fix: harden gift subscription feature after multi-agent review
- Add self-gift prevention (telegram username + email)
- Unify 404 response on purchase status (eliminate token oracle)
- Add period_days upper bound (le=3650) in schema
- Handle NULL paid_at in retry query with or_()
- Capture purchase_token before fulfill_purchase (session safety)
- Upgrade Bot API pre-check logging to warning level
- Add exc_info=True for monitoring retry errors
- Add database indexes: (user_id, is_gift, status), (status, paid_at), buyer_user_id
- Use datetime instead of str for created_at in PendingGiftResponse
- Align GuestPurchase model __table_args__ with all migrations
Fringg
6a4140e3e2