Dockerfile.ci adds zsh so the sourced-helper guard runs (and fails loudly
when zsh is missing) inside the eval container too. The macOS named
regressions job sources bin/gstack-codex-probe from zsh in an unrelated
directory and runs _gstack_codex_select_model exec (no paid call), then runs
the sourced-helper guard on the macOS runner. A free test pins both lanes and
runs the macOS step's script locally.
garrytan
fa79a3071e