Thanks, Horemvore.
I saw the <Unavailable> tag, but convinced myself that it must be ignored or inactive, since the Projects still showed in the Tech Tree. Disabling the tag restores and activates the Projects, thereby avoiding the Idle Colony loop.
I'll report the bug and ask about AI Research and Aid Economy, since it seems likely that they are supposed to replace the Projects (and prevent the Idle Colony loop), but they're nowhere to be found in my (recent re-) install.