Archive metadata utilities planning files

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: NewGraphEnvironment

planning/completed/01_metadata_utilities_findings.md

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+# Findings
+
+## Variable metadata
+
+Source of truth from `bc_climate_anomaly/app.R` and `extract_aoi_anomaly.R`:
+
+| variable | long_name | unit | anomaly_type | era5_name |
+|----------|-----------|------|-------------|-----------|
+| tmean | Mean temperature | °C | absolute | 2m_temperature |
+| tmax | Maximum temperature | °C | absolute | — (derived from hourly max) |
+| tmin | Minimum temperature | °C | absolute | — (derived from hourly min) |
+| prcp | Precipitation | % | pct_normal | total_precipitation |
+| vpd | Vapour pressure deficit | Pa | absolute | — (derived from temp + dewpoint) |
+| rh | Relative humidity | % | absolute | — (derived from temp + dewpoint) |
+| soil_moisture | Soil moisture | % | pct_normal | volumetric_soil_water_layer_1-4 |
+
+Note: `era5_name` for derived variables will be populated when `cd_fetch()` is built. For now, store the raw ERA5-Land variable names for the direct ones and NA for derived.
+
+## Periods
+
+From app.R: annual, winter (DJF), spring (MAM), summer (JJA), fall (SON). Monthly available but not default.
+
+## Cache pattern
+
+drift uses `rappdirs::user_cache_dir("drift")` — we follow the same pattern with `"cd"`.