ComfyUI WAN performance degrades over time, link eventually saturates

### 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

Remote WAN access remains stable across a sustained session. Image delivery speed is limited only by available bandwidth. A batch of 4 images (~4 MB each) should deliver in a comparable timeframe to LAN, where the same batch renders in the browser within 1–2 seconds of processing completing.

### Actual Behavior

Performance degrades steadily with each generation cycle over WAN. Initially images load within a reasonable time, but throughput gradually collapses to 20–50 KB/s. Images sit on `pending` in DevTools Network view for 20 seconds to 2 minutes. In a batch of 4, only 1 or 2 may ever render. After sustained use the host machine's network saturates entirely — SSH and RDP access to the machine are lost. Restarting ComfyUI resolves it temporarily, but the degradation always returns.

### Steps to Reproduce

1. Start ComfyUI with `python main.py --listen 0.0.0.0`
2. Access the UI from a WAN connection
3. Generate several batches of images over a sustained session
4. Observe throughput collapsing and images hanging on `pending` in DevTools
5. Continue generating — eventually all remote connectivity to the host is lost

### Debug Logs

```powershell
No specific error output from ComfyUI. The degradation is observable in the browser DevTools Network tab (requests stuck on `pending`, reported throughput 20–50 KB/s) and via loss of SSH/RDP sessions to the host machine.
```

### Other

- Tested on: Windows, `python main.py --listen 0.0.0.0`
- GPU: RTX 5090 / 32 GB VRAM
- Running Windows Portable edition on a Windows 10 x64 computer

The issue does not reproduce on LAN. It reproduces identically across three independent WAN connections (work network, hotel Wi-Fi, 5G), ruling out any single network as the cause. FTP transfers to the same machine without ComfyUI running are fast in both directions on all three connections, ruling out bandwidth as a factor.

Start with the `python main.py --listen 0.0.0.0` entry point and reproduce the issue over WAN while watching the browser DevTools Network tab. Compare sustained batches over WAN and LAN, including requests stuck on `pending` and host connectivity through SSH/RDP. Done means image delivery remains stable and the host network does not saturate during prolonged generation.

Written by the indexing model from the issue text.