[edsonsims]

An explicit env_files = [] in native TOML still loads INI-style fallback files. For example, a pytest.toml with [pytest] env_files = ["fallback.env"] and [pytest_env] env_files = [] imports the variables from fallback.env. The same happens when extending configuration with --envfile +cli.env.

Keep absent native env_files as None, so omission preserves the INI fallback while an explicit empty list suppresses it. CLI files still load. Add subprocess regressions for pytest.toml, .pytest.toml, and adjacent pyproject.toml/pytest.ini, covering both omission and explicit emptiness with and without CLI extension.

Validation on macOS, Python 3.13.1 and pytest 9.1.1:

• Before the fix: the new regression matrix had 6 failures and 6 passes.
• After the fix: all 12 regression cases pass; full suite: 103 passed.
• Coverage: 100% statements/branches under the repository configuration.
• Ruff check, Ruff format check, and git diff --check pass.

AI assistance: OpenAI Codex drafted the change and performed automated review and the local checks above. No claim of owner manual review is made. Maintainer review is requested.