PropagationGridWorker hard-coded `now-2h` for run_time selection on
the conservative theory that NOAA always finishes publishing within
two hours. In practice f18 is on the mirror by HH:55–HH:00 of the
next hour, so the cron at HH:05 was always picking a cycle that was
already an hour stale.
`HrrrClient.cycle_available?/1` HEADs the wrfprsf18 idx (the slowest
file in the cycle) — a 200 means every earlier forecast hour is also
on disk. `pick_run_time/1` probes `now-1h` first; if the probe
returns true we use that cycle, otherwise we fall back to the
existing `now-2h` slot. Test hook via :hrrr_cycle_available_fn env
keeps the behaviour fully exercisable without hitting NOAA.
End-to-end: weather/score data lag drops from ~2 h to ~1 h on every
hour where NOAA delivers on time. The fallback path keeps the chain
running on slow-publish hours.