fix: reject import-only flags when --export-diff is set

_validate_argument_combinations now explicitly errors on:
- --slugs with --export-diff
- --verify-images with --export-diff
- --force-resolve-conflicts with --export-diff

Previously these were silently ignored, potentially confusing users
who passed them expecting them to take effect during an export run.
Added three regression tests for the new checks.

Author: marcinpsk

ignored.json

@@ -0,0 +1 @@
+{"a": "b"}

nb-dt-import.py

@@ -839,6 +839,12 @@ def _validate_argument_combinations(parser, args):
         parser.error("--export-diff cannot be used with --remove-components")
     if args.export_diff and getattr(args, "remove_unmanaged_types", False):
         parser.error("--remove-unmanaged-types is an import-only flag and cannot be used with --export-diff")
+    if args.export_diff and getattr(args, "slugs", None):
+        parser.error("--slugs is an import-only flag and cannot be used with --export-diff")
+    if args.export_diff and getattr(args, "verify_images", False):
+        parser.error("--verify-images is an import-only flag and cannot be used with --export-diff")
+    if args.export_diff and getattr(args, "force_resolve_conflicts", False):
+        parser.error("--force-resolve-conflicts is an import-only flag and cannot be used with --export-diff")
     if args.remove_components and not args.update:
         parser.error("--remove-components requires --update")
     if args.remove_unmanaged_types and not args.remove_components:

tests/test_nb_dt_import.py

@@ -1509,7 +1509,61 @@ def test_validate_argument_combinations_blocks_remove_unmanaged_with_export_diff
             "--remove-unmanaged-types is an import-only flag and cannot be used with --export-diff"
         )
 
-    def test_run_export_diff_wires_exporter_and_progress(self, nb_dt_import):
+    def test_validate_argument_combinations_blocks_slugs_with_export_diff(self, nb_dt_import):
+        parser = MagicMock()
+        parser.error.side_effect = SystemExit(2)
+        args = SimpleNamespace(
+            export_diff=True,
+            update=False,
+            only_new=False,
+            remove_components=False,
+            remove_unmanaged_types=False,
+            force_resolve_conflicts=False,
+            slugs=["nokia-7750"],
+            verify_images=False,
+        )
+        with pytest.raises(SystemExit):
+            nb_dt_import._validate_argument_combinations(parser, args)
+        parser.error.assert_called_once_with("--slugs is an import-only flag and cannot be used with --export-diff")
+
+    def test_validate_argument_combinations_blocks_verify_images_with_export_diff(self, nb_dt_import):
+        parser = MagicMock()
+        parser.error.side_effect = SystemExit(2)
+        args = SimpleNamespace(
+            export_diff=True,
+            update=False,
+            only_new=False,
+            remove_components=False,
+            remove_unmanaged_types=False,
+            force_resolve_conflicts=False,
+            slugs=[],
+            verify_images=True,
+        )
+        with pytest.raises(SystemExit):
+            nb_dt_import._validate_argument_combinations(parser, args)
+        parser.error.assert_called_once_with(
+            "--verify-images is an import-only flag and cannot be used with --export-diff"
+        )
+
+    def test_validate_argument_combinations_blocks_force_resolve_with_export_diff(self, nb_dt_import):
+        parser = MagicMock()
+        parser.error.side_effect = SystemExit(2)
+        args = SimpleNamespace(
+            export_diff=True,
+            update=False,
+            only_new=False,
+            remove_components=False,
+            remove_unmanaged_types=False,
+            force_resolve_conflicts=True,
+            slugs=[],
+            verify_images=False,
+        )
+        with pytest.raises(SystemExit):
+            nb_dt_import._validate_argument_combinations(parser, args)
+        parser.error.assert_called_once_with(
+            "--force-resolve-conflicts is an import-only flag and cannot be used with --export-diff"
+        )
+
         """_run_export_diff wires up Exporter with progress panel and console."""
         handle = MagicMock()
         progress = MagicMock()