Yes you're right! There was something wrong with poetry build system. When I initialised the poetry project roughly a year ago it placed an unpinned dependency (for the build part) for cryptography which recently switched to rust. I'm not sure why poetry hadn't vendorized that package or, at least, pinned the version. In any case, I updated the repo's pyproject.toml to use poetry's new build settings. Then, to check the install works in docker I switched to python's base images and did the following:

  docker run -it --rm python:latest /bin/bash
  curl -sSL https://raw.githubusercontent.com/python-poetry/poetry/master/get-poetry.py | python -
  cd /tmp
  git clone https://github.com/bsdz/calcengine.git
  cd calcengine
  python3 -mvenv --prompt calceng .venv
  . ./.venv/bin/activate
  pip install "cppy>=1.1.0"
  ~/.poetry/bin/poetry install -E demo

Note that I had to force cppy to install using pip. At some point I'll refresh the poetry lock file to fix these glitches that seem to appear as an untouched project ages.