A 4-char locator covers ~70 km × 100 km, which dwarfs HRRR's 3 km
native cell and any midpoint we'd derive for the calibration corpus.
Storing those samples gives the recalibrator geometry that's
indistinguishable from noise.
fetch_grid/2 now returns {:error, {:short_grid, key, grid}} for any
locator under 6 chars after Maidenhead validation. The spot is
dropped before it reaches the aggregator, so neither pskr_spots_hourly
nor pskr_calibration_samples ever see it.
Graham McIntire
1a3dc4fa0a