Gate finding B01 #1 (2c + quality): since api_server (/v1) runs now ride
the cron drain floor, the docstrings and comments for
parse_cron_drain_timeout, _load_cron_drain_timeout,
_get_cron_drain_timeout, the DEFAULT_GATEWAY_CRON_DRAIN_TIMEOUT comment,
cli-config.yaml.example and the messaging guide still called it a
cron-only floor. Say it covers /v1 runs too, that 0 opts them out as
well, and why: an interrupted /v1 run fails its waiting caller.
adc55b6a71