Add fail-closed Belgian training loop

backend/tests/test_belgium_training_iteration_assessment.py

@@ -0,0 +1,26 @@
+from __future__ import annotations
+
+import importlib.util
+from pathlib import Path
+
+
+SCRIPT = Path(__file__).parents[2] / "scripts" / "assess_belgium_building_training_iteration.py"
+SPEC = importlib.util.spec_from_file_location("iteration_assessment", SCRIPT)
+assert SPEC and SPEC.loader
+MODULE = importlib.util.module_from_spec(SPEC)
+SPEC.loader.exec_module(MODULE)
+
+
+def test_calibration_selection_prefers_worst_region_then_aggregate() -> None:
+    report = {
+        "sweeps": [
+            {"threshold": 0.1, "pure_empty_false_positives": 0, "aggregate": {"f1": 0.8}, "regions": {"a": {"f1": 0.2}}},
+            {"threshold": 0.2, "pure_empty_false_positives": 0, "aggregate": {"f1": 0.6}, "regions": {"a": {"f1": 0.5}}},
+        ]
+    }
+    assert MODULE.select_calibration_threshold(report)["threshold"] == 0.2
+
+
+def test_threshold_lookup_is_exact() -> None:
+    report = {"sweeps": [{"threshold": 0.25, "aggregate": {}}]}
+    assert MODULE.find_threshold(report, 0.25)["threshold"] == 0.25