microsoft-extensions-dependency-injection

What problem does it solve? ASP.NET Core applications often accumulate hundreds of unorganized service registrations in Program.cs, making configuration hard to navigate, reuse in tests, and maintain across teams. This Skill provides patterns for structuring dependency injection registrations into cohesive, testable extension methods. ## Core Features & Use Cases - Extension Method Composition: Group related registrations into Add{Feature}Services() methods placed next to the services they register, keeping Program.cs clean and chainable. - Lifetime Management Guidance: Choose correctly between Singleton, Scoped, and Transient lifetimes, and avoid common mistakes like injecting scoped services into singletons. - Scope Handling in Background Work: Create manual scopes in BackgroundService and Akka.NET actors where no automatic request scope exists. - Use Case: When building an order-processing API, register AddOrderServices(), AddEmailServices(), and AddPaymentServices() in Program.cs, then reuse those same extensions in WebApplicationFactory tests while overriding only external dependencies like payment processors. ## Quick Start Refactor my Program.cs service registrations into feature-based IServiceCollection extension methods with correct lifetimes.