I assume that there is control character after carriage return that deletes everything from there to the EOL, so this do not break copy functionality or "go to EOL" shortcuts.
Oh, I just saw your reply after posting my own, though you beat me to it by quite some margin of time. That's correct, fish sends ^[[K to clear to the EOL after correctly setting the cursor position via this hack to erase any evidence of the hack and for posterity of your ptty contents.
ComputerGuru|5 years ago
JdeBP|5 years ago
* https://unix.stackexchange.com/a/586458/5132