ViewModel trigger.on() callbacks are registered but never invoked

[JeppeP]

Summary

When using the ViewModel Instance API to observe triggers via trigger.on(callback), callbacks are correctly registered but never invoked when the trigger fires.

Environment

• Runtime: @rive-app/canvas v2.32.2
• Browser: Chrome 131 (also tested in Safari)
• OS: macOS

Steps to Reproduce

1. Create a .riv file with a ViewModel containing a trigger property
2. Set up a Listener in Rive that fires the trigger on click
3. In JavaScript, observe the trigger:

javascript
const rive = new Rive({
    src: 'file.riv',
    canvas: document.querySelector('canvas'),
    stateMachines: ['StateMachine'],
    autoBind: true,
    onLoad: () => {
        const vmi = rive.viewModelInstance;
        const trigger = vmi.trigger('myTrigger');
        
        console.log('callbacks before:', trigger.callbacks?.length); // 0
        
        trigger.on(() => {
            console.log('Trigger fired!'); // Never called
        });
        
        console.log('callbacks after:', trigger.callbacks?.length); // 1
    }
});

4. Click the element that should fire the trigger

Expected Behavior

The callback passed to trigger.on() should be invoked when:

• The trigger fires from a Rive Listener interaction
• trigger.trigger() is called from JavaScript

Actual Behavior

• Callback is registered (callback count increases from 0 to 1)
• Callback is never invoked
• Manually calling trigger.callbacks.forEach(cb => cb()) does work

Workaround

Currently using onStateChange to detect state transitions as a fallback for navigation triggers.

Additional Context

• The .on() method exists and accepts callbacks
• Internal callbacks array is populated correctly
• The invocation mechanism appears to be broken

Happy to provide a minimal reproduction repo if needed.