`files.download` doesn't properly wait until the operation finishes

[wangcheng]

files.download doesn't properly wait until the operation finished. So it is impossible to read the file immediately after downloading it.

After reading the code. I believe it is a bug with the NodeDownloader.download method.

https://github.com/googleapis/js-genai/blob/main/src/node/_node_downloader.ts#L30

There is a PR trying to fix this but it didn't fix all the branches in download function. We also need to properly wait for the pipeline to finish. I drafted a PR to fix this branch.

Environment details

• Programming language: TypeScript
• OS: MacOS
• Language runtime version: Node.js 22
• Package version: 1.10.0

Steps to reproduce

1. use files.download download to download a file
2. read the file immediately using an async API.
3. notice the file size doesn't reflect the actual file size.

// we are using await here but it doesn't wait until the file is finished being written.
await gemini.files.download({
  file: video, // for example a generated video
  "/tmp/video.mp4",
});

fs.stat(downloadPath, (err, file) => {
  console.log(file.size); // the size is not complete
});