"ST" in ANSI Escape Responses is Ambiguous/Inconsistent

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• iTerm2 version: 3.4.15
• OS version: Mojave
• Attach ~/Library/Preferences/com.googlecode.iterm2.plist here (drag-drop from finder into this window)

com.googlecode.iterm2.plist

I know the Proprietary Escape Code documentation says:

ST means either BEL (hex code 0x07) or ESC \\.

Which is fine on input (The "Be liberal in what you accept" part of Postel's Law) but I find it frustrating that the escape sequences that are reported sometimes use ^G and sometimes use ^[\ — which seems to violate the "Be conservative in what you produce" part... And I haven't found any way of figuring out in advance which ones will use which; though it's certainly possible I just haven't looked in the right place, yet! «grin»

For example, Report Foreground/Background Colors (OSC 4) returns ^G:

^[]4;-1;rgb:fffe/ffff/ffff^G

Whereas the escape sequence that's returned from Report Cell Size uses ^[\:

^[]1337;ReportCellSize=22.0;10.0;1.0^[\

The former I can read from bash:

prompt% printf "\e]4;-1;?\a"; read -s -r -d $'\a'; cat -v <<< "$REPLY" ^[]4;-1;rgb:fffe/ffff/ffff

The latter, however, is trickier, since even if I DO know which delimiter to look for, it's now two characters wide:

### If we fear the payload could ever contain a non-terminal backslash...
reportCellSize() {
  local _buffer

  printf "\e]1337;ReportCellSize\a" >/dev/tty;

  while read -s -r -d \\ </dev/tty; do
    _buffer+="$REPLY\\"

    # This is the same as `[[ condition ]] && break`
    # but it doesn't die under `set -e`...
    ! [[ $_buffer =~ $'\e\\'$ ]] || break
  done

  if [[ $_buffer =~ ^$'\e'\]1337\;ReportCellSize=(.*)\;(.*)\;(.*)$'\e'\\$ ]]; then
        echo "height=${BASH_REMATCH[1]}"
        echo "width=${BASH_REMATCH[2]}"
        echo "scale=${BASH_REMATCH[3]}"

  elif [[ $_buffer =~ ^$'\e'\]1337\;ReportCellSize=(.*)\;(.*)$'\e'\\$ ]]; then
        echo "height=${BASH_REMATCH[1]}"
        echo "width=${BASH_REMATCH[2]}"

  else  printf "Invalid CellSize: %q\n" "$_buffer" >&2
        return 1
  fi
}

Thanks for any clarification you can provide! :-D