Accept official Statbel geometry date format

backend/tests/test_sprint227_statbel_population_preflight.py

@@ -266,6 +266,13 @@ def test_preflight_reports_bounded_topology_repairs(tmp_path: Path) -> None:
     assert result.geometry.payload["features"][0]["geometry"]["type"] == "Polygon"
 
 
+def test_preflight_accepts_official_slash_geometry_date(tmp_path: Path) -> None:
+    result = validate(tmp_path, geometry_content=geometry_archive(date="2025/01/01"))
+
+    assert len(result.geometry.payload["features"]) == 3
+    assert result.manifest["import_eligible"] is True
+
+
 @pytest.mark.parametrize(
     ("population_kwargs", "error_code"),
     [
@@ -292,6 +299,7 @@ def test_preflight_rejects_population_contract_breaks(
     [
         ({"crs": "EPSG:4326"}, "STATBEL_GEOMETRY_CRS_REJECTED"),
         ({"date": "2026-01-01"}, "STATBEL_GEOMETRY_DATE_MISMATCH"),
+        ({"date": "2025/13/01"}, "STATBEL_GEOMETRY_DATE_MISMATCH"),
         ({"municipality_mismatch": True}, "STATBEL_JOIN_MUNICIPALITY_MISMATCH"),
     ],
 )