopDubPlayback(message: nil)
                         shareMergedDub()
                     }
                 }
                 Text(dubbingStatus)
                     .font(.system(size: 13))
-                    .foregroundColor(Theme.accentDeep)
+                    .foregroundColor(isSharingDub ? Theme.danger : Theme.accentDeep)
                     .frame(maxWidth: .infinity, alignment: .leading)
                 Text(scoreSummary)
                     .font(.system(size: 22, weight: .bold))
@@ -159,6 +167,7 @@ struct TestView: View {
     // MARK: - 录音
 
     private func toggleRecording() {
+        stopDubPlayback(message: nil)
         if isRecording {
             stopRecordingAndAssess()
         } else {
@@ -394,32 +403,40 @@ struct TestView: View {
 
     private func toggleDubPlayback() {
         if dubbingPlayback {
-            stopDubPlayback(message: "已停止配音播放")
+            stopDubPlayback(message: "已停止录音播放")
             return
         }
-        let sentence = controller.currentSentence
-        let audioURL = mergedDubURL ?? sentence.flatMap { dubSegments[$0.index] }
-        guard let audioURL else { return }
-        if mergedDubURL == nil, let sentence = sentence {
-            controller.seek(to: sentence.startMs)
+        guard let sentence = controller.currentSentence else {
+            dubbingStatus = "请先选择要播放的句子"
+            return
         }
+        guard let audioURL = dubSegments[sentence.index] else {
+            dubbingStatus = "当前句还没有录音，请先录音后再播放"
+            return
+        }
+        // Always play the current sentence recording only (never the merged full track).
+        stopDubPlayback(message: nil)
+        controller.seek(to: sentence.startMs)
         controller.pause()
         controller.setVolume(0)
         let player = dubPlayer ?? AVPlayer()
         dubPlayer = player
-        player.replaceCurrentItem(with: AVPlayerItem(url: audioURL))
+        let item = AVPlayerItem(url: audioURL)
+        player.replaceCurrentItem(with: item)
         dubbingPlayback = true
-        dubbingStatus = mergedDubURL == nil ? "正在播放当前句配音，视频原声静音" : "正在播放整段配音，视频原声静音"
+        dubbingStatus = "正在播放当前句录音"
         player.play()
-        if dubPlaybackObserver == nil {
-            dubPlaybackObserver = NotificationCenter.default.addObserver(
-                forName: AVPlayerItem.didPlayToEndTimeNotification,
-                object: player.currentItem,
-                queue: .main
-            ) { _ in
-                DispatchQueue.main.asyncAfter(deadline: .now() + 0.25) {
-                    stopDubPlayback(message: "配音播放完成")
-                }
+        if let dubPlaybackObserver {
+            NotificationCenter.default.removeObserver(dubPlaybackObserver)
+            self.dubPlaybackObserver = nil
+        }
+        dubPlaybackObserver = NotificationCenter.default.addObserver(
+            forName: AVPlayerItem.didPlayToEndTimeNotification,
+            object: item,
+            queue: .main
+        ) { _ in
+            DispatchQueue.main.asyncAfter(deadline: .now() + 0.25) {
+                stopDubPlayback(message: "本句录音播放完成")
             }
         }
     }
@@ -468,7 +485,7 @@ struct TestView: View {
             return
         }
         isSharingDub = true
-        dubbingStatus = "正在生成分享链接…"
+        dubbingStatus = "正在生成分享链接，请稍候..."
         let request = DubShareUploadRequest(
             videoHash: item.id,
             title: item.title,