diff --git a/conftest.py b/conftest.py
new file mode 100644
index 0000000..97da40f
--- /dev/null
+++ b/conftest.py
@@ -0,0 +1,17 @@
+"""Root conftest — ensures the project root is on sys.path.
+
+Required when the virtual-environment Python is symlinked to an external
+interpreter (e.g. Anaconda) that does not process the venv's .pth files
+automatically.  Adding the project root here makes ``codex`` importable
+regardless of how pytest is invoked (``pytest``, ``python -m pytest``, etc.).
+"""
+
+from __future__ import annotations
+
+import sys
+from pathlib import Path
+
+# Insert the project root so `import codex` always resolves.
+_project_root = str(Path(__file__).parent)
+if _project_root not in sys.path:
+    sys.path.insert(0, _project_root)