Lesson 2: OCP with Strategy

This lesson practices OCP with Strategy at real C# application level. We start from design pain, study code, practice a small decision, predict behavior, and verify mastery.

Add a new discount by adding a class, not editing the checkout engine.

OCP with Strategy: Add a new discount by adding a class, not editing the checkout engine.
design pressure: A repeated change, duplication, or test pain that signals the model needs a better boundary.