fix(exam-prep): практика/тренажёр берут только выверенные варианты (дедуп)

Тренажёр-по-темам и практика брали FROM exam_tasks без фильтра по варианту — в пул
попадали год-пачки (variant=год≥2011) и variant=0, которые ДУБЛИРУЮТ выверенные
варианты-пробники (51 дубль чистый↔пачка, 20 через variant=0). Ученик мог получить
одну задачу дважды.

Добавлен фильтр variant BETWEEN MV_LO..MV_HI (тот же [101;1999], что у пикера) во все
7 запросов выборки/счёта задач: practiceRandom, practiceUnsolved, topicTasksUnsolved,
topicTasksAny, listTopicsWithCounts (счётчик подтем), weakBatchTasks, pickRandomByDifficulty
(×2). Хелперы MV_LO/MV_HI (для math9 без диапазона — всё, кроме variant=0).

Результат: практика ctmath = только варианты 101–117 (496 задач, 0 дублей между собой),
год-пачки (714 задач) остаются в БД для возможного будущего, но не показываются.
Обратимо, без удаления данных. Рантайм-проверка: 5 эндпоинтов практики/тем → 200.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/src/routes/exam-prep.js

@@ -29,6 +29,11 @@ const isMockVariant = (examKey, v) => {
   const r = MOCK_VARIANT_RANGE[examKey];
   return r ? (v >= r[0] && v <= r[1]) : (v >= 1);
 };
+// Границы вариантов для практики/тренажёра: тот же фильтр, что у пикера, чтобы
+// год-пачки (variant=год≥2011) и variant=0 НЕ попадали в выборку задач и не
+// дублировали выверенные варианты-пробники. Для треков без диапазона — всё, кроме 0.
+const MV_LO = ek => (MOCK_VARIANT_RANGE[ek] ? MOCK_VARIANT_RANGE[ek][0] : 1);
+const MV_HI = ek => (MOCK_VARIANT_RANGE[ek] ? MOCK_VARIANT_RANGE[ek][1] : 1e15);
 
 /* Человекочитаемая подпись варианта (номер в БД остаётся техническим, напр. 101).
    Для ctmath варианты-пробники именуются по источнику; при добавлении новых
@@ -131,6 +136,7 @@ const SQL = {
       answer, solution_html, topic, subtopic, difficulty, textbook_slug, textbook_paragraph
       FROM exam_tasks
      WHERE exam_key = ?
+       AND variant BETWEEN ? AND ?
        AND task_type IN ('mc','open')
      ORDER BY RANDOM()
      LIMIT ?
@@ -161,6 +167,7 @@ const SQL = {
       t.textbook_slug, t.textbook_paragraph
       FROM exam_tasks t
      WHERE t.exam_key = ?
+       AND t.variant BETWEEN ? AND ?
        AND t.task_type IN ('mc','open')
        AND NOT EXISTS (
          SELECT 1 FROM exam_attempts a
@@ -350,7 +357,7 @@ const SQL = {
           FROM exam_tasks t
           LEFT JOIN exam_attempts a
             ON a.exam_task_id = t.id AND a.user_id = ?
-         WHERE t.exam_key = ? AND t.subtopic IS NOT NULL
+         WHERE t.exam_key = ? AND t.variant BETWEEN ? AND ? AND t.subtopic IS NOT NULL
          GROUP BY t.subtopic
       ) stat ON stat.subtopic = tp.slug
      WHERE tp.exam_key = ?
@@ -364,7 +371,7 @@ const SQL = {
     SELECT id, task_idx, variant, task_type, text_html, figure_html, opts_json,
            answer, solution_html, topic, subtopic, difficulty, textbook_slug, textbook_paragraph
       FROM exam_tasks t
-     WHERE t.exam_key = ? AND t.subtopic = ?
+     WHERE t.exam_key = ? AND t.variant BETWEEN ? AND ? AND t.subtopic = ?
        AND t.task_type IN ('mc','open')
        AND NOT EXISTS (
          SELECT 1 FROM exam_attempts a
@@ -378,7 +385,7 @@ const SQL = {
     SELECT id, task_idx, variant, task_type, text_html, figure_html, opts_json,
            answer, solution_html, topic, subtopic, difficulty, textbook_slug, textbook_paragraph
       FROM exam_tasks t
-     WHERE t.exam_key = ? AND t.subtopic = ?
+     WHERE t.exam_key = ? AND t.variant BETWEEN ? AND ? AND t.subtopic = ?
        AND t.task_type IN ('mc','open')
      ORDER BY RANDOM()
      LIMIT ?
@@ -437,6 +444,7 @@ const SQL = {
              answer, solution_html, topic, subtopic, difficulty, textbook_slug, textbook_paragraph
         FROM exam_tasks t
        WHERE t.exam_key = ?
+         AND t.variant BETWEEN ? AND ?
          AND t.subtopic IN (${ph})
          AND t.task_type IN ('mc','open')
          AND NOT EXISTS (
@@ -445,7 +453,7 @@ const SQL = {
          )
        ORDER BY RANDOM()
        LIMIT ?
-    `).all(examKey, ...slugs, userId, count);
+    `).all(examKey, MV_LO(examKey), MV_HI(examKey), ...slugs, userId, count);
   },
 };
 
@@ -693,6 +701,7 @@ function pickRandomByDifficulty(examKey, count, excludeSlugs) {
   const exClause = exParams
     ? `AND (subtopic IS NULL OR subtopic NOT IN (${exParams.map(() => '?').join(',')}))`
     : '';
+  const mvLo = MV_LO(examKey), mvHi = MV_HI(examKey);
 
   const COLS = `id, task_idx, variant, task_type, text_html, figure_html, opts_json,
              answer, solution_html, topic, subtopic, difficulty, textbook_slug, textbook_paragraph`;
@@ -704,14 +713,14 @@ function pickRandomByDifficulty(examKey, count, excludeSlugs) {
     const sql = `
       SELECT ${COLS}
         FROM exam_tasks
-       WHERE exam_key = ? AND task_type IN ('mc','open')
+       WHERE exam_key = ? AND variant BETWEEN ? AND ? AND task_type IN ('mc','open')
          AND difficulty = ?
          ${exClause}
        ORDER BY RANDOM()
        LIMIT ?`;
     const args = exParams
-      ? [examKey, d, ...exParams, limit]
+      ? [examKey, mvLo, mvHi, d, ...exParams, limit]
-      : [examKey, d, limit];
+      : [examKey, mvLo, mvHi, d, limit];
     for (const r of db.prepare(sql).all(...args)) { if (!seen.has(r.id)) { seen.add(r.id); out.push(r); } }
   }
   // Backfill to `count` from any difficulty — covers tracks whose tasks don't
@@ -722,12 +731,12 @@ function pickRandomByDifficulty(examKey, count, excludeSlugs) {
     const sql = `
       SELECT ${COLS}
         FROM exam_tasks
-       WHERE exam_key = ? AND task_type IN ('mc','open')
+       WHERE exam_key = ? AND variant BETWEEN ? AND ? AND task_type IN ('mc','open')
          ${exClause}
          ${notIn}
        ORDER BY RANDOM()
        LIMIT ?`;
-    const args = [examKey, ...(exParams || []), ...ids, count - out.length];
+    const args = [examKey, mvLo, mvHi, ...(exParams || []), ...ids, count - out.length];
     out.push(...db.prepare(sql).all(...args));
   }
   out.sort((a, b) => (a.difficulty || 0) - (b.difficulty || 0));
@@ -767,7 +776,7 @@ router.get('/:examKey/practice/next', (req, res) => {
     weakSlugs = SQL.weakTopicSlugs.all(req.user.id, examKey).map(r => r.slug);
     if (weakSlugs.length === 0) {
       // No weak topics yet → fall back to unsolved so the button still works
-      rows = SQL.practiceUnsolved.all(examKey, req.user.id, count);
+      rows = SQL.practiceUnsolved.all(examKey, MV_LO(examKey), MV_HI(examKey), req.user.id, count);
       strategy = 'unsolved-fallback';
     } else {
       rows = SQL.weakBatchTasks(examKey, weakSlugs, req.user.id, count);
@@ -777,8 +786,8 @@ router.get('/:examKey/practice/next', (req, res) => {
       }
     }
   } else if (strategy === 'unsolved') {
-    rows = SQL.practiceUnsolved.all(examKey, req.user.id, count);
+    rows = SQL.practiceUnsolved.all(examKey, MV_LO(examKey), MV_HI(examKey), req.user.id, count);
-    if (!rows.length) rows = SQL.practiceRandom.all(examKey, count);
+    if (!rows.length) rows = SQL.practiceRandom.all(examKey, MV_LO(examKey), MV_HI(examKey), count);
   } else {
     // Random: difficulty-ordered batch, position 1 = difficulty 1.
     rows = pickRandomByDifficulty(examKey, count, excludeSlugs);
@@ -786,7 +795,7 @@ router.get('/:examKey/practice/next', (req, res) => {
     if (!rows.length && excludeSlugs.length) {
       rows = pickRandomByDifficulty(examKey, count, []);
     }
-    if (!rows.length) rows = SQL.practiceRandom.all(examKey, count);
+    if (!rows.length) rows = SQL.practiceRandom.all(examKey, MV_LO(examKey), MV_HI(examKey), count);
   }
 
   const refMap = getTopicRefMap(examKey);
@@ -1014,7 +1023,7 @@ router.get('/:examKey/topics', (req, res) => {
   const { examKey } = req.params;
   if (!SQL.getTrack.get(examKey)) return res.status(404).json({ error: 'Unknown exam track' });
 
-  const rows = SQL.listTopicsWithCounts.all(req.user.id, examKey, examKey);
+  const rows = SQL.listTopicsWithCounts.all(req.user.id, examKey, MV_LO(examKey), MV_HI(examKey), examKey);
 
   // Build {sections: [{slug,title,subtopics:[...]}]}
   const byParent = new Map();
@@ -1071,10 +1080,10 @@ router.get('/:examKey/topics/:slug/tasks', (req, res) => {
 
   let rows;
   if (excludeSolved) {
-    rows = SQL.topicTasksUnsolved.all(examKey, slug, req.user.id, count);
+    rows = SQL.topicTasksUnsolved.all(examKey, MV_LO(examKey), MV_HI(examKey), slug, req.user.id, count);
-    if (!rows.length) rows = SQL.topicTasksAny.all(examKey, slug, count);
+    if (!rows.length) rows = SQL.topicTasksAny.all(examKey, MV_LO(examKey), MV_HI(examKey), slug, count);
   } else {
-    rows = SQL.topicTasksAny.all(examKey, slug, count);
+    rows = SQL.topicTasksAny.all(examKey, MV_LO(examKey), MV_HI(examKey), slug, count);
   }
 
   const refMap = getTopicRefMap(examKey);