Upgrading an API breaks your code in ways the types and the changelog don't show.

You bump a dependency, or a provider ships a new version. Your code still compiles and still passes review, then it fails in production, because a value the API returns now means something different. These are not the renamed fields or removed endpoints your types and your tests already catch. They are changes in behavior, and nothing flags them until they run.

Repertoire finds what an upgrade breaks in your code and migrates it. Then it runs the fix against both the old and the new version to prove it holds, so the bump and the migration land together, already checked.

Dependabot raises the version number and leaves the rest to you. It does not know a value changed meaning, so it cannot write the migration or check it. Repertoire finds the behavioral break, writes the migration, and gives you a test that fails before the fix and passes after.