That proto frame goes way back. I shot this photo of it in the early fall of 2023. Sorry for poor quality. The obvious heel rub and linkage swap-out (on your more current photo) shows it's seen a lot of hours. The guy riding it started working for a different bike company, so he may have offloaded this one to another industry friend. At the time, I was thinking it was maybe a Diamondback prototype that got canceled/never saw the light of day. He was fairly open with it; it was spotted at local Seattle area watering hole(s), etc.