Using a keyboard to send Volume Up signal to confirm flash on device without volume rocker?
Fastboot is implemented in bootloader (like aboot or LK) i.e. in boot chain it loads even before the first process (kernel) of main OS. It has its own very minimal kernel which doesn't recognize any hardware components (even on device) except those necessarily required at this stage (processor, memory, display, flash storage etc.). Communication with PC over USB is only acceptable through fastboot protocol which doesn't have support to accept keystrokes or other input events (at least I never heard of such functionality). So it won't receive your