Tighten provider normalization contract and fallback semantics

tests/test_provider_adapter.py

@@ -41,3 +41,37 @@ def test_provider_registry_resolution(settings):
 
     with pytest.raises(ProviderNotFoundError):
         get_provider("does-not-exist")
+
+
+@pytest.mark.django_db
+def test_demo_provider_sync_payload_uses_normalized_shape():
+    adapter = MvpDemoProviderAdapter()
+    payload = adapter.sync_all()
+
+    assert set(payload.keys()) == {
+        "players",
+        "competitions",
+        "teams",
+        "seasons",
+        "player_stats",
+        "player_careers",
+        "cursor",
+    }
+    assert payload["cursor"] is None
+
+    player = payload["players"][0]
+    assert set(player.keys()) == {
+        "external_id",
+        "first_name",
+        "last_name",
+        "full_name",
+        "birth_date",
+        "nationality",
+        "nominal_position",
+        "inferred_role",
+        "height_cm",
+        "weight_kg",
+        "dominant_hand",
+        "is_active",
+        "aliases",
+    }