Thanks, sindy! That’s a really good tip, and hopefully may be of help to others.
As it turns out, I saw that suggested elsewhere as a general workaround to the lack of a file-copy command.
Unfortunately, in my specific case it stalls.
Per my wacky theory, ftp to localhost/loopback (127.0.0.1) also fails since part/all of the networking stack is offline, and ultimately anything with IP addresses that is associated with an interface (via a default route in case of the loopback address?) seems to stall out the console.
It’s a long shot, but I guess I could see if the /tool fetch url command respects something like file:// urls…
→ I’m wondering if there might not be some rare issue with corruption in the v6.48.1 release (maybe plus/minus some unknown number of builds), maybe in combination with the drivers / kernel extensions for certain architectures and/or specific switch chipsets.
See this reply to “v6.48.1 [stable] is released!”. (There’s also the very next reply in the same thread, but that could have many causes.)