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/clients.py

@@ -50,6 +50,24 @@ def get_qdrant_client():
     )
 
 
+def is_account_limit(exc) -> bool:
+    """
+    آیا این خطا یعنی «حسابِ سرویس دیگر جواب نمی‌دهد» یا فقط کندیِ لحظه‌ای؟
+
+    دو شکلِ واقعی که دیدیم و هر دو باید اجرا را متوقف کنند:
+        429  initial_usage_limit_exceeded  — سقفِ حسابِ تازه، ساعت‌ها
+        403  insufficient user quota       — اعتبار تمام شده
+
+    نکته: متنِ دومی «insufficient user quota» است با فاصله، نه زیرخط. محافظِ
+    اولِ ما دنبالِ `insufficient_quota` می‌گشت و نمی‌گرفتش، و اجرا ۷۷۰ فراخوانیِ
+    محکوم‌به‌شکست زد به‌جای اینکه سرِ اولی بایستد.
+    """
+    text = str(exc).lower()
+    if 'usage_limit' in text or 'quota' in text:
+        return True
+    return '403' in text and 'insufficient' in text
+
+
 def reset_clients_cache():
     """برای تست‌ها / بعد از تغییرِ settings در زمانِ اجرا."""
     get_openai_client.cache_clear()