A weird thing about #Slack on #Linux#X11: whenever it gains keyboard focus, it immediately reads the X11 clipboard, even if you didn't try to paste anything. I see no evidence that it does anything with what it reads, but I know it reads it.
I found this out by accident, because I wrote a stunt X11 client which owns the clipboard for just long enough to paste once, and then terminates. The idea was to queue up three different pastes on the command line, and paste them in quick succession into fields of a form. Works very well, unless I accidentally mouse over Slack on the way to the form I want to paste into – then my focus-follows-mouse activates it, and it consumes one of my clipboard strings!
I have no idea why, or whether it's on purpose. I'm prepared to give it the benefit of the doubt, by assuming until further evidence that it's some unforeseen emergent consequence of the huge wobbly tower of libraries and wrappers and browsers that the desktop Slack app is built on top of. But it's not great. Some password managers will put passwords in the clipboard!
