Dependency Injection

Constructor injection via Microsoft.Extensions.DependencyInjection. Dependencies MUST use interface types, not concrete types.

• Transient for lightweight stateless services
• Scoped for per-request services
• Singleton for thread-safe shared state
• A scoped service MUST NOT be injected into a singleton (captive dependency)
• Use IOptions<T> / IOptionsSnapshot<T> for configuration binding
• Keep registrations in Add*() extension methods for modularity

public static IServiceCollection AddMyFeature(this IServiceCollection services)
{
    services.AddSingleton<IFeatureManager, LocalFeatureManager>();
    services.AddTransient<IOrderService, OrderService>();
    return services;
}

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