Exactly. The SD card is connected via card reader to the build system. Once the build is dumped to the SD, the Arduino deactivate the USB lines, and instead activates the lines from sd to the RPi's SD contacts and power cyles the RPi.
This should be easy to realize with a couple of transistors.
Although a robot arm for switching the SD card would also be cool :-D
This should be easy to realize with a couple of transistors.
Although a robot arm for switching the SD card would also be cool :-D