New feature. Existing app. Everything could break.

It is Monday morning. The product manager confirms that the new Loyalty Points feature must go live this Friday. The feature has been built over the past three weeks by two developers. It adds a points calculation engine that hooks into the Order Service at checkout, deducts or credits points from the User Account Service, and logs every transaction to a new LoyaltyLedger table. The existing Order Service processes 12,000 transactions per day in production. No one has mapped exactly which existing code paths the new hooks touch. You are the senior engineer responsible for delivery.