Appending an Emittance and Retrieving Last Stream Value

/* pipe ...*/
Stream.flatMap(({ response, body, parsedLength }) =>
            ReadableStreamStream(body).pipe(
                Stream.map(({ length, stuff }) => ({
                    length,
                    stuff,
                    done: false,
                    progress: length / parsedLength,
                })),
                Stream.onDone(latestValues => /* do something with the latest chunk - this doesn't work because onDone doesn't take arguments */),
            ),
        ),
/* ... */