Yep, this makes sense. I’ve accepted a feature to make the query string from the URL that opened a WebApp session available to the app, including during App.Opening: https://feedback.objo.dev/feature/1611
The proposed API is App.Session.InitialQueryString, plus InitialQueryParameter(name) for one decoded value and InitialQueryParameters(name) for repeated values. That would let an app handle a link such as /?document=42 without setting up a separate HTTP request handler. The values would stay fixed for that session across reconnects.