Stairway to Reliable Database Deployments Level 2 - Defining the Deployment Contract

Level 2 formalizes the behavioral guarantees that a changeset must provide in order to be safely deployed and rolled back. It introduces the deployment contract, checkpoint semantics, and the structural scope of Create and Rollback scripts. Data changes are addressed through a dedicated Update mechanism, with clear boundaries and limitations. By the end of this level, a changeset becomes a predictable and well-defined unit that can be reasoned about independently of execution context.