The loyalty team wants to celebrate customers whenever they place a new personal-best paid order.
A personal best is an order with status = 'paid' whose amount_usd is strictly greater than every earlier paid order amount from that same customer.
The first paid order for a customer counts as a personal best, because the customer has no earlier paid orders. An order that ties an earlier best does not count. Non-paid orders, including refunded and cancelled orders, must not appear and must not affect the customer's previous-best amount.
Guest orders have no customer history and should not appear in this report.
Ordering: Sort by customer_id, then order_ts, both in ascending order.