This image was a good Affinity Photo learning experience for me; I messed up the post-processing of it twice — losing everything I had done to the image (hours of work) each time. The biggest take away? Within Affinity Photo, go to File => Save History With Document => Yes.
I’m so accustomed to Lightroom saving the entire post-processing history, that it never occurred to me that this would not be the default setting within Affinity Photo. Lesson learned.
UPDATE: This is not a global setting. If you want to save the post-processing history of all your images, you have to set it each and every time!