Fix Shift+Return terminal encoding

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.

config/alacritty/alacritty.toml

@@ -21,7 +21,8 @@ decorations = "None"
 bindings = [
 { key = "Insert", mods = "Shift", action = "Paste" },
 { key = "Insert", mods = "Control", action = "Copy" },
-{ key = "Return", mods = "Shift", chars = "\u001B\r" },
+# Send Shift+Return as CSI-u so TUIs can distinguish it from Return without treating it as Alt+Return.
+{ key = "Return", mods = "Shift", chars = "\u001B[13;2u" },
 # Legacy encoding sends Alt+Shift+Return the same as Alt+Return; send CSI-u so tmux can match M-S-Enter.
 { key = "Return", mods = "Alt|Shift", chars = "\u001B[13;4u" }
 ]

config/foot/foot.ini

@@ -17,3 +17,9 @@ blink=no
 clipboard-copy=Control+Insert Control+Shift+c XF86Copy
 primary-paste=none
 clipboard-paste=Shift+Insert Control+Shift+v XF86Paste
+
+[text-bindings]
+# Send Shift+Return as CSI-u so TUIs can distinguish it from Return.
+\x1b[13;2u=Shift+Return
+# Send Alt+Shift+Return as CSI-u so tmux can match M-S-Enter.
+\x1b[13;4u=Mod1+Shift+Return

config/ghostty/config

@@ -25,6 +25,8 @@ shell-integration-features = no-cursor,ssh-env
 # Keyboard bindings
 keybind = shift+insert=paste_from_clipboard
 keybind = control+insert=copy_to_clipboard
+# Send Shift+Enter as CSI-u so TUIs can distinguish it from Enter.
+keybind = shift+enter=csi:13;2u
 # Legacy encoding sends Alt+Shift+Enter the same as Alt+Enter; send CSI-u so tmux can match M-S-Enter.
 keybind = alt+shift+enter=csi:13;4u
 keybind = super+control+shift+alt+arrow_down=resize_split:down,100

config/kitty/kitty.conf

@@ -13,6 +13,8 @@ confirm_os_window_close 0
 # Keybindings
 map ctrl+insert copy_to_clipboard
 map shift+insert paste_from_clipboard
+# Send Shift+Enter as CSI-u so TUIs can distinguish it from Enter.
+map shift+enter send_text all \e[13;2u
 # Kitty legacy encoding sends Alt+Shift+Enter the same as Alt+Enter; send CSI-u so tmux can match M-S-Enter.
 map alt+shift+enter send_text all \e[13;4u