The Windows CRT reports isatty()==True for every character device, the NUL
device included, so `hermes gateway start < NUL` (stdin=DEVNULL) still took
the TTY branch: prompt_yes_no() hit EOF, defaulted to Yes and registered a
Scheduled Task — the silent install #113977 describes. Confirm isatty with
GetConsoleMode(STD_INPUT_HANDLE); a handle no console accepts is treated
like a pipe. Pipes and HERMES_NONINTERACTIVE keep their behaviour.
be0a214452