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>

discount/views.py

@@ -146,6 +146,17 @@ class RedeemDiscountView(APIView):
                 if order_locked.status != 'pending':
                     raise ValidationError({'code': 'این سفارش دیگر قابل اعمال تخفیف نیست.'})
 
+                # بعد از رفتن به درگاه، authorityِ زرین‌پال با مبلغِ قبلی گرفته شده و
+                # دوباره استفاده می‌شود؛ تخفیف در این لحظه یعنی کاربر مبلغِ قبلی را
+                # می‌پردازد ولی verify با مبلغِ جدید رد می‌شود — پول کم می‌شود و
+                # اشتراکی فعال نمی‌شود.
+                if order_locked.gateway_authority:
+                    raise ValidationError({'code': 'کدِ تخفیف را پیش از رفتن به درگاهِ پرداخت وارد کنید.'})
+
+                # یک کد برای هر سفارش: کدهای درصدی روی هم جمع می‌شدند.
+                if Redemption.objects.filter(order_id=order_locked.id).exists():
+                    raise ValidationError({'code': 'روی این سفارش قبلاً کدِ تخفیف اعمال شده است.'})
+
                 if discount.type == 'percent':
                     discount_amount = order_locked.amount * discount.value // 100
                 else:
@@ -160,11 +171,23 @@ class RedeemDiscountView(APIView):
                 # مبلغ سفارش واقعاً کم می‌شود تا مرحله‌ی پرداخت مبلغ تخفیف‌خورده را ببیند.
                 order_locked.amount = max(order_locked.amount - discount_amount, 0)
                 order_locked.save(update_fields=['amount'])
+
+                # سفارشِ صفرتومانی را هیچ درگاهی نمی‌پذیرد؛ کدِ ۱۰۰٪ یعنی خرید
+                # همین‌جا تمام است (همان مسیرِ پرداختِ واقعی: اشتراک، اعلان، پورسانت).
+                if order_locked.amount == 0:
+                    from payment.services import apply_order_payment_result
+                    apply_order_payment_result(
+                        order=order_locked, gateway='discount',
+                        gateway_ref_id=f'discount-{discount.id}-order-{order_locked.id}',
+                        new_status='paid', event='discount_full',
+                    )
         except IntegrityError:
             # fallback برای رقابت هم‌زمان روی قید یکتایی، حتی اگر قفل select_for_update رد شود.
             raise ValidationError({'code': 'این کد دیگر معتبر نیست یا سقف استفاده‌اش پر شده.'})
 
-        data = {'success': True, 'discountAmount': discount_amount}
+        order.refresh_from_db(fields=['status', 'amount'])
+        data = {'success': True, 'discountAmount': discount_amount,
+                'orderStatus': order.status, 'amount': order.amount}
         return Response(RedeemResponseSerializer(data).data)