Extend core type-helper guard to transport error utils

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

Author: cursoragent

CONTRIBUTING.md

@@ -90,7 +90,7 @@ This runs lint, format checks, compile checks, tests, and package build.
   - `tests/test_plain_type_guard_usage.py` (`str`/`int` guardrail enforcement via plain-type checks),
   - `tests/test_type_utils_usage.py` (type `__mro__` boundary centralization in `hyperbrowser/type_utils.py`),
   - `tests/test_polling_loop_usage.py` (`while True` polling-loop centralization in `hyperbrowser/client/polling.py`),
-  - `tests/test_core_type_helper_usage.py` (core transport/config/header/file/polling/session module enforcement of shared plain-type helper usage).
+  - `tests/test_core_type_helper_usage.py` (core transport/config/header/file/polling/session/error module enforcement of shared plain-type helper usage).
 
 ## Code quality conventions
 

tests/test_core_type_helper_usage.py

@@ -16,6 +16,7 @@
     "hyperbrowser/transport/base.py",
     "hyperbrowser/transport/sync.py",
     "hyperbrowser/transport/async_transport.py",
+    "hyperbrowser/transport/error_utils.py",
 )
 
 _PLAIN_TYPE_CHECK_PATTERN = re.compile(