You missed the main holy grail requirement: open source.
Nothing closed source can be trusted.
Nothing closed source can be trusted.
But this would require some kind of effort from project maintainers.
or download from a source you trust and compare hash from another trustworthy source. just like anything you download. unless you run gentoo, but then how do you trust your sources, etc
and if you have a closed source phone os that only allows to install from their store... well you have to learn to crawl before you walk.
A) exact compilation settings
B) hash checksums for everything, including the resulting binaries
You probably can't do this on iOS, but on Android you can have a third party app monitoring the changes, or simply disabling the automatic updates altogether.