Can we reset CSI u mode on client disconnect? via

[Johannes Altmanninger]

Some terminals support CSI u style encoding of keystrokes, typically via
the Kitty keyboard protocol[1].

Program wishing to receive this encoding need
to send a sequence like "CSI > 5 u" to enable it.

Imagine a process tree like

	xterm -> bash -> ssh -> foo

where foo is any program that enables CSI u mode (such as a newfangled shell
or text editor).

If the network connection drops, CSI u mode will remain active in xterm,
which means that keystrokes like Control+p will be sent to bash as CSI u
escape sequences, which bash will likely not be able to decode.

Can we make ssh reset CSI u mode when the connection drops? (by sending
"CSI = 0 u" for example) It should not be needed on a graceful disconnect
although it doesn't harm either.  (Or better, record the state before running
the child process and restore it on exit)

ssh's parent process is typically a shell; if that shell uses CSI u mode,
it should already re-enable CSI u whenever an external command finishes.

Find more discussion here[2].

[1]: https://sw.kovidgoyal.net/kitty/keyboard-protocol/#progressive-enhancement
[2]: https://github.com/kovidgoyal/kitty/issues/7603