Another surprise was discovering that Ctrl-J adds a newline in Claude Code. I'm fairly certain this is a feature of the environment, not CC, but it works everywhere I've tried it. KDE Konsole on Debian.
That's because C-J IS ANSI Carriage Return. It's basically the absence of any special treatment.
It's the Carret Notation: https://en.wikipedia.org/wiki/Caret_notation