This sounds like the panicky adverts from 20-odd years ago "YOUR COMPUTER IS LEAKING YOUR IP ADDRESS!!11!!""2!!2!!"

Link previews even! Just paste it into a group chat and everyone’s message clients will happily issue a GET request.

That's not how it works. The chat app requests the link preview and caches it.

That’s how link previews work on iOS (it was the cause of the zero click RCE a few years ago by executing row hammer through WebView), so I guess it depends on your software.

It's a possibility, but it's not how these kernel panic viewer websites are currently implemented. They do the decoding on the clientside, with the data stored in the URL fragment, which is not sent to the server by default.

Still good to have alternative implementations, though. The Javascript could be silently stealing the URL fragment on only specific requests, so there's no real way to audit it to be sure.

This is why I like to use Binary Eye, it never acts on anything automatically when scanning a code, you have to tell it to.