As an accomplished Android developer fluent in Java, I can certainly deliver the WebView app you require and with the added functionality of OneSignal for push notifications. Having built numerous WebView apps in the past, I'm no stranger to integrating external features into a web application. In fact, I'm comfortable implementing device ID unique and saving this information locally or using some device ID techniques, which aligns perfectly with your requirements of appending the device UUID parameter at the end of the URL.
To further enhance your user experience, I understand how crucial it is to set this device ID as the external ID in OneSignal. My proficiency extends beyond the WebView aspect of your project; I am also well-versed with this particular SDK and can seamlessly integrate it into our app.
In addition to meeting your specific requirements, my approach as a technology partner is to fully grasp and execute on your business objectives. Additionally, my expertise with Firebase and RESTful APIs will lend stability to your app's backend while helping it shine on the front end. Ready when you are, let’s construct something impactful together!