Running a cleanup of icloud desktop on load
Okay, I managed to work out the problem. Unfortunately, it was the usual culprit: The heavy privacy permissions system MacOS has been relying on since Catalina!
Since I was running the command from zsh in order to effectively get the correct user context for relative directories I had to the following:

Now, I am concerned that these somewhat defeats the purpose of this hardened security. I would really appreciate any information as to how it might be best to allow this to run without opening up my whole OS to zsh... Perhaps launchd or launchctl? I fear those are still quite open.