1) Main app and extension register for app groups.
2) Main app gets a url from NSOpenPanel, makes a security scoped bookmark and saves is in NSUserdefaults with group container as the suite name.
3) Run the extension, grab the bookmark data from user defaults and resolve it. The data is not nil, but fails to resolve:
Error Domain=NSCocoaErrorDomain Code=259 "The file couldn’t be opened because it isn’t in the correct format."