Normalize runtime secret transport whitespace

tests/test_runtime_config.py

@@ -0,0 +1,20 @@
+import os
+import unittest
+from unittest.mock import patch
+
+from user_engine.runtime import _required
+
+
+class RequiredRuntimeValueTests(unittest.TestCase):
+    def test_normalizes_secret_file_newline(self):
+        with patch.dict(os.environ, {"USER_ENGINE_TEST_SECRET": "secret-value\n"}):
+            self.assertEqual(_required("USER_ENGINE_TEST_SECRET"), "secret-value")
+
+    def test_rejects_whitespace_only_value(self):
+        with patch.dict(os.environ, {"USER_ENGINE_TEST_SECRET": " \n\t"}):
+            with self.assertRaisesRegex(RuntimeError, "USER_ENGINE_TEST_SECRET is required"):
+                _required("USER_ENGINE_TEST_SECRET")
+
+
+if __name__ == "__main__":
+    unittest.main()