Putting it together

Load the steps from a folder, then run them. bindAsync runs the pipeline only if the steps loaded, and mapLeft turns the load errors into the pipeline’s error type, so the whole flow is one EitherAsync:

import { left, right } from "@ngwes/mini-fp";
import { Pipeline, loadStepsFromDir } from "@ngwes/groucho-fp";
import type { LoadError, PipelineOptions } from "@ngwes/groucho-fp";

type Ctx = { userId: string; profile?: Record<string, unknown>; welcomed?: boolean };
type Err =
  | { tag: "load-failed"; errors: ReadonlyArray<LoadError> }
  | { tag: "not-found"; userId: string }
  | { tag: "crash"; cause: unknown }
  | { tag: "conflict"; keys: ReadonlyArray<string> };

const options: PipelineOptions<Err, Ctx> = {
  onLeft: (error, ctx) => {
    console.warn(`user ${ctx.userId}: ${error.tag}`);
    return left(error);
  },
  onException: (exception) => left({ tag: "crash", cause: exception }),
  onConflictingKeys: (keys, ctx, next) =>
    keys.length === 1 && keys[0] === "profile" ? right(next) : left({ tag: "conflict", keys }),
};

const outcome = await loadStepsFromDir<Err, Ctx>("./steps")
  .mapLeft((errors): Err => ({ tag: "load-failed", errors }))
  .bindAsync((steps) => Pipeline({ userId: "42" }, steps, options))
  .match(
    (ctx) => `done: ${JSON.stringify(ctx)}`,
    (error) => `failed: ${error.tag}`,
  );

console.log(outcome);