Add leak-free regional YOLO dataset builder

tests/test_build_regional_yolo_dataset.py

@@ -0,0 +1,47 @@
+from __future__ import annotations
+
+import importlib.util
+from pathlib import Path
+
+import pytest
+
+
+SCRIPT = Path(__file__).resolve().parents[1] / "scripts" / "build_regional_yolo_dataset.py"
+SPEC = importlib.util.spec_from_file_location("build_regional_yolo_dataset", SCRIPT)
+assert SPEC and SPEC.loader
+module = importlib.util.module_from_spec(SPEC)
+SPEC.loader.exec_module(module)
+
+
+def test_regional_dataset_balances_contexts_and_keeps_validation_closed() -> None:
+    manifest = {"samples": [
+        {"sample_slug": "f-train", "region": "flanders", "split": "train", "context": "ribbon"},
+        {"sample_slug": "f-val", "region": "flanders", "split": "val", "context": "mixed"},
+        {"sample_slug": "w-train", "region": "wallonia", "split": "train", "context": "ribbon"},
+    ]}
+    summary = {"tiles": [
+        {"sample_slug": "f-train", "split": "train", "image_path": "/f-pos.png", "kept": True},
+        {"sample_slug": "f-train", "split": "train", "image_path": "/f-neg.png", "is_negative": True},
+        {"sample_slug": "f-val", "split": "val", "image_path": "/f-val.png"},
+        {"sample_slug": "w-train", "split": "train", "image_path": "/w.png"},
+    ]}
+    train, val, evidence = module.build(
+        summary=summary, manifest=manifest, region="flanders",
+        priority_contexts={"ribbon"}, priority_repeat=3, negative_repeat=2,
+    )
+    assert train == ["/f-pos.png"] * 3 + ["/f-neg.png"] * 2
+    assert val == ["/f-val.png"]
+    assert evidence["negative_train_entry_count"] == 2
+    assert evidence["protected_samples_in_training"] == []
+
+
+def test_regional_dataset_rejects_protected_tiles() -> None:
+    manifest = {"samples": [
+        {"sample_slug": "f-cal", "region": "flanders", "split": "calibration", "context": "ribbon"},
+    ]}
+    summary = {"tiles": [{"sample_slug": "f-cal", "split": "calibration", "image_path": "/cal.png"}]}
+    with pytest.raises(ValueError, match="protected"):
+        module.build(
+            summary=summary, manifest=manifest, region="flanders",
+            priority_contexts=set(), priority_repeat=1, negative_repeat=1,
+        )