v0.32 embedded downloader failing

### Custom Node Testing

- [x] I have tried disabling custom nodes and the issue persists (see [how to disable custom nodes](https://docs.comfy.org/troubleshooting/custom-node-issues#step-1%3A-test-with-all-custom-nodes-disabled) if you need help)

### Expected Behavior

When adding new workflow template, attempting to resolve missing node/model errors, clicking Download should download the listed files.

### Actual Behavior

Clicking Download or Download All has no effect.

### Steps to Reproduce

Open a workflow that yields missing resource errors and try to download the listed files.

### Debug Logs

```powershell
Log is no a different computer. Last 4 entries in console log are:

[Save Media] Error: HTTP Error 404: Not Found
```

### Other

Required files can be downloaded via web browser at same links.

Start by reproducing the issue with a workflow template that reports missing resources, then inspect the Download and Download All flow and its console output. Use the reported HTTP 404 and compare the embedded downloader with downloading the same links in a browser; done means the listed files download successfully and the missing-resource errors are resolved.

Written by the indexing model from the issue text.