requirements management

SKILL.md

The third type parameter in Effect represents requirements - services and dependencies the effect needs to run:

Effect uses a powerful dependency injection system based on Context and Layer.

The primary reason to define services is testability. Every external dependency (API calls, databases, file systems, third-party SDKs) MUST be wrapped in a Context.Tag service so that tests can provide a test implementation instead of hitting real systems. This is how Effect achieves 100% test coverage — business logic depends only on service interfaces, and tests swap in test layers that control all I/O.

在用户询问"Effect 服务"、"依赖注入"、"Effect.Tag"、"Context.Tag"、"Layer"、"Effect.provide"、"Effect.provideService"、"服务实现"、"管理依赖"、"Layer.succeed"、"Layer.effect"、"Layer.scoped"、"组合层"、"Layer.merge"、"Layer.provide"、"默认服务"、"层记忆化"、"可测试性"、"测试层"、"mock 服务"，或需要理解 Effect 如何处理 Requirements (R) 类型参数时使用。 来源：andrueandersoncs/claude-skill-effect-ts。

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