Effect v4 implementation and migration guidance for current Effect APIs. Use when writing or reviewing code that depends on Effect v4, migrating v3-style APIs (Context.Tag, Effect.Service, FiberRef, catchAll/catchSome, fork/forkDaemon), debugging service/layer wiring, or validating compatibility with effect-smol/effect@4.0.0-beta.x.
This skill includes a SKILL.md with agent instructions.