Business rule: the 35 EGP development fee is a flat non-discountable surcharge
added AFTER all discounts are applied. Discount applies only to base_amount.

Correct formula: discount = base × pct, total = (base - discount) + dev_fee
Previous (wrong): discount = (base + dev_fee) × pct

For member 51 (2023/2024): 410×50% = 205 discount, total = 205 + 35 = 240
(was incorrectly: 445×50% = 222.50, total = 222.50)
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>