feat(gamification): hide locked achievements of disabled modules

When a teacher / admin turns off a module (per-class, per-role, or
globally), the matching achievements no longer clutter the user's
'Достижения' tab — but only the ones the user hasn't earned yet.
Already-unlocked achievements stay visible forever. We never take a
reward away after the fact.

Backend:
  • migration 034 adds achievements.required_feature + backfills 42
    rows (9 exam9, 8 red_book, 6 lab, 5 classroom, 4 textbooks, 3 each
    of biochem/flashcards, 2 live_quiz, 2 pet). 32 core rows stay
    NULL = always visible.
  • middleware/features.js gains computeFeaturesForUser(userId, role)
    + isFeatureEnabledForUser — extracted from server.js#/api/features
    so multiple consumers (gam achievements, future shop filter, etc.)
    apply the same global+class+free_student merge.
  • service.seedAchievements derives required_feature from track/group
    when ACHIEVEMENT_DEFS doesn't spell one out, and UPDATE-syncs it on
    every boot — keeps catalogue consistent across upgrades.
  • _shared.getAllAchs SELECT now returns required_feature.
  • gamification/api.getAchievements filters: drop locked rows whose
    required_feature is === false for this user. Missing flag = ON
    (opt-in disable model).

Verified: with exam9 + pet disabled, 12 locked achievements vanish from
the response while unlocked ones in those tracks remain.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/src/controllers/gamification/_shared.js

@@ -222,7 +222,7 @@ const stmts = {
   setUserGoalTier:   db.prepare('UPDATE users SET goal_tier = ? WHERE id = ?'),
   getAllAchs:        db.prepare(`
     SELECT id, slug, title, icon, category, description,
-           group_slug, track, tier, sort_order
+           group_slug, track, tier, sort_order, required_feature
       FROM achievements
      ORDER BY sort_order, id
   `),

backend/src/controllers/gamification/api.js

@@ -1,6 +1,7 @@
 'use strict';
 const db = require('../../db/db');
 const { stmts, GOAL_TIERS, AVATAR_FRAMES, rankName } = require('./_shared');
+const { computeFeaturesForUser } = require('../../middleware/features');
 const { getXPInfo, getDailyGoal, ensureChallenges, awardXP, awardCoins } = require('./service');
 
 /* ═══════════════════════════════════════════════════════════════════════
@@ -57,17 +58,33 @@ function setGoalTier(req, res) {
    Response stays an array (backward compatible). Each item now carries
    `group_slug` / `track` / `tier` / `sort_order` so the UI can group +
    order without an extra endpoint. Group display titles are hard-coded
-   client-side (small + stable). */
+   client-side (small + stable).
+
+   Feature gating: achievements whose `required_feature` is disabled for
+   this user (per merged global/class/free_student flags) are hidden —
+   but only if the user hasn't unlocked them yet. Already-earned
+   achievements are never taken away, even after the module is turned
+   off. */
 function getAchievements(req, res) {
   const all = stmts.getAllAchs.all();
   const unlocked = stmts.getUserAchs.all(req.user.id);
   const unlockedMap = {};
   for (const u of unlocked) unlockedMap[u.achievement_id] = u.unlocked_at;
-  const result = all.map(a => ({
-    ...a,
-    unlocked: !!unlockedMap[a.id],
-    unlocked_at: unlockedMap[a.id] || null,
-  }));
+
+  const feats = computeFeaturesForUser(req.user.id, req.user.role);
+
+  const result = [];
+  for (const a of all) {
+    const isUnlocked = !!unlockedMap[a.id];
+    // Hide locked achievements whose required_feature is explicitly off.
+    // Missing flag is treated as ON (opt-in disable model).
+    if (!isUnlocked && a.required_feature && feats[a.required_feature] === false) continue;
+    result.push({
+      ...a,
+      unlocked: isUnlocked,
+      unlocked_at: unlockedMap[a.id] || null,
+    });
+  }
   res.json(result);
 }
 

backend/src/controllers/gamification/service.js

@@ -117,12 +117,30 @@ function updateStreak(userId) {
 }
 
 /* ── Achievements ──────────────────────────────────────────────────── */
+/* Derive the required_feature flag for an achievement when its def
+   doesn't spell one out explicitly. Centralizes the mapping (track +
+   group → feature name) so future inserts in ACHIEVEMENT_DEFS inherit
+   the gating automatically — mirrors migration 034's backfill. */
+function _requiredFeatureFor(a) {
+  if (a.required_feature !== undefined) return a.required_feature;   // explicit wins
+  if (a.group === 'exam') return 'exam9';
+  if (a.track === 'red_book' || a.track === 'red_book_quest' || a.track === 'red_book_obs') return 'red_book';
+  if (a.track === 'biochem') return 'biochem';
+  if (a.track === 'lab' || a.track === 'lab_reactions') return 'lab';
+  if (a.track === 'classroom' || a.track === 'teacher') return 'classroom';
+  if (a.track === 'live_quiz') return 'live_quiz';
+  if (a.track === 'flashcards') return 'flashcards';
+  if (a.track === 'pet') return 'pet';
+  if (a.track === 'tb_progress') return 'textbooks';
+  return null;
+}
+
 function seedAchievements() {
   // INSERT for missing rows — supplies legacy + new taxonomy fields.
   const ins = db.prepare(`
     INSERT OR IGNORE INTO achievements
-      (slug, title, icon, category, description, group_slug, track, tier, sort_order)
-    VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?)
+      (slug, title, icon, category, description, group_slug, track, tier, sort_order, required_feature)
+    VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
   `);
   // UPDATE for existing rows — keep title/icon/desc/category fresh AND
   // backfill the taxonomy columns added by migration 030 (so installs
@@ -136,14 +154,16 @@ function seedAchievements() {
       group_slug = COALESCE(?, group_slug),
       track      = COALESCE(?, track),
       tier       = COALESCE(?, tier),
-      sort_order = ?
+      sort_order = ?,
+      required_feature = COALESCE(?, required_feature)
     WHERE slug = ?
   `);
   for (const a of ACHIEVEMENT_DEFS) {
+    const reqFeat = _requiredFeatureFor(a);
     ins.run(a.slug, a.title, a.icon, a.cat, a.desc,
-            a.group ?? null, a.track ?? null, a.tier ?? null, a.sort_order ?? 0);
+            a.group ?? null, a.track ?? null, a.tier ?? null, a.sort_order ?? 0, reqFeat);
     upd.run(a.icon, a.cat, a.title, a.desc,
-            a.group ?? null, a.track ?? null, a.tier ?? null, a.sort_order ?? 0,
+            a.group ?? null, a.track ?? null, a.tier ?? null, a.sort_order ?? 0, reqFeat,
             a.slug);
   }
 }