How to read state in onStart

As you said correctly symbol numbers are not constants.

If I am stuck on a function, best address is most often the API documentation:

https://developer.garmin.com/connect-iq/api-docs/Toybox/Application/AppBase.html#onStart-instance_function

There you see how the symbols are named.

Try this:

function onStart(state as Dictionary?) as Void {
        System.println("App onStart");
        if (state != null) {
            System.println("full state: " + state.toString());
            System.println("resume: " + state.get(:resume ));
            System.println("launchedFromGlance: " + state.get(:launchedFromGlance));
            System.println("launchedFromComplication: " + state.get(:launchedFromComplication ));
        }
    }

As the documentation writes. state is a dictionary with the keys :resume, :launchedFromGlance and :launchedFromComplication. Use the method get from a Dictionary to retrieve its values.

It is important to check if the state is null or not. If I start the app without a GlanceView in the simulator, the state is null. So you can conclude that if the state is null, it is not launched from glance.