This was a near-miss. After hiking to the top of the cliff, I attached my personal tether (double-length nylon sling girth-hitched to harness hard points) to one of the anchor bolts. I proceeded to fix a rope to both anchor bolts so that I could top-rope solo the route. I removed my GriGri from my gear loop and attached it to the strand running down the route, then clipped it to the midpoint of my tether in anticipation of extending the rappel. After cinching the GriGri up the rope as far as it could go, I was unable to get my weight transferred to it (my tether was too short and the Big Knot was too low). My first instinct was to disengage by personal tether and trust that I had rigged the GriGri correctly. I reconsidered this at the last moment and added an alpine draw from my tether to the other anchor bolt. I then removed the first locking carabiner (that had caused my tether to be too short to properly test the rappel setup). I then transferred my weight to the GriGri, which engaged, but also revealed that I had only clipped one plate of the GriGri to myself. The swiveling plate of the GriGri swiveled as the GriGri cam engaged to reveal the inner workings of the GriGri.
I quickly reattached my locking carabiner (so that I was tethered to both anchor bolts), closed the GriGri, and re-clipped it. After that, things were back to normal and the day continued without incident.