Good news! Back in business. Very straightforward to fix a surprising failure. Looked much worse than it was. Used pliars and a needle-nose tweezers.
I think I know what happened. The print that failed had support inadvertently turned off. The print must have broken off and blocked the nozzle, forcing the plastic back up into the chamber with the heated block.
I re-did the gcode file and re-ran the print, and it succeeded. Thank you very much for the pointer to the correctly defined problem. I was pretty sure something had broken above the nozzle, but it did not.