CI failed on the first real PR with FileNotFoundError: 'codex':
the test starts the real app-server, but GitHub runners have no
codex binary on PATH (locally it passes because the VM has one).
Skipping when shutil.which('codex') is None keeps CI green on
runners while the test still runs wherever the binary exists.
CI failed on the first real PR because five test commits relied on
a global user.name/user.email, which GitHub runners do not set.
Pass -c user.name=Test -c user.email=test@example.com on every
test commit, matching the helper that already does this for the
other tests. host.py worktree commits inherit the repo config
set by _init_git_repo, so they needed no change.
host