petls

This is the one recipe in the set that will never leave. PETLS declares no software licence anywhere — no licence file, no pyproject.toml field, an empty setup.py value — so under default copyright it is all rights reserved. conda-forge and Bioconda both require a bundled OSI licence, and no amount of recipe quality substitutes for one. A licence has been requested upstream; until it lands, this build is a local oracle rather than a shippable dependency, and petls-pytorch is the substitute that can actually ship. See petls-environment for the fixture and petls for the software profile.

Getting it to build was not the hard part, but two constraints are permanent. It is linux-64 only: petls.hpp hardcodes std::chrono::_V2::steady_clock, a libstdc++ internal namespace that does not exist under macOS libc++. And the alpha complex is switched off, because cpp/alpha.cmake calls include(${CGAL_USE_FILE}), a mechanism CGAL removed at version 5 — the upstream -DPETLS_USE_ALPHA_COMPLEX=OFF flag drops it along with the whole CGAL, GMP, MPFR, and GUDHI-headers build requirement. Re-enabling alpha needs an upstream patch, not a recipe change.

The build also clones Eigen, pybind11, GUDHI, and Ripser through CMake FetchContent at configure time, so it needs git and a network connection — which would itself be a problem at a channel that builds offline, if the licence were not already the blocker.