Encode Shift+Return as CSI-u across supported terminals so TUIs such as Codex can distinguish it from plain Return. This replaces Alacritty's ambiguous ESC+Return mapping, which tmux interpreted as Alt+Return and used to split panes, while preserving Alt+Shift+Return as CSI-u for tmux's M-S-Enter binding.
The following options are no longer recognized by Kitty and caused warnings during startup:
window_padding_height
show_window_resize_notification
single_instance
They have been removed to keep the configuration compatible with current Kitty versions.
David Heinemeier Hansson