[pugz]

(You're probably already much more familiar with it than I am, but if not:)

Your example of the file open dialog box is identical to what Apple did on MacOS when they implemented sandboxing. Rather than using regular paths in NSString objects, they return you an NSURL with a "security scope" - a capability. These can be saved and reused across process terminations.

The docs provide useful information how they are used: https://developer.apple.com/documentation/foundation/nsurl