"I just asked Gemini, and it turns out that Mossad can steal my data anyways".

- An app without the INTERNET permission will crash the moment you try to access the internet. It's like a rite of passage of every android developer with every new project, you forgot the permission.

- Launching an Intent is EXTREMELY visible. It opens a full on browser. It's limited to a GET with a dedicated URL, so what are they going to do, stuff your data in query params ?

- Even in the case of another app being installed that would silently receive this intent and not pop an activity, you need a different app. It cannot be an activity added by the same package.

- Loading a Chrome Custom Tab opens a whole ass browser in front of you, think you're going to miss it ?

- Shared user IDs also require two different app installations and you cannot declare multiple. You also cannot have sharedUserId if you do not sign the apps with the same key. you cannot sharedUserId with Facebook, you need once again a dedicated app installation.

- A ContentProvider needs a dedicated permission on the writing app AND on the reading app, which is once again very visible.

I'll add more to your list: an app can request to write a file inside your downloads folder, and another one can show a popup asking you to open it! And if someone shows up with a hammer at your door, he can also hit your fingers really hard to make you tell him the data.

Android apps are, by default, very well isolated. INTERNET is a permission like any other, just not surfaced as a dangerous one (like permanent access to your background location would be), or a runtime one (like access to your current location while the app is in foreground)