That's not the actual sensor that is "beveled".¹ It is the front of the filter stack that sits in front of the actual sensor. The beveled edge is in an area outside of the coverage area of the actual sensor that is a few mm behind it. Since the beveled area is not part of the imaging sensor nor is it in the light path of the image projected onto the sensor, it's pretty much the same as any other part inside the camera's light box.

Even digital cameras without low pass filters still almost always have a cover glass and IR filter.

All cameras and lenses have dust in them before they leave the factory. The best one can do is to minimize it and remove it when it does get in the optical path close enough to the sensor to have an impact. "Self-cleaning" sensors will shake a lot of the loosest dust off the front of the cover glass. Most people who obsessively clean their sensor all of the time probably have more dust inside their camera's light box than the rest of us because they have the front of the camera open way more often for longer periods of time than the rest of us do.

¹ Although I've not examined a Sony α7 or α9 sensor closely, my hunch is that what looks like a bevel is actually just the different refractive/reflective properties of the cover glass on the edges that sit outside the actual coverage area of the sensor behind it.