Android

The best method I have found so far is Termux compiling and running the executable.
I also offered a premade executable for download, but it still must run within Termux.
Once upon a time that restriction didn't exist, but it was added years ago.

To make a simple apk, you would have to create a GUI, in Java or any other JVM (Java Virtual Machine) language such as Kotlin, then bind the .cpp's functionality to the buttons.
Using .cpp in an Android apk is possible via the NDK.

The GUI could have: Memory field or selector from dropdown list, Intention field, clickable button to create Holo-Stone files, and an integrated text editor for INTENTIONS.TXT.

Regarding iOS: it seems technically possible to also download and compile the .cpp, using an app known as "a-Shell", however it menctions that programs can only be compiled to webAssembly, probably due of Apple's iOS kernel restrictions.

To make the iOS app, it likely will require a separate implementation/version of everything, because the Repeater's license is not allowed by Apple's App Store.

Often, Android and iOS use different languages. Android uses Java, Kotlin, any JVM language, while iOS uses Objective C and Swift.
There are a few Android GUI frameworks available, but to me they seem RAM wasteful, and could perform poorly in slower phones.

Finally, one must consider a way to keep it running, a service. iOS and the App Store approvers are far more stringent in this than Android.
There is FDroid for Android, an alternate app store, only for open source apps. However, it is far less known than Google Play.