Trying another way to resolve build-time dep.

install.sh

 #!/bin/sh
-/usr/bin/env python3 setup.py build_ext
+# /usr/bin/env python3 setup.py build_ext
 # .egg-link does not work with PYTHONPATH ?
 /usr/bin/env python3 -m pip install -e .
 /usr/bin/env python3 -m pip install --no-deps --ignore-installed .

pyproject.toml

+[build-system]
+requires = ["setuptools", "Cython"]
+build-backend = "setuptools.build_meta"

requirements.txt

-Cython
-cytoolz