2-way communication with Android app (through intent?)

it still feels incorrect for Catima to contain the logic for Bangle.js' UI

Since the menus are in Bangle.js already, the UI logic is probably just sending E.showMenu({"Barcode 1": ()=>Bluetooth.println(...), "Barcode 2": ()=>Bluetooth.println(...), ... });\n so it's not too bad.

Up to you what you want to do, but if you have a separate app then you've also probably got to add extra logic in there to check that the Bangle.js app is installed and the version matches your Android app (in case at some point you need to change the protocol).

Personally, I think it would be nice to be able to use the Bangle to display barcodes without needing the phone connected (while still using the phone to actually manage everything). If that's the case then a Bangle.js app would make far more sense though - and you could use Catima to just sync the barcode data that's on the Bangle...