I've experimented that keychain values are not resetted after an app uninstall.
I can't find an official documentation about this behaviour.
Indeed. This behaviour is more of an artefact of the implementation rather than a designed-in feature.
Can I actively use this behaviour or it can be dropped out without notice.
The question you really have to ask is, what is my exposure if this behaviour changed? And that’s something that only you can answer. Ultimately it boils down to a risk/reward tradeoff.
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Quinn "The Eskimo!"
Apple Developer Relations, Developer Technical Support, Core OS/Hardware
let myEmail = "eskimo" + "1" + "@apple.com"