Is doing file io (

File.exists()

) fine at configuration time?

Yes

If you can avoid it, you want to avoid it though, as it becomes a configuration cache input. If you need the information to decide whether to register a specific task or similar, it is fine of course and proper, that it is a cc input.

Its just passing proguard file to AGP by convention (if its in correct place and named correctly it will get autopicked up with no extra config) So..idk? Can I avoid it? Or bad idea?

Not really familiar with AGP, but sounds like it might not be possible to avoid.

unless AGP quietly no-ops when passed a non-existent file, I'd say it's fine

it used to no-op, but now agp9 throws an error

yeah, then the existence check makes sense and doesn't violate any Gradle best practices