class UserService extends Effect.Service<UserService>()("UserService", {
  dependencies: [DatabaseService.Default],
  effect: Effect.gen(function* () {
    const db = yield* DatabaseService

    return {
      findById: Effect.fn("UserService.findById")(
        (id: UserId) => db.query(/* ... */)
      ),
    }
  }),
}) {}

// Usage - dependencies auto-provided
UserService.findById(userId)

// Define domain-specific errors
class UserNotFoundError extends Schema.TaggedError<UserNotFoundError>()(
  "UserNotFoundError",
  { userId: UserId, message: Schema.String }
) {}

// Handle with catchTag (preserves type info)
effect.pipe(
  Effect.catchTag("UserNotFoundError", (e) => /* handle */),
  Effect.catchTag("AuthExpiredError", (e) => /* handle */)
)

// Branded ID
const UserId = Schema.String.pipe(Schema.brand("@App/UserId"))

// Domain entity with Schema.Class
class User extends Schema.Class<User>("User")({
  id: UserId,
  email: Schema.String,
  createdAt: Schema.DateFromSelf,
}) {
  get displayName() { return this.email.split("@")[0] }
}

// Declare dependencies in service, not at usage
const MainLayer = Layer.mergeAll(
  UserServiceLive,
  AuthServiceLive,
  DatabaseLive
)

// Run program
Effect.runPromise(program.pipe(Effect.provide(MainLayer)))