feat: 独立词库、三向认词与当日快闪复习

## 独立词库

理解词原先只能跟着课程单元走，学完 A0 十课词汇量只增加约 22 个实词，
不足以解决"记不住单词"。新增一份独立词库 assets/words/wordbank.json
（2748 词，A1–B1），挂进 receptiveWordRegistry 的合成单元 bank-A1/A2/B1，
完全复用理解词已有的状态机，不依赖课程进度，第一天就能用。

数据来源、许可与合成规则记在 tool/words/DATA-NOTE.md：CEFR-J 定等级、
公开词书提供音标、AI 重写全部释义并生成例句、OpenSubtitles 提供口语词频。
词书部分为 CC BY-NC-SA 4.0 且上游权利不明，仅供个人非商用；
若要分发或上架，须替换音标那一列。

## 背单词机制

- 间隔阶梯 1/3/7/15/30/60/120 天，连续答对上一级，答错回第一级。
  原先首次答对后要等 7 天才复习，正是"第二天就忘"的成因。
- 每日新词上限（10 分钟 8 个 / 20 分钟 15 个 / 30 分钟 20 个）。
  阶梯第一级是次日，今天引入的新词就是明天的工作量。
- 新词按口语频率发放，不再按字母序 —— A1 从 a.m./ability 变成 no/not/know/just。
- 三个方向按层级轮转：看词（英→中）→ 听词（音→中）→ 想词（中→英）。
  想词题仍是选择题，不要求产出，理解词定位不变，不进升级分母。
- 单词页独立成 tab，首页今日任务卡下方给一张认词入口卡。

## 用法对照

课程 JSON 增加 usage 字段（when/reply/swap/confuse）：一个句型用在什么场合、
对方通常怎么答、还能怎么说、跟哪个学过的句型容易混。
知道 How are you? 的意思，不等于知道它不是用来问名字的。

## 复习流

- 当日快闪（recap）独立成队列，不占复习预算，也不计入积压。
- 只发放当日预算内的量，其余保持到期状态等下次，不悄悄丢弃或改期。
- 答错的项隔几题后回来，而不是立刻重问。

测试 296 通过，flutter analyze 干净。

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

kouyu_english/lib/features/home/home_page.dart

@@ -5,6 +5,7 @@ import '../../core/app_theme.dart';
 import '../../widgets/app_widgets.dart';
 import 'lesson_path.dart';
 import 'today_task_card.dart';
+import 'word_task_card.dart';
 
 /// 学习 tab：今天的任务在上，完整课程路径在下。
 class HomePage extends StatelessWidget {
@@ -17,6 +18,7 @@ class HomePage extends StatelessWidget {
     required this.onResumeLessonDialogue,
     required this.onStartReinforcement,
     required this.onOpenAssessment,
+    required this.onOpenWords,
   });
 
   final AppState state;
@@ -26,6 +28,7 @@ class HomePage extends StatelessWidget {
   final VoidCallback onResumeLessonDialogue;
   final VoidCallback onStartReinforcement;
   final ValueChanged<String> onOpenAssessment;
+  final VoidCallback onOpenWords;
 
   @override
   Widget build(BuildContext context) => AppPage(
@@ -41,6 +44,7 @@ class HomePage extends StatelessWidget {
           onStartReinforcement: onStartReinforcement,
           onOpenAssessment: onOpenAssessment,
         ),
+        WordTaskCard(state: state, onOpenWords: onOpenWords),
         LessonPath(state: state, onOpenLesson: onOpenLesson),
         const _FrameworkNote(),
       ],

kouyu_english/lib/features/home/today_task_card.dart

@@ -69,15 +69,29 @@ class TodayTaskCard extends StatelessWidget {
       );
     }
     if (state.reviewIsPrimary) {
-      final count = state.dueReviewCount;
+      final planned = state.todayReviewPlan.length;
+      final postponed = state.postponedReviewCount;
       return _TodayTask(
         label: '今日复习',
-        title: '先复习 $count 项',
-        note: state.reviewBacklog
+        title: '先复习 $planned 项',
+        note: postponed > 0
+            ? '今天的复习时间安排 $planned 项，其余 $postponed 项明天接着做，不会丢。'
+            : state.reviewBacklog
             ? '有积压项目；先花几分钟清掉到期复习，再开启新课。'
             : '之前练过的关键句，今天换个情境再用一次。',
         action: '开始复习',
-        minutes: '${(count * 2).clamp(2, 10)} 分钟',
+        minutes: '${(planned * 2).clamp(2, 10)} 分钟',
+        onPressed: onStartReview,
+      );
+    }
+    // 学完一段后隔一会儿再想起来一次，明天的第一次检查才不会从零开始。
+    if (state.dueRecaps.isNotEmpty) {
+      return _TodayTask(
+        label: '课后快闪',
+        title: '把刚学的 ${state.dueRecaps.length} 项再想一遍',
+        note: '趁还记得再提取一次，明天更容易想起来。答不出也不算错，不计检查点。',
+        action: '开始快闪',
+        minutes: '1 分钟',
         onPressed: onStartReview,
       );
     }

kouyu_english/lib/features/home/word_task_card.dart

@@ -0,0 +1,77 @@
+import 'package:flutter/material.dart';
+
+import '../../core/app_state.dart';
+import '../../core/app_theme.dart';
+import '../../widgets/app_widgets.dart';
+import '../words/words_page.dart';
+
+/// 首页的认词入口。
+///
+/// 认词跟今日任务是并行的，不是竞争关系：一个题几秒钟，不该去抢上面那张
+/// 今日任务卡的「今天最该做的一件事」。所以它单独占一行 —— 有题时是一张能
+/// 直接开始的卡，没题时缩成一行状态，但入口始终在。
+class WordTaskCard extends StatelessWidget {
+  const WordTaskCard({
+    super.key,
+    required this.state,
+    required this.onOpenWords,
+  });
+
+  final AppState state;
+  final VoidCallback onOpenWords;
+
+  @override
+  Widget build(BuildContext context) {
+    final planned = state.wordSessionPreviewSize;
+    if (planned == 0) return _restRow(context);
+    return SectionCard(
+      tint: AppColors.surfaceMuted,
+      onTap: onOpenWords,
+      child: SpacedColumn(
+        children: [
+          Row(
+            children: [
+              const Expanded(child: Eyebrow('认词')),
+              Text(
+                '${state.wordSessionMinutes(planned)} 分钟',
+                style: TextStyle(color: AppColors.muted),
+              ),
+            ],
+          ),
+          Text(
+            wordTaskHeadline(state),
+            style: const TextStyle(fontSize: 17, fontWeight: FontWeight.w600),
+          ),
+          Text(
+            '$planned 个题，听到、看到能认出来就行，不用会说。',
+            style: Theme.of(context).textTheme.bodyMedium,
+          ),
+          SecondaryButton(label: '开始认词', onPressed: onOpenWords),
+        ],
+      ),
+    );
+  }
+
+  Widget _restRow(BuildContext context) => SectionCard(
+    tint: AppColors.surfaceMuted,
+    onTap: onOpenWords,
+    child: Row(
+      children: [
+        Icon(Icons.abc_outlined, color: AppColors.muted, size: 20),
+        const SizedBox(width: 8),
+        Expanded(
+          child: Text(
+            state.newWordQuota > 0
+                ? '今天的词都过完了'
+                : '今天的新词学满 ${state.newWordsPerDay} 个了，明天继续',
+            style: Theme.of(context).textTheme.bodyMedium,
+          ),
+        ),
+        Text(
+          '认识 ${state.recognizedWordCount} · 熟悉 ${state.familiarWordCount}',
+          style: Theme.of(context).textTheme.bodySmall,
+        ),
+      ],
+    ),
+  );
+}

kouyu_english/lib/features/lesson/lesson_flow.dart

@@ -12,6 +12,7 @@ import '../../core/voice_service.dart';
 import '../../core/writing_feedback.dart';
 import '../../widgets/app_widgets.dart';
 import '../../widgets/lexicon_lookup.dart';
+import '../../widgets/usage_card.dart';
 import '../../widgets/voice_answer.dart';
 
 part 'steps/independent_step.dart';
@@ -148,6 +149,7 @@ class _LessonFlowState extends State<LessonFlow> {
       case LessonStep.speaking:
         content = _SpeakingStep(
           state: widget.state,
+          segmentId: segment.id,
           text: activity.speaking,
           tip: activity.speakingTip,
           keepRecording: widget.state.keepRecordings,

kouyu_english/lib/features/lesson/steps/preview_step.dart

@@ -47,6 +47,7 @@ class _PreviewStep extends StatelessWidget {
             ],
           ),
         ),
+        UsageCard(itemId: item.id, state: state),
         Wrap(
           spacing: 8,
           children: [ActionChip(label: const Text('查词'), onPressed: onLookup)],

kouyu_english/lib/features/lesson/steps/speaking_step.dart

@@ -3,11 +3,13 @@ part of '../lesson_flow.dart';
 class _SpeakingStep extends StatefulWidget {
   const _SpeakingStep({
     required this.state,
+    required this.segmentId,
     required this.text,
     this.tip = '',
     required this.keepRecording,
     required this.onContinue,
   });
+  final String segmentId;
   final String text;
   final String tip;
   final AppState state;
@@ -92,6 +94,7 @@ class _SpeakingStepState extends State<_SpeakingStep>
               style: TextStyle(color: AppColors.warmInk),
             ),
           ),
+        SegmentUsage(segmentId: widget.segmentId, state: widget.state),
         SecondaryButton(
           label: transcribing
               ? '正在 AI 识别发音…'

kouyu_english/lib/features/lesson/steps/writing_step.dart

@@ -91,6 +91,7 @@ class _WritingStepState extends State<_WritingStep> {
           tint: AppColors.surfaceMuted,
           child: Text('小提示：${grammarNoteForSegment(widget.segmentId)}'),
         ),
+        SegmentUsage(segmentId: widget.segmentId, state: widget.state),
         if (widget.showHelp)
           SectionCard(
             tint: AppColors.softGreen,

kouyu_english/lib/features/review/review_page.dart

@@ -11,6 +11,7 @@ import '../../core/courses/courses.dart';
 import '../../core/speech_compare.dart';
 import '../../core/voice_service.dart';
 import '../../widgets/app_widgets.dart';
+import '../../widgets/usage_card.dart';
 import '../../widgets/voice_answer.dart';
 
 class ReviewPage extends StatefulWidget {
@@ -50,6 +51,15 @@ class _ReviewPageState extends State<ReviewPage>
   ({String answer, String reference, String? audio, bool assisted})? lastResult;
   bool dictationPlayed = false;
 
+  /// Items whose recognition question has been answered in this session. The
+  /// gate is asked once per item; the production task follows immediately.
+  final Set<String> gateCleared = {};
+
+  /// The item whose contrast question is being shown after a miss, and the
+  /// option picked, if any. Set only while the remediation is on screen.
+  ReviewItem? contrastFor;
+  String? contrastPicked;
+
   @override
   AppState get voiceState => widget.state;
 
@@ -156,10 +166,204 @@ class _ReviewPageState extends State<ReviewPage>
     });
   }
 
+  /// Options for the recognition question: the meaning plus distractors from
+  /// the same unit. The answer's position is stable per item so it does not
+  /// move while the learner reads, but it is not always first.
+  List<String> _recognitionOptions(String id, String answer) {
+    final options = [answer, ...recognitionDistractors(id)];
+    final offset = id.hashCode.abs() % options.length;
+    return [...options.skip(offset), ...options.take(offset)];
+  }
+
+  void _answerGate(ReviewItem item, {required bool correct}) {
+    widget.state.recordRecognitionGate(item, correct: correct);
+    setState(() {
+      gateCleared.add(item.id);
+      // Being shown the meaning is help, so finishing the production step
+      // afterwards is recorded as assisted.
+      if (!correct) usedHelp = true;
+    });
+    if (!correct) {
+      ScaffoldMessenger.of(context).showSnackBar(
+        SnackBar(
+          content: Text(
+            '它的意思是：${coreRecognitionQuestion(item.id).answer}。下一步试着写出英文。',
+          ),
+        ),
+      );
+    }
+  }
+
+  /// Step one of an item's first checkpoint: hear or read it and pick what it
+  /// means. Recall of the English comes right after. Learning engine 3.1 puts
+  /// 「认识」 before 「可回忆」, so the day after a lesson opens with a question
+  /// the learner can answer instead of the hardest one.
+  Widget _recognitionView(ReviewItem item) {
+    final question = coreRecognitionQuestion(item.id);
+    final answer = question.answer;
+    final english = question.shown;
+    final audio = english;
+    return AppPage(
+      child: SpacedColumn(
+        children: [
+          Eyebrow('今天复习 · ${widget.state.reviewSession.length} 项待完成'),
+          Text(
+            '先认出来：它是什么意思？',
+            style: Theme.of(context).textTheme.headlineMedium,
+          ),
+          Text(
+            '第 1 步，共 2 步 · 认出来 → 说出来',
+            style: TextStyle(color: AppColors.green, fontSize: 13),
+          ),
+          SectionCard(
+            tint: AppColors.softGreen,
+            child: SpacedColumn(
+              children: [
+                Text(english, style: const TextStyle(fontSize: 22)),
+                Row(
+                    children: [
+                    IconButton.filled(
+                      tooltip: '播放',
+                      onPressed: () => _play(audio),
+                      icon: const Icon(Icons.volume_up_outlined),
+                    ),
+                    const SizedBox(width: 10),
+                    TextButton(
+                      onPressed: () => _play(audio, slow: true),
+                      child: const Text('慢速'),
+                    ),
+                  ],
+                ),
+              ],
+            ),
+          ),
+          for (final option in _recognitionOptions(item.id, answer))
+            SizedBox(
+              width: double.infinity,
+              child: OutlinedButton(
+                onPressed: () => _answerGate(item, correct: option == answer),
+                child: Align(
+                  alignment: Alignment.centerLeft,
+                  child: Padding(
+                    padding: const EdgeInsets.symmetric(vertical: 6),
+                    child: Text(option, style: const TextStyle(fontSize: 16)),
+                  ),
+                ),
+              ),
+            ),
+          TextButton(
+            onPressed: () => _answerGate(item, correct: false),
+            child: const Text('不认识'),
+          ),
+          Text(
+            '选错或选「不认识」都不算答错，会直接告诉你意思，再一起练说出来。',
+            style: TextStyle(fontSize: 12, color: AppColors.muted),
+          ),
+        ],
+      ),
+    );
+  }
+
+  void _reportMiss(ReviewItem item) {
+    widget.state.reportReviewFailure(item);
+    // Being told the answer is the moment to say what the item is for. A
+    // learner who could not produce `What's your name?` often knows the words
+    // and not the situation.
+    if (coreContrastQuestion(item.id, isTaught: widget.state.mastery.containsKey) != null) {
+      setState(() {
+        _resetAnswer();
+        contrastFor = item;
+        contrastPicked = null;
+      });
+      return;
+    }
+    setState(_resetAnswer);
+  }
+
+  void _answerContrast(ReviewItem item, String picked, String answer) {
+    widget.state.recordContrastAnswer(item, correct: picked == answer);
+    setState(() => contrastPicked = picked);
+  }
+
+  /// The remediation after a miss: the usage note, then the situation with the
+  /// taught sentences to choose between. It is teaching, not a checkpoint —
+  /// the miss is already recorded and answering here cannot undo it.
+  Widget _contrastView(ReviewItem item) {
+    final question = coreContrastQuestion(
+      item.id,
+      isTaught: widget.state.mastery.containsKey,
+    )!;
+    final picked = contrastPicked;
+    return AppPage(
+      child: SpacedColumn(
+        children: [
+          const Eyebrow('先弄清楚什么时候用'),
+          Text(
+            '这句话用在这种情况：',
+            style: Theme.of(context).textTheme.headlineMedium,
+          ),
+          UsageCard(itemId: item.id, state: widget.state),
+          SectionCard(
+            tint: AppColors.surfaceMuted,
+            child: Text(question.situation, style: const TextStyle(fontSize: 17)),
+          ),
+          const Text('这时候该说哪一句？'),
+          for (final option in question.options)
+            SizedBox(
+              width: double.infinity,
+              child: OutlinedButton(
+                onPressed: picked == null
+                    ? () => _answerContrast(item, option, question.answer)
+                    : null,
+                style: picked == null
+                    ? null
+                    : OutlinedButton.styleFrom(
+                        backgroundColor: option == question.answer
+                            ? AppColors.softGreen
+                            : null,
+                      ),
+                child: Align(
+                  alignment: Alignment.centerLeft,
+                  child: Padding(
+                    padding: const EdgeInsets.symmetric(vertical: 6),
+                    child: Text(option, style: const TextStyle(fontSize: 16)),
+                  ),
+                ),
+              ),
+            ),
+          if (picked != null) ...[
+            SectionCard(
+              tint: picked == question.answer
+                  ? AppColors.softGreen
+                  : AppColors.warm,
+              child: Text(
+                picked == question.answer
+                    ? '对，就是这句。${question.note}'
+                    : '这里要说 ${question.answer}。${question.note}',
+                style: TextStyle(color: AppColors.warmInk, height: 1.45),
+              ),
+            ),
+            PrimaryButton(
+              label: '继续复习',
+              onPressed: () => setState(() {
+                contrastFor = null;
+                contrastPicked = null;
+              }),
+            ),
+          ],
+          Text(
+            '这一步不算检查点，也不会影响刚才那道题的结果。',
+            style: TextStyle(fontSize: 12, color: AppColors.muted),
+          ),
+        ],
+      ),
+    );
+  }
+
   Widget _resultView(
     ({String answer, String reference, String? audio, bool assisted}) result,
   ) {
-    final remaining = widget.state.dueReviews.length;
+    final remaining = widget.state.reviewSession.length;
     return AppPage(
       child: SpacedColumn(
         children: [
@@ -311,11 +515,12 @@ class _ReviewPageState extends State<ReviewPage>
 
   @override
   Widget build(BuildContext context) {
+    if (contrastFor case final item?) return _contrastView(item);
     if (lastResult case final result?) return _resultView(result);
-    final item = widget.state.dueReviews.isEmpty
-        ? null
-        : widget.state.dueReviews.first;
+    final session = widget.state.reviewSession;
+    final item = session.isEmpty ? null : session.first;
     if (item == null) {
+      final postponed = widget.state.postponedReviewCount;
       return AppPage(
         child: SpacedColumn(
           children: [
@@ -324,12 +529,20 @@ class _ReviewPageState extends State<ReviewPage>
               '到期项目已安排下次复练。',
               style: Theme.of(context).textTheme.headlineMedium,
             ),
-            const Text('记住不是一次答对就结束；系统会在不同间隔再次确认你仍能用出来。'),
+            Text(
+              postponed > 0
+                  ? '今天的复习时间用完了，还有 $postponed 项到期，明天接着做，没有被丢掉。'
+                  : '记住不是一次答对就结束；系统会在不同间隔再次确认你仍能用出来。',
+            ),
             PrimaryButton(label: '回到首页', onPressed: widget.onFinished),
           ],
         ),
       );
     }
+    if (widget.state.needsRecognitionGate(item) &&
+        !gateCleared.contains(item.id)) {
+      return _recognitionView(item);
+    }
     final dictation = item.skill == dictationSkill
         ? coreDictationSentences[item.id]
         : null;
@@ -337,17 +550,33 @@ class _ReviewPageState extends State<ReviewPage>
     final audioText = reviewAudioText(item.id, item.target);
     final checkpoint =
         widget.state.mastery[item.id]?.checkpoint ?? item.successfulReviews;
-    final checkpointLabel = checkpoint >= 4
+    final isRecap = item.kind == ReviewKind.recap;
+    final checkpointLabel = isRecap
+        ? '不计检查点 · 只是趁热再想一遍'
+        : checkpoint >= 4
         ? '30 天抽查'
         : '第 ${checkpoint + 1} / 4 个间隔检查点';
     return AppPage(
       child: SpacedColumn(
         children: [
-          Eyebrow('今天复习 · ${widget.state.dueReviewCount} 项待完成'),
+          Eyebrow(
+            isRecap
+                ? '再想一遍 · 还有 ${widget.state.reviewSession.length} 项'
+                : '今天复习 · ${widget.state.reviewSession.length} 项待完成',
+          ),
           Text(
-            dictation != null ? '听一听，写下来。' : '不看答案，试着回答。',
+            dictation != null
+                ? '听一听，写下来。'
+                : isRecap
+                ? '刚学过的，现在还想得起来吗？'
+                : '不看答案，试着回答。',
             style: Theme.of(context).textTheme.headlineMedium,
           ),
+          if (isRecap)
+            Text(
+              '答不出也不算错，看一眼答案就好——这一次只是帮你记住，真正的检查在明天。',
+              style: TextStyle(fontSize: 12, color: AppColors.muted),
+            ),
           Text(
             '目标技能：${item.skill}',
             style: Theme.of(context).textTheme.bodyMedium,
@@ -465,10 +694,7 @@ class _ReviewPageState extends State<ReviewPage>
               ),
               ActionChip(
                 label: const Text('暂时想不起来'),
-                onPressed: () {
-                  widget.state.reportReviewFailure(item);
-                  setState(_resetAnswer);
-                },
+                onPressed: () => _reportMiss(item),
               ),
               ActionChip(
                 label: Text(generatingVariant ? '正在生成…' : '生成变式'),
@@ -509,6 +735,7 @@ class _ReviewPageState extends State<ReviewPage>
                       icon: const Icon(Icons.volume_up_outlined),
                       label: Text('听示范：$audioText'),
                     ),
+                  UsageCard(itemId: item.id, state: widget.state),
                 ],
               ),
             ),

kouyu_english/lib/features/shell/learning_shell.dart

@@ -10,6 +10,7 @@ import "../home/home_page.dart";
 import "../lesson/lesson_flow.dart";
 import "../profile/profile_page.dart";
 import "../review/review_page.dart";
+import "../words/words_page.dart";
 
 class LearningShell extends StatefulWidget {
   const LearningShell({super.key, required this.state});
@@ -197,6 +198,11 @@ class _LearningShellState extends State<LearningShell> {
                       selectedIcon: Icon(Icons.refresh),
                       label: "复习",
                     ),
+                    NavigationDestination(
+                      icon: Icon(Icons.abc_outlined),
+                      selectedIcon: Icon(Icons.abc),
+                      label: "单词",
+                    ),
                     NavigationDestination(
                       icon: Icon(Icons.person_outline),
                       selectedIcon: Icon(Icons.person),
@@ -240,6 +246,7 @@ class _LearningShellState extends State<LearningShell> {
                 .firstOrNull;
             if (pack != null) showAssessment(pack);
           },
+          onOpenWords: () => showTab(AppTab.words),
         );
       case AppTab.dialogue:
         return DialogueScenePage(
@@ -252,6 +259,8 @@ class _LearningShellState extends State<LearningShell> {
           onFinished: () => showTab(AppTab.learn),
           onOpenAdaptiveLesson: showAdaptiveLesson,
         );
+      case AppTab.words:
+        return WordsPage(state: widget.state);
       case AppTab.profile:
         return ProfilePage(
           state: widget.state,

kouyu_english/lib/features/words/words_page.dart

@@ -0,0 +1,363 @@
+import 'package:flutter/material.dart';
+
+import '../../core/app_state.dart';
+import '../../core/app_theme.dart';
+import '../../core/courses/courses.dart';
+import '../../core/models.dart';
+import '../../core/voice_service.dart';
+import '../../widgets/app_widgets.dart';
+
+/// What the round of recognition is about right now. The home card and this
+/// page share it so the two never describe today's words differently.
+String wordTaskHeadline(AppState state) {
+  final due = state.dueWords.length;
+  if (due > 0) return '今天有 $due 个词该过一遍';
+  final unasked = state.unaskedWords.length;
+  if (unasked > 0) return '有 $unasked 个新学的词还没问过';
+  return '今天还能学 ${state.newWordQuota} 个新词';
+}
+
+/// The word list the learner can open on its own (learning engine 3.5).
+///
+/// Words are never asked to be produced here: the only task is a 5–10 second
+/// recognition question, and the rest of the page is just what has been met.
+class WordsPage extends StatefulWidget {
+  const WordsPage({super.key, required this.state});
+
+  final AppState state;
+
+  @override
+  State<WordsPage> createState() => _WordsPageState();
+}
+
+class _WordsPageState extends State<WordsPage> {
+  List<WordQuestion>? quiz;
+  int index = 0;
+  String? picked;
+  int right = 0;
+
+  void _startQuiz() {
+    final plan = widget.state.wordSession();
+    if (plan.isEmpty) return;
+    setState(() {
+      quiz = plan;
+      index = 0;
+      picked = null;
+      right = 0;
+    });
+    _playIfHeard(plan.first);
+  }
+
+  /// A listening question plays itself: the learner should not have to find a
+  /// button before the question has even been asked.
+  void _playIfHeard(WordQuestion question) {
+    if (question.mode != WordAskMode.listen) return;
+    VoiceService.instance.speak(wordEnglish(question.id));
+  }
+
+  void _answer(WordQuestion question, String option) {
+    final correct = option == question.answer;
+    widget.state.recordWordRecognition(question.id, correct: correct);
+    setState(() {
+      picked = option;
+      if (correct) right += 1;
+    });
+  }
+
+  void _next() {
+    final last = index + 1 >= quiz!.length;
+    setState(() {
+      if (last) {
+        quiz = null;
+      } else {
+        index += 1;
+      }
+      picked = null;
+    });
+    if (!last) _playIfHeard(quiz![index]);
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    if (quiz case final questions?) return _quizView(questions[index]);
+    return _listView();
+  }
+
+  Widget _quizView(WordQuestion question) {
+    final answered = picked != null;
+    final english = wordEnglish(question.id);
+    final ipa = wordIpa(question.id);
+    // Before the answer each way round gives a different clue; after it all
+    // three land on the spelling, which is what the question was for.
+    // Withholding it earlier is the question: a heard word shown spelled is
+    // a reading question, and a meaning shown next to its word is no question
+    // at all.
+    final prompt = switch (question.mode) {
+      WordAskMode.read => english,
+      WordAskMode.listen => answered ? english : '· · ·',
+      WordAskMode.recall => answered ? english : question.shown,
+    };
+    // Speaking the word before a recall answer would just read it out.
+    final canSpeak = answered || question.mode != WordAskMode.recall;
+    return AppPage(
+      child: SpacedColumn(
+        children: [
+          Eyebrow(
+            '${switch (question.mode) {
+              WordAskMode.read => '认词',
+              WordAskMode.listen => '听词',
+              WordAskMode.recall => '想词',
+            }} · ${index + 1} / ${quiz!.length}',
+          ),
+          Row(
+            children: [
+              Expanded(
+                child: Column(
+                  crossAxisAlignment: CrossAxisAlignment.start,
+                  children: [
+                    Text(
+                      prompt,
+                      style: Theme.of(context).textTheme.headlineMedium,
+                    ),
+                    if (answered &&
+                        ipa.isNotEmpty &&
+                        question.mode != WordAskMode.read)
+                      Text(ipa, style: Theme.of(context).textTheme.bodyMedium),
+                  ],
+                ),
+              ),
+              if (canSpeak)
+                IconButton(
+                  icon: Icon(
+                    question.mode == WordAskMode.listen
+                        ? Icons.replay_outlined
+                        : Icons.volume_up_outlined,
+                  ),
+                  tooltip: question.mode == WordAskMode.listen ? '再听一遍' : null,
+                  onPressed: () => VoiceService.instance.speak(english),
+                ),
+            ],
+          ),
+          Text(switch (question.mode) {
+            WordAskMode.read => '它是什么意思？只要认出来就行，不用会说。',
+            WordAskMode.listen => '听到的是哪个意思？听不清可以再听一遍。',
+            WordAskMode.recall => '哪个词是这个意思？认出来就行，不用自己拼。',
+          }),
+          for (final option in question.options)
+            SizedBox(
+              width: double.infinity,
+              child: OutlinedButton(
+                onPressed: answered ? null : () => _answer(question, option),
+                style: !answered || option != question.answer
+                    ? null
+                    : OutlinedButton.styleFrom(
+                        backgroundColor: AppColors.softGreen,
+                      ),
+                child: Align(
+                  alignment: Alignment.centerLeft,
+                  child: Padding(
+                    padding: const EdgeInsets.symmetric(vertical: 6),
+                    child: Text(option, style: const TextStyle(fontSize: 16)),
+                  ),
+                ),
+              ),
+            ),
+          if (answered) ...[
+            SectionCard(
+              tint: picked == question.answer
+                  ? AppColors.softGreen
+                  : AppColors.warm,
+              child: SpacedColumn(
+                children: [
+                  Text(
+                    picked == question.answer
+                        ? '对了。'
+                        : question.mode == WordAskMode.recall
+                        ? '「${question.shown}」是 $english，明天再问你一次。'
+                        : '$english 是「${question.answer}」，明天再问你一次。',
+                    style: TextStyle(color: AppColors.warmInk, height: 1.45),
+                  ),
+                  // The sentence is the point of the feedback: a gloss alone is
+                  // what did not stick the first time.
+                  if (WordBank.instance.exampleOf(question.id) case final sample?) ...[
+                    Text(
+                      sample.en,
+                      style: TextStyle(
+                        color: AppColors.warmInk,
+                        fontSize: 16,
+                        height: 1.45,
+                      ),
+                    ),
+                    if (sample.zh.isNotEmpty)
+                      Text(
+                        sample.zh,
+                        style: Theme.of(context).textTheme.bodyMedium,
+                      ),
+                  ],
+                  if (WordBank.instance.moreSenses(question.id) case final more
+                      when more.isNotEmpty)
+                    Text(
+                      '也有「$more」的意思。',
+                      style: Theme.of(context).textTheme.bodySmall,
+                    ),
+                ],
+              ),
+            ),
+            PrimaryButton(
+              label: index + 1 >= quiz!.length ? '做完了' : '下一个',
+              onPressed: _next,
+            ),
+          ],
+          TextButton(
+            onPressed: () => setState(() {
+              quiz = null;
+              picked = null;
+            }),
+            child: const Text('先不做了'),
+          ),
+        ],
+      ),
+    );
+  }
+
+  Widget _listView() {
+    final state = widget.state;
+    final shaky = state.shakyWords;
+    final grouped = state.wordsByUnit;
+    final waiting = state.unstartedBankWordCount;
+    final quota = state.newWordQuota;
+    final planned = state.wordSessionPreviewSize;
+    return AppPage(
+      child: SpacedColumn(
+        children: [
+          const Eyebrow('学过的词'),
+          Text(
+            grouped.isEmpty
+                ? '还没有学过的词'
+                : '认识 ${state.recognizedWordCount} · 熟悉 ${state.familiarWordCount}',
+            style: Theme.of(context).textTheme.headlineMedium,
+          ),
+          const Text('这些词只要听到、看到能认出来就够了，不用背着写出来。'),
+          if (planned > 0)
+            SectionCard(
+              tint: AppColors.softGreen,
+              child: SpacedColumn(
+                children: [
+                  Text(
+                    wordTaskHeadline(state),
+                    style: const TextStyle(fontSize: 17),
+                  ),
+                  Text(
+                    '$planned 个题，一个题几秒钟。',
+                    style: Theme.of(context).textTheme.bodyMedium,
+                  ),
+                  PrimaryButton(label: '开始认词', onPressed: _startQuiz),
+                ],
+              ),
+            )
+          else if (grouped.isNotEmpty)
+            SectionCard(
+              tint: AppColors.surfaceMuted,
+              child: Text(
+                quota > 0
+                    ? '今天的词都过完了，剩下的等到期再问。'
+                    : '今天的新词学满 ${state.newWordsPerDay} 个了，到期的也都过完了。'
+                          '明天它们会回来找你。',
+              ),
+            ),
+          if (waiting > 0)
+            Text(
+              quota > 0
+                  ? '词库里还有 $waiting 个词没开始，今天还能学 $quota 个。'
+                  : '词库里还有 $waiting 个词没开始，明天继续。',
+              style: Theme.of(context).textTheme.bodySmall,
+            ),
+          if (shaky.isNotEmpty) ...[
+            const Eyebrow('没记住的'),
+            SectionCard(
+              tint: AppColors.warm,
+              child: SpacedColumn(
+                children: [
+                  for (final id in shaky.take(8)) _WordRow(id: id, state: state),
+                ],
+              ),
+            ),
+          ],
+          for (final entry in grouped.entries) ...[
+            Eyebrow(_unitTitle(entry.key)),
+            SectionCard(
+              tint: AppColors.surfaceMuted,
+              child: SpacedColumn(
+                children: [
+                  for (final id in entry.value.take(_groupLimit))
+                    _WordRow(id: id, state: state),
+                  if (entry.value.length > _groupLimit)
+                    Text(
+                      '还有 ${entry.value.length - _groupLimit} 个',
+                      style: Theme.of(context).textTheme.bodySmall,
+                    ),
+                ],
+              ),
+            ),
+          ],
+        ],
+      ),
+    );
+  }
+
+  /// A unit group is a reminder of what has been met, not a dictionary, so it
+  /// stops before the bank turns it into an endless scroll.
+  static const _groupLimit = 30;
+
+  String _unitTitle(String unit) {
+    if (unit.isEmpty) return '查词收藏';
+    if (WordBank.isBankUnit(unit)) return '词库 · ${WordBank.levelOfUnit(unit)}';
+    final lesson = allLessons.where((item) => item.id == unit);
+    return lesson.isEmpty ? unit : lesson.first.title;
+  }
+}
+
+class _WordRow extends StatelessWidget {
+  const _WordRow({required this.id, required this.state});
+
+  final String id;
+  final AppState state;
+
+  @override
+  Widget build(BuildContext context) {
+    final status = state.wordStatus(id);
+    return Row(
+      children: [
+        Expanded(
+          child: Column(
+            crossAxisAlignment: CrossAxisAlignment.start,
+            children: [
+              Text(
+                wordEnglish(id),
+                style: const TextStyle(fontSize: 16, fontWeight: FontWeight.w600),
+              ),
+              Text(
+                wordIpa(id).isEmpty
+                    ? wordMeaning(id)
+                    : '${wordIpa(id)}  ${wordMeaning(id)}',
+                style: Theme.of(context).textTheme.bodyMedium,
+              ),
+            ],
+          ),
+        ),
+        Text(
+          switch (status) {
+            WordStatus.newWord => '新学',
+            WordStatus.recognized => '认识',
+            WordStatus.familiar => '熟悉',
+          },
+          style: Theme.of(context).textTheme.bodySmall,
+        ),
+        IconButton(
+          icon: const Icon(Icons.volume_up_outlined, size: 20),
+          onPressed: () => VoiceService.instance.speak(wordEnglish(id)),
+        ),
+      ],
+    );
+  }
+}