feat: complete governed Walloon coverage sources

backend/README.md

@@ -1599,6 +1599,40 @@ Datasets. A full-Flanders raster request remains blocked by the same 60 km and
 `Gemeente ...` as `coverage_scope=municipality`; regional Area clipping is
 stored as `bounded_selection`.
 
+## Walloon WALOUS land cover and flood hazard
+
+The Wallonia map flow uses bounded PICC vector products, the queryable legal
+SPW flood-hazard polygon layer and provisioned official WALOUS land-cover
+rasters. Provision the 2020 and 2023 source editions once in the persistent
+storage mount:
+
+```bash
+docker exec geointel python /app/scripts/provision_walous_sources.py \
+  --years 2020 2023 \
+  --destination /app/storage/source-cache/walous
+```
+
+The provisioner verifies advertised archive sizes, safe ZIP structure,
+EPSG:3812, one band, 1 m cells, class values 1-11 and SHA-256 checksums. It
+does not run at application startup. `GET .../datasets/walous/products`
+therefore reports `source_not_provisioned` until both source files exist.
+
+For a bounded Walloon selection the browser persists the latest edition and
+all other configured comparable editions. `POST .../raster/walous/select`
+returns cell-area hectares; the temporal API compares the same semantic metric
+keys for 2020 and 2023. WALOUS is land cover, not legal land use, ownership,
+tree count, timber volume or water volume.
+
+Settings: `WALOUS_ENABLED`, `WALOUS_SOURCE_DIR`,
+`WALOUS_ANALYSIS_RESOLUTION_M`, `WALOUS_MAX_SIDE_M` and
+`WALOUS_MAX_PIXELS`. The SPW flood polygon adapter uses
+`SPW_FLOOD_HAZARD_ENABLED` and `SPW_FLOOD_HAZARD_MAPSERVER_URL`.
+
+The official Walloon 2021-2022 DTM is currently not an implicit runtime asset:
+the published 1 m whole-region artifact is about 41 GB and the 0.5 m INSPIRE
+artifact about 213 GB. A later operator capacity plan must define storage,
+partitioning and refresh before it can be called operational.
+
 Provision the official DOV soil polygons for Mol through the existing vector
 upload path: