@ai-sdk/rsc/src/util/is-async-generator.ts

[React Server Components](https://react.dev/reference/rsc/server-components) for the [AI SDK](https://ai-sdk.dev/docs):

export function isAsyncGenerator<T, TReturn, TNext>(
  value: unknown,
): value is AsyncGenerator<T, TReturn, TNext> {
  return (
    value != null && typeof value === 'object' && Symbol.asyncIterator in value
  );
}