Add architecture guard against isinstance str/int checks

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

Author: cursoragent

CONTRIBUTING.md

@@ -86,7 +86,8 @@ This runs lint, format checks, compile checks, tests, and package build.
   - `tests/test_makefile_quality_targets.py` (Makefile quality-gate target enforcement),
   - `tests/test_pyproject_architecture_marker.py` (pytest marker registration enforcement),
   - `tests/test_architecture_marker_usage.py` (architecture marker coverage across guard modules),
-  - `tests/test_readme_examples_listing.py` (README example-listing consistency enforcement).
+  - `tests/test_readme_examples_listing.py` (README example-listing consistency enforcement),
+  - `tests/test_plain_type_guard_usage.py` (`str`/`int` guardrail enforcement via plain-type checks).
 
 ## Code quality conventions
 

tests/test_architecture_marker_usage.py

@@ -16,6 +16,7 @@
     "tests/test_makefile_quality_targets.py",
     "tests/test_pyproject_architecture_marker.py",
     "tests/test_architecture_marker_usage.py",
+    "tests/test_plain_type_guard_usage.py",
 )
 
 

tests/test_plain_type_guard_usage.py

@@ -0,0 +1,22 @@
+import re
+from pathlib import Path
+
+import pytest
+
+pytestmark = pytest.mark.architecture
+
+
+_ISINSTANCE_PLAIN_TYPE_PATTERN = re.compile(
+    r"isinstance\s*\([^)]*,\s*(?:str|int)\s*\)"
+)
+
+
+def test_sdk_modules_avoid_isinstance_str_and_int_guards():
+    violations: list[str] = []
+    for module_path in sorted(Path("hyperbrowser").rglob("*.py")):
+        module_text = module_path.read_text(encoding="utf-8")
+        for line_number, line_text in enumerate(module_text.splitlines(), start=1):
+            if _ISINSTANCE_PLAIN_TYPE_PATTERN.search(line_text):
+                violations.append(f"{module_path}:{line_number}")
+
+    assert violations == []