relay: Skill for Claude Code

Effect Client Wrapper Pattern

Wrap third-party SDK clients with Effect using the "use" pattern for consistent error handling, tracing, and dependency injection.

Pattern Structure

import { Context, Data, Effect, Layer, Config, Redacted } from "effect";

// 1. Define tagged errors
export class MyClientError extends Data.TaggedError("MyClientError")<{
  cause: unknown;
}> {}

export class MyClientInstantiationError extends Data.TaggedError("MyClientInstantiationError")<{
  cause: unknown;
}> {}

// 2. Define service interface with `use` method
export type IMyClient = Readonly<{
  client: ThirdPartyClient;
  use: <A>(fn: (client: ThirdPartyClient) => Promise<A>) => Effect.Effect<A, MyClientError, never>;
}>;

// 3. Create the service implementation
const make = Effect.gen(function* () {
  const apiKey = yield* Config.redacted("MY_CLIENT_API_KEY");

  const client = yield* Effect.try({
    try: () => new ThirdPartyClient(Redacted.value(apiKey)),
    catch: (cause) => new MyClientInstantiationError({ cause }),
  });

  const use = <A>(fn: (client: ThirdPartyClient) => Promise<A>) =>
    Effect.tryPromise({
      try: () => fn(client),
      catch: (cause) => new MyClientError({ cause }),
    }).pipe(Effect.withSpan(`my_client.${fn.name ?? "use"}`));

  return { client, use };
});

// 4. Export as Context.Tag with Default layer
export class MyClient extends Context.Tag("MyClient")<MyClient, IMyClient>() {
  static Default = Layer.effect(this, make).pipe(Layer.annotateSpans({ module: "MyClient" }));
}

Usage

const program = Effect.gen(function* () {
  const myClient = yield* MyClient;

  const result = yield* myClient.use((client) => client.someMethod({ param: "value" }));

  return result;
});

// Run with layer
program.pipe(Effect.provide(MyClient.Default));

Key Benefits

1. Centralized error handling - All client errors wrapped in typed MyClientError
2. Automatic tracing - Every use call creates a span with function name
3. Config-based secrets - API keys loaded via Config.redacted
4. Clean DI - Consumers inject via yield* MyClient
5. Encapsulation - Raw client hidden behind use interface