How to cache Poetry virtual environments in GitLab CI/CD?

I want to cache Poetry virtual environments between builds of my Python application. I have configured the pipeline so that the virtual environment is recreated every time pyproject.toml changes (poetry.lock is not comitted):

default: cache: - key: files: - lego/pyproject.toml paths: - lego/.venv - artifacts/build/layer/build/.venv - paths: - artifacts/pypoetry 

The virtual environment is created as follows:

poetry config virtualenvs.in-project true poetry install 

This works locally, but it fails in GitLab CI/CD on the second pipeline run:

$ LOG_LEVEL=ERROR poetry run pytest tests -n auto -v --cov=./src --junitxml=lego-report.xml ImportError while loading conftest '/builds/5565557/lddpro-bff/lego/tests/conftest.py'. tests/conftest.py:22: in <module> from lego.common.aws import S3, EventBridge, SSM, Secrets E ModuleNotFoundError: No module named 'lego' 

The reason is that pytest cannot locate the root package (lego). However, I have verified that the root package is located in the virtual environment (.venv):

$ cat .venv/lib/python*/site-packages/lego.pth /builds/5565557/lddpro-bff/lego/src 

Here lego.pth includes the current job ID in the path.

How can I properly cache Poetry virtual environments between CI/CD pipeline runs?

Job configuration:

lego: extends: .unittest variables: REPORT_NAME: lego-report.xml script: - cd lego - poetry config virtualenvs.in-project true && poetry install - poetry env info - env LOG_LEVEL=ERROR poetry run pytest tests -n auto -v --cov=./src --junitxml=${REPORT_NAME} - mv -f ${REPORT_NAME} ${CI_PROJECT_DIR}/ || echo "" - cd ${CI_PROJECT_DIR} - mkdir -p artifacts - cd tools - . ./build_deploy.sh --command=build --debug artifacts: paths: - artifacts/lego-function.zip - artifacts/lego-layer.zip reports: junit: ${REPORT_NAME} expire_in: 7 days rules: - if: $CI_COMMIT_BRANCH && $CI_PIPELINE_SOURCE != "merge_request_event" - if: $CI_PIPELINE_SOURCE == "merge_request_event"