Function parseEnum

packages/cli/src/commands/lambda.ts:446–456

* Parse a string-union flag against a closed set of allowed values. * Returns `defaultValue` (which may be `undefined`) when the input is * empty; throws with a flag-specific message when the value is set * but unrecognised.

(
  raw: unknown,
  allowed: readonly T[],
  errorPrefix: string,
  defaultValue: T | undefined,
)

 * but unrecognised.
 */
function parseEnum<T extends string>(
  raw: unknown,
  allowed: readonly T[],
  errorPrefix: string,
  defaultValue: T | undefined,
): T | undefined {
  if (raw === undefined || raw === null || raw === "") return defaultValue;
  const s = String(raw);
  if ((allowed as readonly string[]).includes(s)) return s as T;
  throw new Error(`${errorPrefix} must be ${allowed.join("|")}; got ${s}`);
}

const FORMATS = [
  "mp4",