Jesse suggested that even the few seconds I was getting the keyboard recognized over USB would be enough to flash the firmware again with avrdude. It was! I just had to get the correct port.
- I have Arduino IDE open while I plug in the keyboard (holding prog key).
- Check the ports drop down in Arduino repeatedly to find the port, which only shows for a second.
- The port is /dev/ttyACM0
- Get this command ready to go in the console:
avrdude -patmega32u4 -cavr109 -D -P /dev/ttyACM0 -b57600 -Uflash:w:atmega32u4_firmware.hex:i - Plug in keyboard again (holding prog key) and run command immediately.
- Found programmer. Writing flash. Reading flash. Success!
Typing this on the keyboard right now! 