I'm working on a new operating system for Nostr, it's called Verdana (a tribute to the famous Slovenian alpine ski racer Ana Drev).
Just kidding, it's only a program. But the idea is that you install...
Android's intent model is a decent reference for the action-invoking layer: the OS routes a request to whichever component declares it can handle that action. The caution from Android security writeups is that this inter-app layer is a prime attack surface, so validate every incoming action payload and export nothing by default.