Harden Statbel population import compatibility

backend/README.md

@@ -1043,6 +1043,36 @@ third imports the Departement Omgeving 10 m forest class for 2013, 2016, 2019,
 API/DatasetService flow and retain fetched artifacts in persistent operator
 storage. They never run on app startup.
 
+Every newly fetched or `--force` rebuilt Statbel population edition now passes
+`statbel_population_preflight.py` before a derived GeoJSON can reach the
+upload API. The operator retains both official ZIPs, writes an atomic
+preflight manifest and verifies the source and derived SHA-256 values again at
+upload time. A passed preflight does not replace an existing Dataset.
+
+The preflight can also be run without downloads or database mutation against
+already staged official artifacts:
+
+```bash
+docker exec geointel python /app/scripts/statbel_population_preflight.py \
+  --year 2025 \
+  --layout new \
+  --scope kempen-transport-region \
+  --population-archive /tmp/OPENDATA_SECTOREN_2025_NEW.zip \
+  --population-url https://statbel.fgov.be/sites/default/files/files/opendata/bevolking/sectoren/OPENDATA_SECTOREN_2025_NEW.zip \
+  --geometry-archive /tmp/sh_statbel_statistical_sectors_31370_20250101.geojson.zip \
+  --geometry-url https://statbel.fgov.be/sites/default/files/files/opendata/Statistische%20sectoren/sh_statbel_statistical_sectors_31370_20250101.geojson.zip \
+  --baseline-snapshot /app/storage/operator-data/regional-timeseries/kempen-transport-region/population/kempen_transport_region_statbel_population_2024.geojson \
+  --output /app/storage/operator-evidence/statbel-population/2025-kempen.preflight.json
+```
+
+The command exits non-zero and emits a stable `error_code` when source
+identity, archive safety, schema, CRS, geometry, join, total reconciliation,
+scope coverage or the default 5% annualized population-change review limit
+fails. `ZZZZ` rows are reconciled as official unlocated population but remain
+excluded from spatial metrics. The 2025 REDEGEO contract deliberately compares
+explicit municipality fields; it does not assume that `CD_SECTOR` still starts
+with the current `CD_REFNIS` after municipal mergers.
+
 Historical land-use work can be bounded explicitly:
 
 ```bash