Watching a ten-minute rule take effect means waiting ten minutes, so it tends
not to get watched. Both numbers are now env-tunable:
OMNIVOICE_ENGINE_IDLE_UNLOAD_SECONDS and OMNIVOICE_IDLE_SWEEP_SECONDS.
They are documented as a pair, because shortening only the threshold still
means waiting a full sweep interval to see it fire — which reads as a broken
sweep and sends you looking for a bug that is not there.
Unparseable values and anything below the floor are ignored with a warning
rather than honoured. A zero threshold would hand back a model the instant it
went idle and reload it for the very next request, which is worse than the
behaviour being tuned.