Here's the video -- it is a noisy thing with both the CNC router and the small shop vacuum running:
You can see when the error occurred at about 10:50 -- I first thought it was a slippage on the Z-axis screw (which you can see me adjusting back upwards after pausing the g-code controller program) but it keeps plunging in. I was hoping that the pieces would be usable, but the resulting X-axis slippage meant that it ran off the back edge of the sheet...