This already exists. It's called noti. It's cross-platform, supports most of the same backends, and can send Slack notifications (which ntfy can't). It also has an awesome API. You can put `noti` at the start of a command or `;noti` at the end, which is what I always do. I never remember to set the notification until after I've typed the command. If you forget to set the notification and the command is already running, you can call `noti -pwatch <pid>` and set notifications after the fact. It's very well thought out.