This is very informative and beginner friendly write up which came be used as strategy for organizing apps in Clojure. I personally have something very similar which Redis storage used as persistent storage for storing jobs and tasks within workflow are potentially executed on diff hosts.
I would recommend to extending this topic and share your thoughts about component/mount like abstraction to the code. For example notify-sender should have credentials to connect to the services. How they are delivered? as input to the :handle-action method or as as component/mount. Interesting to learn about your approach here.
Glad to hear this was helpful, and regarding managing stuff like credentials, I like the pattern of initializing the client up front using component, mount. Then passing the client in the resource map.
The advantage over simply passing credentials is that the initializer for the client can validate itself when it loads. If you just pass the credentials and assemble the client when you try to send the message then if some variables weren't set correctly you only find out when you try to use the client at as opposed to when application starts.
Thanks for sharing!