Change-based regression

Change-based regression starts from the diff. For each release it asks what changed in code, configuration, data and third-party services, and which user journeys those changes can reach. Those journeys are re-tested; the rest rely on the standing core checks.

It works when the map from change to journey is honest. A small diff can still break checkout if it touches a shared payment adapter, and a configuration change with no code at all can break sign-in. I read the release diff with a developer, and I compare configuration between releases myself.

The method does not replace a fixed core of critical journeys. It decides where the remaining time goes.