Add architecture guard for shared plain-list helper usage

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

Author: cursoragent

CONTRIBUTING.md

@@ -92,6 +92,7 @@ This runs lint, format checks, compile checks, tests, and package build.
   - `tests/test_mapping_keys_access_usage.py` (centralized key-iteration boundaries),
   - `tests/test_mapping_reader_usage.py` (shared mapping-read parser usage),
   - `tests/test_optional_serialization_helper_usage.py` (optional model serialization helper usage enforcement),
+  - `tests/test_plain_list_helper_usage.py` (shared plain-list normalization helper usage enforcement),
   - `tests/test_plain_type_guard_usage.py` (`str`/`int` guardrail enforcement via plain-type checks),
   - `tests/test_plain_type_identity_usage.py` (direct `type(... ) is str|int` guardrail enforcement via shared helpers),
   - `tests/test_polling_loop_usage.py` (`while True` polling-loop centralization in `hyperbrowser/client/polling.py`),

tests/test_architecture_marker_usage.py

@@ -18,6 +18,7 @@
     "tests/test_architecture_marker_usage.py",
     "tests/test_plain_type_guard_usage.py",
     "tests/test_plain_type_identity_usage.py",
+    "tests/test_plain_list_helper_usage.py",
     "tests/test_optional_serialization_helper_usage.py",
     "tests/test_type_utils_usage.py",
     "tests/test_polling_loop_usage.py",

tests/test_plain_list_helper_usage.py

@@ -0,0 +1,19 @@
+from pathlib import Path
+
+import pytest
+
+pytestmark = pytest.mark.architecture
+
+
+MODULES = (
+    "hyperbrowser/client/managers/extension_utils.py",
+    "hyperbrowser/client/managers/session_utils.py",
+)
+
+
+def test_extension_and_session_utils_use_shared_plain_list_helper():
+    for module_path in MODULES:
+        module_text = Path(module_path).read_text(encoding="utf-8")
+        assert "read_plain_list_items(" in module_text
+        assert "type(extensions_value) is not list" not in module_text
+        assert "type(response_data) is not list" not in module_text