Tip: if you prefix your command by a space in bash (and maybe other shells) that command doesn't get recorded in history.

Don’t go doing this and expecting it’s the default behavior. It’s not. Your bash session must have set, at minimum:

   HISTCONTROL=“ignorespace”

Issue is /proc/$pid/environ if enabled. Envvars are visible just like args. I think there are other ways to recover if on same uid.