As described here https://github.com/WICG/shared-storage#writing-to-shared-storage-via-response-headers
I'm trying to set shared storage using via response headers.

var x = new XMLHttpRequest();
x.setRequestHeader("sharedStorageWritable", "true");
and so on...

The origin send Sharedstoragewritable in the request header with value true
The response header contains the Shared-Storage-Write but nothing is written into origin shared storage.

I do not see the Sec-Shared-Storage-Writable in the request header as I would expected.

I did a test also on same domain to avoid any permissions checks issues.