tutor answers step by step in plain text, islands finish, and the audit's money and login holes are closed

Tutor (prompt tutor-v3-stepwise-plain): plain text instead of LaTeX/markdown,
with rag/services/mathtext.py converting whatever still slips through; full
step-by-step solutions with a check before the final answer; three tones by
grade; the last 6 messages of the conversation go to the model and follow-ups
are no longer served from another user's cache; book solutions the checker
disputes are kept out of the context; a questionId gives the tutor the
practice question and the student's wrong answer. /api/health reports when
the AI credit runs out. rag_model_benchmark compares chat models on verified
book problems (run on the server; credit ran out mid-run).

Map: only lessons that have questions count toward finishing an island,
lessonIds[0] / nextLessonId is always the next lesson to play, and a finished
island stays finished. The Seyar characters (sigma/delta/pi) are seeded.

Audit fixes, each reproduced before fixing:
- the plan is stored on the order, so paying a monthly order after starting
  a yearly checkout no longer grants a year
- opening checkout no longer demotes an active subscription; renewals extend
  from the current expiry; expired subscriptions are not reported active
- one discount code per order and only before the gateway; a 100% code
  completes the purchase; lost Zarinpal confirmations are re-verified
- the unused /api/payment/webhook "mark paid" endpoint is removed
- XP counts only answers recorded on the server
- 6-digit OTP, each code dies after 5 wrong guesses; POST /api/auth/logout
- a guest who signs up keeps their account and progress (test phones excluded)
- affiliate commission on the first real payment; guests excluded
- parents with several children no longer get a 500
- SQLite runs transactions IMMEDIATE, since it ignores select_for_update
- admin login is rate-limited; display names drop phone numbers and links;
  userQuestion is capped at 2000 characters
- server-side heart enforcement exists behind HEARTS_ENFORCED (off until the
  frontend handles 403 no_hearts)

Not done on purpose: rotating the server's secret key and moving to Postgres.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

rag/services/retrieval.py

@@ -107,15 +107,23 @@ def _payload_text(payload: dict) -> str:
     دو شکلِ payload در دادهٔ تیمِ دیگه هست:
     - درس‌های متنی (علوم/اجتماعی): کلیدِ `summary`
     - ریاضی: کلیدِ `generalSolution` (+ problem/solution) و بدونِ `summary`
+
+    ⚠️ راه‌حلی که `rag_verify_solutions` با آن مخالفت کرده (`disagrees`) به مدل
+    نمی‌رسد؛ فقط روش و صورتِ مسئله می‌رود. پیش‌تر همان راه‌حلِ غلط (مثلاً «در
+    [−π, π] دو نوسانِ کامل») به‌عنوانِ «متنِ درس» به دستیار داده می‌شد و دستیار
+    تکرارش می‌کرد — حدودِ ۱۳٪ تکه‌های کتاب‌های دهم تا دوازدهم این‌طورند.
     """
     if payload.get('summary'):
         return payload['summary']
+    solution = payload.get('solution', '')
+    if payload.get('solution_verdict') == 'disagrees':
+        solution = ''
     parts = [
-        payload.get('generalSolution', ''),
-        payload.get('problem', ''),
-        payload.get('solution', ''),
+        ('روش', payload.get('generalSolution', '')),
+        ('مسئله', payload.get('problem', '')),
+        ('راه‌حلِ کتاب', solution),
     ]
-    joined = '\n'.join(p for p in parts if p).strip()
+    joined = '\n'.join(f'{label}: {text}' for label, text in parts if text).strip()
     return joined or payload.get('text', '')