ISSUE-003: Add failing test for fail-fast on frame access

Add pytest `test_fail_fast_when_frame_access_fails` that monkeypatches
`sys._getframe` to raise during `PY_START`. It asserts the runtime tracer
propagates a Python exception instead of silently swallowing the failure.

This currently fails due to the defensive fallback in `on_py_start`.

Author: tzanko-matev

codetracer-python-recorder/tests/test_fail_fast_on_py_start.py

@@ -0,0 +1,44 @@
+import runpy
+import sys
+from pathlib import Path
+
+import pytest
+
+
+def test_fail_fast_when_frame_access_fails(tmp_path: Path):
+    # Import the built extension module
+    import codetracer_python_recorder as cpr
+
+    # Prepare a simple program that triggers a Python function call
+    prog = tmp_path / "prog.py"
+    prog.write_text(
+        """
+def f():
+    return 1
+
+f()
+"""
+    )
+
+    # Monkeypatch sys._getframe to simulate a failure when capturing args
+    original_getframe = getattr(sys, "_getframe")
+
+    def boom(*_args, **_kwargs):  # pragma: no cover - intentionally fails
+        raise RuntimeError("boom: _getframe disabled")
+
+    sys._getframe = boom  # type: ignore[attr-defined]
+
+    try:
+        # Start tracing; activate only for our program path so stray imports don't trigger
+        cpr.start_tracing(str(tmp_path), "json", activation_path=str(prog))
+
+        with pytest.raises(RuntimeError) as excinfo:
+            runpy.run_path(str(prog), run_name="__main__")
+
+        # Ensure the error surfaced clearly and didn’t get swallowed
+        assert "_getframe" in str(excinfo.value) or "boom" in str(excinfo.value)
+    finally:
+        # Restore state
+        sys._getframe = original_getframe  # type: ignore[attr-defined]
+        cpr.stop_tracing()
+