Describe the bug

This is a duplicate of #12157. I am opening this bug due to it is closed and can't proceed with it.
As the title: SSE close event is not being forwarded to the server when using Vite as Reverse Proxy.
In the dev server and in the preview server, both are not forwarding the close event to the server.
After many hours of debugging, and traffic inspection, after calling sse.close(), the connection is closed between the client and the proxy, but still open between the proxy and the server!

Reproduction

#12157

Steps to reproduce

No response

System Info

Ubuntu.

Used Package Manager

pnpm

Logs

No response

Validations

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