Add Belgium and North Sea coverage foundation

docs/API_CONTRACTS.md

@@ -935,6 +935,49 @@ Read simplified job status payload.
 
 ## Provider registry
 
+The legacy Sprint 7 provider registry remains the exact
+`grb|osm|manual|fixture` import abstraction. National and maritime source
+authority is exposed separately so adding official source families cannot
+silently change that import contract.
+
+### GET `/api/v1/external/coverage/catalog`
+
+Returns the normalized Belgium and Belgian North Sea theme vocabulary, legal
+coverage zones, allowed availability states and audited source contracts.
+Every source includes authority, native layers, geometry types, acquisition
+mode, source URL, attribution, licence and limitation text.
+
+Allowed result states are exactly:
+
+- `operational`: a matching `ready` Dataset is materialized in the project;
+- `partial`: the governed integration exists but matching project data is
+  absent or incomplete;
+- `not_configured`: an audited source has no operational adapter;
+- `unsupported`: no audited contract supports the theme in that zone.
+
+### POST `/api/v1/external/coverage/resolve`
+
+Resolves a user-drawn EPSG:4326 bbox against persisted national and maritime
+Areas. Cross-region and land/sea selections remain split by zone.
+
+```json
+{
+  "project_id": "uuid",
+  "bbox": {
+    "minx": 2.65,
+    "miny": 51.05,
+    "maxx": 2.85,
+    "maxy": 51.20
+  },
+  "themes": ["buildings", "surface_water", "bathymetry"]
+}
+```
+
+The response returns `intersected_zones`, `outside_supported_scope`, one item
+per zone/theme combination, matching source names and IDs of actually
+materialized Datasets. An empty `themes` list requests the complete normalized
+vocabulary. Unknown themes fail with `COVERAGE_THEME_UNSUPPORTED`.
+
 ### GET `/api/v1/external/providers`
 
 Returns all configured provider capability descriptors.