Upgrade to 4.2.3 from 4.1.4

I'm having some issues wiring up my app correctly in 4.2.3. I guess a lot has changed, but I'm not sure how to know what to correct in my modules/imports/usings.

I've fixed all the compile time issues by moving a number of my usings to imports and then also explicitly importing toybox.lang in certain cases.

However, when I run my app, code in one module fails to find other modules sitting in the same folder. I didn't previously have import statements for these, and adding them doesn't seem to work.

For example, these two files sit next to one-another.

/appconstants.mc

module AppConstants{
public const DATA_VIEW_1_ID="data_view_1";
..
}

/appconfig.mc

module AppConfig{

 public function getFieldSettings(id){
        
        var settings =[];
        if(id==AppConstants.DATA_VIEW_MAP_ID){
            settings= [Properties.getValue("map_field1"), 
                       Properties.getValue("map_field2")];
    ....
}

When I run this, the AppConstants are undefined in the AppConfig.mc file and it instantly crashes.  Do I need to reference them explicitly somehow, or with some different syntax?