> Ideally all programs should be isolated from the underlying filesystem and be able to read only their own files and files from per-program data directory
So how will you spam all the group chats you're on with meme gifs downloaded from facebook then? :)
Download an image from Facebook into browser's private downloads directory, copy it using a file-manager application (one of the exceptional applications having full filesystem access) into Telegram's private directory, upload it into chats you need to post it.
The file-manger application managed above is a single point of failure, of course. So, it should be allowed to use only one provided by OS vendor.