I have an Action, and I'd like to give it two inputs: a select input for "type of thing" and then a second select that's dynamically populated with record IDs based on the type of thing selected in the first select.

This is very similar to the example shown at https://docs.avohq.io/2.0/stimulus-integration.html#custom-stimulus-controllers with the important difference that it's on an action rather than on a resource controller.

I think the closest thing I could do would be to create a model / resource that encapsulates the relationship, and switch from using an action to using the create page for that new model / resource. Then I could apply the strategy given in that example.

1. add the same stimulus integration from resources to actions. (it might not be that difficult)

2. add the ability to use a custom partial for an action. so you can totally override whatever is displayed in the modal