Test extension missing-key control placeholder semantics

Co-authored-by: Shri Sukhani <shrisukhani@users.noreply.github.com>

Author: cursoragent

tests/test_extension_utils.py

@@ -163,6 +163,14 @@ def test_parse_extension_list_response_data_missing_key_normalizes_control_chara
         parse_extension_list_response_data({"bad\tkey": "value"})
 
 
+def test_parse_extension_list_response_data_missing_key_preserves_control_placeholders():
+    with pytest.raises(
+        HyperbrowserError,
+        match="Expected 'extensions' key in response but got \\[\\?\\?\\] keys",
+    ):
+        parse_extension_list_response_data({"\n\t": "value"})
+
+
 def test_parse_extension_list_response_data_missing_key_handles_unprintable_keys():
     class _BrokenStringKey:
         def __str__(self) -> str: