I have noticed that some menu items always show up in the HUD regardless of which application is focused (e.g. Messages > Chat), but others only show up when the application is focused (e.g. Chat > New Conversation). What controls this behavior and how easy is it to add new global actions that target a specific application (e.g. I want to be able to create a new conversation from anywhere).
For HUD, the rule seems to be, you can do something with only those things that you can see.
You can ALWAYS see app-indicators, so all menu items related to these are always available.
But for other applications, the menu items are available only when you are 'in' that application.