Constant FISH 

pub const FISH: &str = r"
function _forge_prompt --on-event fish_prompt
  set -l ret $status
  if set -q _forge_cmd_running
    printf '\033]133;D;%s\007' $ret
    set -e _forge_cmd_running
  end
  printf '\033]133;A\007\033]133;B\007'
end
function _forge_preexec --on-event fish_preexec
  set -g _forge_cmd_running 1
  printf '\033]133;C\007'
end
";

The fish integration: the fish_prompt and fish_preexec events.