feat: 优化口语防重复问答、课程推进流转、键盘输入流畅度与竖屏锁定

- AI口语约束：在对话系统提示词与单轮指导中增加防重复问答约束，避免重复寒暄及索取已提供信息，根据历史自然向前推进
- 课程流转：修复多段课程学完后今日任务卡片流转下一课，及退出重进定位逻辑
- 竖屏锁定：在 Flutter、Android 及 iOS 平台配置仅支持竖屏显示
- 对话交互：优化对话界面文本输入重绘与词汇查询，解决键盘输入卡顿
- 测试用例：补充并更新单轮约束、状态流转与返回键退出测试，212项测试全绿

kouyu_english/lib/features/dialogue/dialogue_flow.dart

@@ -682,18 +682,20 @@ class _DialoguePageState extends State<DialoguePage>
       child: SpacedColumn(
         children: [
           Eyebrow('目标：${script.goal}'),
-          Container(
-            constraints: const BoxConstraints(minHeight: 250),
-            child: ListView.separated(
-              shrinkWrap: true,
-              physics: const NeverScrollableScrollPhysics(),
-              itemCount: turns.length,
-              separatorBuilder: (_, _) => const SizedBox(height: 10),
-              itemBuilder: (context, index) => _TurnBubble(
-                turn: turns[index],
-                state: widget.state,
-                showTranslation: _shownTranslations.contains(index),
-                onToggleTranslation: () => _toggleTurnTranslation(index),
+          RepaintBoundary(
+            child: Container(
+              constraints: const BoxConstraints(minHeight: 250),
+              child: ListView.separated(
+                shrinkWrap: true,
+                physics: const NeverScrollableScrollPhysics(),
+                itemCount: turns.length,
+                separatorBuilder: (_, _) => const SizedBox(height: 10),
+                itemBuilder: (context, index) => _TurnBubble(
+                  turn: turns[index],
+                  state: widget.state,
+                  showTranslation: _shownTranslations.contains(index),
+                  onToggleTranslation: () => _toggleTurnTranslation(index),
+                ),
               ),
             ),
           ),
@@ -750,13 +752,22 @@ class _DialoguePageState extends State<DialoguePage>
               ),
             TextField(
               controller: controller,
-              onChanged: (value) => setState(() {
-                if (usedVoice && value != lastTranscript) {
-                  transcriptEdited = true;
+              onChanged: (value) {
+                final needResetVoice =
+                    usedVoice &&
+                    value != lastTranscript &&
+                    !transcriptEdited;
+                final needClearAi = aiCheck != null || aiCheckError != null;
+                if (needResetVoice || needClearAi) {
+                  setState(() {
+                    if (needResetVoice) transcriptEdited = true;
+                    if (needClearAi) {
+                      aiCheck = null;
+                      aiCheckError = null;
+                    }
+                  });
                 }
-                aiCheck = null;
-                aiCheckError = null;
-              }),
+              },
               onSubmitted: (_) => send(),
               decoration: InputDecoration(
                 hintText: '输入你的英文回答',
@@ -785,21 +796,27 @@ class _DialoguePageState extends State<DialoguePage>
                 border: const OutlineInputBorder(),
               ),
             ),
-            OutlinedButton.icon(
-              onPressed:
-                  controller.text.trim().isEmpty ||
-                      checkingWithAi ||
-                      waitingForReply
-                  ? null
-                  : _checkWithAi,
-              icon: checkingWithAi
-                  ? const SizedBox(
-                      width: 16,
-                      height: 16,
-                      child: CircularProgressIndicator(strokeWidth: 2),
-                    )
-                  : const Icon(Icons.spellcheck),
-              label: Text(checkingWithAi ? '正在检查…' : '发送前 AI 检查语法和拼写（可选）'),
+            ValueListenableBuilder<TextEditingValue>(
+              valueListenable: controller,
+              builder: (context, value, _) {
+                final canCheck =
+                    value.text.trim().isNotEmpty &&
+                    !checkingWithAi &&
+                    !waitingForReply;
+                return OutlinedButton.icon(
+                  onPressed: canCheck ? _checkWithAi : null,
+                  icon: checkingWithAi
+                      ? const SizedBox(
+                          width: 16,
+                          height: 16,
+                          child: CircularProgressIndicator(strokeWidth: 2),
+                        )
+                      : const Icon(Icons.spellcheck),
+                  label: Text(
+                    checkingWithAi ? '正在检查…' : '发送前 AI 检查语法和拼写（可选）',
+                  ),
+                );
+              },
             ),
             if (aiCheck != null)
               SectionCard(

kouyu_english/lib/features/home/today_task_card.dart

@@ -49,7 +49,15 @@ class TodayTaskCard extends StatelessWidget {
   }
 
   _TodayTask _todayTask() {
-    final lesson = lessonById(state.activeLessonId);
+    var lessonId = state.activeLessonId;
+    if (state.completedLessonIds.contains(lessonId)) {
+      final next = state.nextIncompleteLessonId;
+      if (next != null) {
+        lessonId = next;
+      }
+    }
+    final lesson = lessonById(lessonId);
+
     if (state.hasResumableLessonDialogue) {
       return _TodayTask(
         label: '未完成',
@@ -75,17 +83,39 @@ class TodayTaskCard extends StatelessWidget {
     }
     // A0 课程学完、尚未通过阶段评估时，先巩固再评估；通过后回到下一课。
     if (state.a0LessonsComplete && !state.a0Passed) return _stageTask();
+
+    if (state.allLessonsComplete) {
+      return _TodayTask(
+        label: '已学完',
+        title: '所有课程已完成',
+        note: '你已学完全部课程内容！建议保持日常到期复习或自由情境对话。',
+        action: '去复习',
+        minutes: '10 分钟',
+        onPressed: onStartReview,
+      );
+    }
+
     final segments = lesson.segments.length;
-    final segment = state.activeSegmentIndexFor(lesson.id) + 1;
+    final segmentIndex = state.activeSegmentIndexFor(lesson.id);
+    final segment = segmentIndex + 1;
+    final isSegmentResuming = segments > 1 && segmentIndex > 0;
+
     return _TodayTask(
-      label: '今日新课',
+      label: isSegmentResuming ? '继续课程' : '今日新课',
       title:
           '第 ${lesson.number} 课 · ${lesson.title}'
           '${segments > 1 ? ' · 第 $segment/$segments 段' : ''}',
-      note: '预热词汇 → 听说读写 → 对话 → 独立尝试',
-      action: '开始今天的学习',
+      note: isSegmentResuming
+          ? '第 $segmentIndex 段已学完；继续本课下一段情境训练。'
+          : '预热词汇 → 听说读写 → 对话 → 独立尝试',
+      action: isSegmentResuming ? '继续学习第 $segment 段' : '开始今天的学习',
       minutes: '12 分钟',
-      onPressed: onStartLesson,
+      onPressed: () {
+        if (state.activeLessonId != lesson.id) {
+          state.openLesson(lesson.id);
+        }
+        onStartLesson();
+      },
     );
   }
 

kouyu_english/lib/features/lesson/lesson_flow.dart

@@ -64,6 +64,7 @@ class _LessonFlowState extends State<LessonFlow> {
   @override
   void initState() {
     super.initState();
+    widget.state.addListener(_onStateChange);
     writingController.text = widget.state.lessonWritingDraft;
     independentController.text = widget.state.independentAttemptDraft;
     previewIndex = widget.state.previewIndex
@@ -73,11 +74,16 @@ class _LessonFlowState extends State<LessonFlow> {
 
   @override
   void dispose() {
+    widget.state.removeListener(_onStateChange);
     writingController.dispose();
     independentController.dispose();
     super.dispose();
   }
 
+  void _onStateChange() {
+    if (mounted) setState(() {});
+  }
+
   @override
   Widget build(BuildContext context) {
     final lesson = lessonById(widget.state.activeLessonId);
@@ -230,19 +236,23 @@ class _LessonFlowState extends State<LessonFlow> {
               widget.state.activeSegmentIndexFor(lesson.id) ==
               lesson.segments.length - 1,
           nextSegmentNumber: widget.state.activeSegmentIndexFor(lesson.id) + 2,
-          onFinish: () {
-            widget.state.finishCurrentLessonSegment();
-            widget.onFinish();
-          },
+          onFinish: _finishOrExit,
         );
     }
     return _LessonScope(
       title:
           '第 ${lesson.number} 课 · ${lesson.title} · 第 ${widget.state.activeSegmentIndexFor(lesson.id) + 1}/${lesson.segments.length} 段',
-      onExit: widget.onFinish,
+      onExit: _finishOrExit,
       child: content,
     );
   }
+
+  void _finishOrExit() {
+    if (widget.state.lessonStep == LessonStep.complete) {
+      widget.state.finishCurrentLessonSegment();
+    }
+    widget.onFinish();
+  }
 }
 
 class _LessonScaffold extends StatelessWidget {

kouyu_english/lib/features/shell/learning_shell.dart

@@ -71,6 +71,9 @@ class _LearningShellState extends State<LearningShell> {
   void handleBack() {
     switch (route) {
       case _ShellRoute.lesson:
+        if (widget.state.lessonStep == LessonStep.complete) {
+          widget.state.finishCurrentLessonSegment();
+        }
         showTab(tab);
       case _ShellRoute.dialogue:
         if (dialogueInLesson) {
@@ -99,66 +102,6 @@ class _LearningShellState extends State<LearningShell> {
 
   @override
   Widget build(BuildContext context) {
-    Widget body;
-    switch (route) {
-      case _ShellRoute.lesson:
-        body = LessonFlow(
-          // 换课或换段时重建，避免上一段的听力选择和播放状态沿用过来。
-          key: ValueKey(
-            '${widget.state.activeLessonId}-'
-            '${widget.state.activeSegmentIndexFor(widget.state.activeLessonId)}',
-          ),
-          state: widget.state,
-          onOpenDialogue: () => showDialogue(inLesson: true),
-          onFinish: () => showTab(tab),
-        );
-      case _ShellRoute.dialogue:
-        body = DialoguePage(
-          key: ValueKey(dialogueInLesson ? 'lesson' : 'scene-$sceneId'),
-          state: widget.state,
-          isLessonDialogue: dialogueInLesson,
-          sceneId: sceneId,
-          onFinished: (summary) {
-            if (dialogueInLesson) {
-              showLesson();
-            } else if (summary != null) {
-              showSummary(summary);
-            } else {
-              handleBack();
-            }
-          },
-        );
-      case _ShellRoute.summary:
-        body = DialogueSummaryPage(
-          summary: dialogueSummary!,
-          onHome: () => showTab(AppTab.learn),
-          onLesson: showLesson,
-          onRetry: () => showDialogue(scene: sceneId),
-          onBack: () => showTab(tab),
-        );
-      case _ShellRoute.adaptiveLesson:
-        body = AdaptiveLessonPage(
-          state: widget.state,
-          onFinished: () => showTab(AppTab.review),
-        );
-      case _ShellRoute.assessment:
-        body = AssessmentPage(
-          state: widget.state,
-          pack: assessmentPack!,
-          onFinished: () => showTab(AppTab.profile),
-          onStartReplacement: showAssessment,
-        );
-      case _ShellRoute.assessmentPreparation:
-        body = AssessmentPreparationPage(
-          state: widget.state,
-          pack: assessmentPack!,
-          onStart: startAssessment,
-          onBack: () => showTab(AppTab.profile),
-        );
-      case _ShellRoute.tab:
-        body = _tabContent();
-    }
-
     return PopScope(
       canPop: route == _ShellRoute.tab && tab == AppTab.learn,
       onPopInvokedWithResult: (didPop, _) {
@@ -168,8 +111,69 @@ class _LearningShellState extends State<LearningShell> {
       },
       child: AnimatedBuilder(
         animation: widget.state,
-        builder: (context, _) => Scaffold(
-          body: body,
+        builder: (context, _) {
+          final Widget body;
+          switch (route) {
+            case _ShellRoute.lesson:
+              body = LessonFlow(
+                // 换课或换段时重建，避免上一段的听力选择和播放状态沿用过来。
+                key: ValueKey(
+                  '${widget.state.activeLessonId}-'
+                  '${widget.state.activeSegmentIndexFor(widget.state.activeLessonId)}',
+                ),
+                state: widget.state,
+                onOpenDialogue: () => showDialogue(inLesson: true),
+                onFinish: () => showTab(tab),
+              );
+            case _ShellRoute.dialogue:
+              body = DialoguePage(
+                key: ValueKey(dialogueInLesson ? 'lesson' : 'scene-$sceneId'),
+                state: widget.state,
+                isLessonDialogue: dialogueInLesson,
+                sceneId: sceneId,
+                onFinished: (summary) {
+                  if (dialogueInLesson) {
+                    showLesson();
+                  } else if (summary != null) {
+                    showSummary(summary);
+                  } else {
+                    handleBack();
+                  }
+                },
+              );
+            case _ShellRoute.summary:
+              body = DialogueSummaryPage(
+                summary: dialogueSummary!,
+                onHome: () => showTab(AppTab.learn),
+                onLesson: showLesson,
+                onRetry: () => showDialogue(scene: sceneId),
+                onBack: () => showTab(tab),
+              );
+            case _ShellRoute.adaptiveLesson:
+              body = AdaptiveLessonPage(
+                state: widget.state,
+                onFinished: () => showTab(AppTab.review),
+              );
+            case _ShellRoute.assessment:
+              body = AssessmentPage(
+                state: widget.state,
+                pack: assessmentPack!,
+                onFinished: () => showTab(AppTab.profile),
+                onStartReplacement: showAssessment,
+              );
+            case _ShellRoute.assessmentPreparation:
+              body = AssessmentPreparationPage(
+                state: widget.state,
+                pack: assessmentPack!,
+                onStart: startAssessment,
+                onBack: () => showTab(AppTab.profile),
+              );
+            case _ShellRoute.tab:
+              body = _tabContent();
+          }
+
+          return Scaffold(
+            body: body,
           bottomNavigationBar: route == _ShellRoute.tab
               ? NavigationBar(
                   selectedIndex: tab.index,
@@ -201,7 +205,8 @@ class _LearningShellState extends State<LearningShell> {
                   ],
                 )
               : null,
-        ),
+          );
+        },
       ),
     );
   }
@@ -211,7 +216,14 @@ class _LearningShellState extends State<LearningShell> {
       case AppTab.learn:
         return HomePage(
           state: widget.state,
-          onStartLesson: showLesson,
+          onStartLesson: () {
+            if (widget.state.completedLessonIds
+                .contains(widget.state.activeLessonId)) {
+              final next = widget.state.nextIncompleteLessonId;
+              if (next != null) widget.state.openLesson(next);
+            }
+            showLesson();
+          },
           onOpenLesson: (id) {
             widget.state.openLesson(id);
             showLesson();