You will not notice a cost regression by reading an invoice. Invoices arrive after the traffic, after the incident review, and after the person who wrote the expensive loop has moved to another team. You need the build to tell you, on the commit that caused it, with a number and a threshold and someone's name on it. That means treating cost per successful outcome as a test assertion. Same as a snapshot test, same as a schema check: a fixture, a threshold, a deterministic runner, and a red bui...