Can someone tell me how I can debug inside of the /alfresco/s/slingshot/doclib/action/file/node/ code? I can't find it either in the java or in the javascript.
it appears there is some kind of permission issue at work. 403 is the status code for FORBIDDEN and usually that is the result of an access denied evaluation of permissions.
You could set the logger org.alfresco.repo.security.permissions.impl.acegi.ACLEntryVoter to DEBUG to find out where you have an access denied situation. Beware that this will generate A LOT of log output, so it's best to check in isolation…