Add hard-negative balanced YOLO tile export

backend/tests/test_sprint130_operator_yolo_tile_dataset.py

@@ -64,6 +64,7 @@ def test_operator_yolo_tile_dataset_export_help_does_not_require_gis_dependencie
     assert "--tile-size" in result.stdout
     assert "--stride" in result.stdout
     assert "--negative-keep-ratio" in result.stdout
+    assert "--background-negative-repeat" in result.stdout
 
 
 def test_iter_tile_windows_covers_edges_without_duplicates() -> None:
@@ -93,3 +94,32 @@ def test_negative_tile_keep_is_deterministic_and_ratio_bound() -> None:
     assert 1 <= sum(first) <= 25
     assert all(all_kept)
     assert not any(none_kept)
+
+
+def test_background_negative_repeat_only_applies_to_training_background_tiles() -> None:
+    module = load_tile_exporter()
+
+    assert module.background_negative_repeat_count(
+        is_negative=True,
+        sample_role="background_candidate",
+        split="train",
+        background_negative_repeat=4,
+    ) == 4
+    assert module.background_negative_repeat_count(
+        is_negative=True,
+        sample_role="background_candidate",
+        split="val",
+        background_negative_repeat=4,
+    ) == 1
+    assert module.background_negative_repeat_count(
+        is_negative=False,
+        sample_role="background_candidate",
+        split="train",
+        background_negative_repeat=4,
+    ) == 1
+    assert module.background_negative_repeat_count(
+        is_negative=True,
+        sample_role="reference",
+        split="train",
+        background_negative_repeat=4,
+    ) == 1