Add architecture guard for python3 command consistency

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

Author: cursoragent

CONTRIBUTING.md

@@ -93,7 +93,8 @@ This runs lint, format checks, compile checks, tests, and package build.
   - `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/error/parsing manager+tool module enforcement of shared plain-type helper usage),
   - `tests/test_contributing_architecture_guard_listing.py` (`CONTRIBUTING.md` architecture-guard inventory completeness enforcement),
-  - `tests/test_examples_syntax.py` (example script syntax guardrail).
+  - `tests/test_examples_syntax.py` (example script syntax guardrail),
+  - `tests/test_docs_python3_commands.py` (`README`/`CONTRIBUTING`/examples python3 command consistency enforcement).
 
 ## Code quality conventions
 

tests/test_architecture_marker_usage.py

@@ -23,6 +23,7 @@
     "tests/test_core_type_helper_usage.py",
     "tests/test_contributing_architecture_guard_listing.py",
     "tests/test_examples_syntax.py",
+    "tests/test_docs_python3_commands.py",
 )
 
 

tests/test_docs_python3_commands.py

@@ -0,0 +1,22 @@
+import re
+from pathlib import Path
+
+import pytest
+
+pytestmark = pytest.mark.architecture
+
+
+def test_readme_and_contributing_use_python3_commands():
+    readme_text = Path("README.md").read_text(encoding="utf-8")
+    contributing_text = Path("CONTRIBUTING.md").read_text(encoding="utf-8")
+
+    assert "python -m" not in readme_text
+    assert "python -m" not in contributing_text
+
+
+def test_example_run_blocks_use_python3():
+    legacy_python_pattern = re.compile(r"^\s*python\s+examples/.*$", re.MULTILINE)
+
+    for example_path in sorted(Path("examples").glob("*.py")):
+        example_text = example_path.read_text(encoding="utf-8")
+        assert not legacy_python_pattern.search(example_text)