Function createLegacyFs

packages/just-bash/src/encoding.fs-fallback.test.ts:19–33

* Wrap an InMemoryFs in a Proxy that hides `readFileBytes`, forcing every * caller down the fallback path. Delegates everything else.

(seed: Record<string, string>)

 * caller down the fallback path. Delegates everything else.
 */
function createLegacyFs(seed: Record<string, string>): IFileSystem {
  const inner = new InMemoryFs(seed);
  return new Proxy(inner, {
    get(target, prop, receiver) {
      if (prop === "readFileBytes") return undefined;
      const value = Reflect.get(target, prop, receiver);
      // Methods need to keep their `this` bound to the inner instance.
      return typeof value === "function" ? value.bind(target) : value;
    },
    has(target, prop) {
      if (prop === "readFileBytes") return false;
      return Reflect.has(target, prop);
    },
  }) as IFileSystem;
}

describe("readFileBytes back-compat fallback", () => {
  it("commands work against a custom IFileSystem missing readFileBytes", async () => {