Marco S Hyman
This said, the porcupine in my home directory seems to be a red herring:I don’t know if this has anything to do with your issue.
One difference between a sandboxed and non-sandboxed app is that the “home directory” in a sandboxed app is inside the application container, not the current users home directory.
~/ ==> non-sandboxed home directory
~/Library/Containers/com.example.appid/Data/ ==> sandboxed home directory
You will not be able to create/access anything outside of the sandbox container without going through Powerbox or adding appropriate entitlements.