FIX: 跟读录音参考时长与最大时长按播放倍速换算

- RepeatFlowConfig 新增 playbackSpeed，单句跟读与难句跟读接入
- 参考时长/最大时长按「原句时长 ÷ 倍速」计算，0.8x 时不再因有声时长超过原句时长把动态静音兜底压到 1s 而截断录音
- 新增引擎倍速回归测试

Author: echo-loop

lib/providers/learning_session/review_difficult_practice_provider.dart

@@ -954,6 +954,7 @@ class ReviewDifficultPractice extends _$ReviewDifficultPractice {
       config: RepeatFlowConfig(
         audioItemId: session.audioItemId ?? '',
         promptIdPrefix: 'rdp',
+        playbackSpeed: () => state.settings.playbackSpeed,
         getRepeatCount: (_) => state.targetRepeatCount,
         getIntervalDuration: (s) => listenAndRepeatPauseCalculator(s.duration),
         isManualMode: () => state.isManualMode,

lib/providers/listen_and_repeat/listen_and_repeat_controller.dart

@@ -336,6 +336,8 @@ class ListenAndRepeatController extends _$ListenAndRepeatController {
     final config = RepeatFlowConfig(
       audioItemId: audioItemId,
       promptIdPrefix: 'lar',
+      playbackSpeed: () =>
+          ref.read(listenAndRepeatSettingsProvider).playbackSpeed,
       getRepeatCount: (_) =>
           ref.read(listenAndRepeatSettingsProvider).repeatCount,
       getIntervalDuration: (s) {

lib/providers/repeat_flow/repeat_flow_engine.dart

@@ -63,6 +63,12 @@ class RepeatFlowConfig {
   /// promptId 前缀（默认 'lar'，各页面可自定义）
   final String promptIdPrefix;
 
+  /// 当前播放倍速（默认 1.0）。
+  ///
+  /// 用户跟读的是按此倍速播放后的音频，录音的参考时长与最大时长都按
+  /// 「实际听到的时长」= 原句时长 ÷ 倍速 计算，避免慢速播放时提前截断录音。
+  final double Function()? playbackSpeed;
+
   const RepeatFlowConfig({
     required this.audioItemId,
     required this.getRepeatCount,
@@ -71,6 +77,7 @@ class RepeatFlowConfig {
     this.onBeforeSentenceStart,
     this.onSentencePlayed,
     this.promptIdPrefix = 'lar',
+    this.playbackSpeed,
   });
 }
 
@@ -820,21 +827,37 @@ class RepeatFlowEngine {
       'promptId=$promptId',
     );
 
+    final heardDuration = _heardDuration(sentence);
     final computed =
-        sentence.duration * kRecordingDurationMultiplier +
-        kRecordingTimeoutBase;
+        heardDuration * kRecordingDurationMultiplier + kRecordingTimeoutBase;
     final maxDuration = computed < kRecordingMinTimeout
         ? kRecordingMinTimeout
         : computed;
 
     callbacks.setMaxRecordingDuration(maxDuration);
 
-    AppLogger.log(logTag, '开始录音: $promptId');
+    AppLogger.log(
+      logTag,
+      '开始录音: $promptId referenceDuration=${heardDuration.inMilliseconds}ms '
+      '(原句${sentence.duration.inMilliseconds}ms) '
+      'maxDuration=${maxDuration.inMilliseconds}ms',
+    );
     callbacks.startRecording(
       promptId: promptId,
       referenceText: sentence.text,
       maxDuration: maxDuration,
-      referenceDuration: sentence.duration,
+      referenceDuration: heardDuration,
+    );
+  }
+
+  /// 用户实际听到的句子时长：原句时长 ÷ 播放倍速。
+  ///
+  /// 倍速未配置或非法（≤0、非有限值）时按 1.0x 处理。
+  Duration _heardDuration(Sentence sentence) {
+    final speed = _config.playbackSpeed?.call() ?? 1.0;
+    if (!speed.isFinite || speed <= 0) return sentence.duration;
+    return Duration(
+      microseconds: (sentence.duration.inMicroseconds / speed).round(),
     );
   }
 

test/providers/repeat_flow/repeat_flow_engine_test.dart

@@ -496,4 +496,56 @@ void main() {
     await replay;
     expect(playCalls, 2);
   });
+
+  // 回归：0.8x 播放时用户跟读的是放慢后的音频，参考时长若仍按 1.0x 原句时长，
+  // 有声时长很快超过「原句时长」，动态静音兜底被压到 1s，把仍在说话的用户截断。
+  test('录音参考时长与最大时长按播放倍速换算为实际听到的时长', () async {
+    final recordings = <({Duration max, Duration? reference})>[];
+    final engine = RepeatFlowEngine(
+      onStateChanged: (_) {},
+      callbacks: RepeatFlowCallbacks(
+        pauseAudio: () {},
+        playSentence: (_, _) async => SentencePlaybackResult.completed,
+        startRecording:
+            ({
+              required promptId,
+              required referenceText,
+              required maxDuration,
+              referenceDuration,
+            }) {
+              recordings.add((max: maxDuration, reference: referenceDuration));
+            },
+        cancelRecording: () async {},
+        stopAndEvaluate: ({required referenceText}) async {},
+        clearRecording: () {},
+        setMaxRecordingDuration: (_) {},
+        hasDetectedSpeech: () => false,
+      ),
+    );
+    engine.prepare(
+      sentences: [
+        Sentence(
+          index: 0,
+          text: 'A slower sentence.',
+          startTime: Duration.zero,
+          endTime: const Duration(seconds: 4),
+        ),
+      ],
+      config: RepeatFlowConfig(
+        audioItemId: 'audio-1',
+        getRepeatCount: (_) => 1,
+        getIntervalDuration: (_) => Duration.zero,
+        isManualMode: () => false,
+        playbackSpeed: () => 0.8,
+      ),
+    );
+
+    await engine.startPlaying();
+
+    // 4s ÷ 0.8 = 5s；最大时长 = 5s × 2.5 + 5s = 17.5s
+    expect(recordings, hasLength(1));
+    expect(recordings.single.reference, const Duration(seconds: 5));
+    expect(recordings.single.max, const Duration(milliseconds: 17500));
+    engine.dispose();
+  });
 }