plugin inspector not working for OSX bundle

I’ve got the world’s simplest test plugin in C compiling to a bundle in xcode and included in my Unity project, and it works like a charm when running in the Unity IDE or when compiled to an OSX Desktop app.

but I’d like not to include this file in other builds, like WebGL or iOS.
however when i select the .bundle in the project navigator (the .bundle is actually a folder), the inspector panel keeps displaying whatever was most recently shown - scene, image, .CS source, whatever.

i’m sure i’m missing something obvious.

derp - i need to select it in the right-hand panel of the project-navigator, not in the left-hand panel.