Perform action before script compilation

Hi guys, we are trying to create an editor script that will copy over some required DLLs from a shared folder automatically if they are missing (or update them if they are out of date).

We tried using [InitializeOnLoad], but the code only gets run if the rest of the codebase compiles, which of course it doesn't because the DLLs are required for compilation.

I've tried subscribing to the EditorApplication.update callback but that doesn't seem to work either.

Seems like a bit of a chicken & egg problem. Is there any way to achieve this?

Thanks!