fix(exchange): isolate concurrent connection checks

tests/apps/exchange/test_service_units.py

@@ -505,6 +505,27 @@ class ExchangeConnectionServiceUnitTest(TestCase):
         self.assertEqual(connections_mock.databases[alias]["PASSWORD"], "secret")
         self.assertNotIn(alias, storage.__dict__)
 
+    def test_configure_alias_uses_unique_alias_for_unsaved_connection(self):
+        connection = ExchangeConnection(
+            server="127.0.0.1",
+            port=5432,
+            username="postgres",
+            password="secret",  # noqa: S106
+            database_name="target_db",
+            schema_name="public",
+        )
+
+        first_alias = ExchangeConnectionService._configure_alias(connection)
+        second_alias = ExchangeConnectionService._configure_alias(connection)
+
+        try:
+            self.assertNotEqual(first_alias, second_alias)
+            self.assertTrue(first_alias.startswith("exchange_target_"))
+            self.assertTrue(second_alias.startswith("exchange_target_"))
+        finally:
+            ExchangeConnectionService._cleanup_alias(first_alias)
+            ExchangeConnectionService._cleanup_alias(second_alias)
+
     def test_validate_schema_exists_raises_when_schema_missing(self):
         cursor = MagicMock()
         cursor.fetchone.return_value = None