Well, the problem remains unsolved, after all. Today I shot some bird photos, imported into mac Photos, created a new smart folder for RAW images, and verified they were CR2. I then opened AP, navigated to the RAW folder in Photos, opened an image, and it opened in the photo persona as a jpeg.
Hmm. I then went to the AP media browser, navigated to the same image, opened it, and it opened in the photo persona as a jpeg. So, I did a little investigating again. As you will see in the attached screenshot, Photos correctly shows the image as CR2. The AP media browser shows it as a jpeg. I then right-clicked the thumbnail in the AP media browser and selected "show in finder" - which displayed the image as a jpeg in a mystery folder. Now none of the raw files are showing as CR2 in the AP media browser.
So, I then exported the CR2 image from Photos to a desktop folder; in AP navigated to File>Open and to the image in the desktop folder which was displayed as CR2 and opened in the develop persona. I am unable to navigate to the desktop folder in the AP media browser.
Somehow, somewhere the CR2 images are also on my Mac somewhere in mystery folders as jpegs. Which explains why yesterday I was seeing what I was certain were CR2s as jpegs. However, yesterday I could find the CR2 images in Photos with the AP media browser. Today - no. Nor is AP>File>Open seeing the Photos images as CR2. Now AP only recognizes the CR2 if I export it from Photos.
I won't rule out that this is still user error; but, I'm thinking it's a bug somewhere.