Custom actions don't seem to be working.

I've followed the documentation as best I can, and have confirmed using a listener in a console that my embed in a webframe component is sending custom action messages via

window.parent.postMessage({
                action: {
                    type: 'resize',
                }
            }, '*');

No matter what I do though, I cannot get the action callback on the component to run

action: async (previous, action) => {
        console.log("action");
        switch (action.action) {
            case 'resize':
                console.log("resize");
                break;
        }
        return {}
    },

These snippets in my code are essentially exactly the same as the documentation. Are there any known bugs around this or have I misunderstood custom actions?

And yes, I'm and checking for "console.log()" messages in my terminal that is running the integration locally, not the browser console.

Start with the custom-actions documentation and reproduce the reported flow from the webframe component, using the supplied window.parent.postMessage call and action callback as entry points. Trace why the resize message does not reach the callback; done means the documented custom action works or the confirmed limitation and required behavior are clearly documented.