The zsh login-shell legs in remote-lifecycle.test.ts and
ssh-connection.test.ts silently returned when zsh was missing, and the
js-tests runner image ships no zsh, so the #111949 coverage never ran on
CI and a wrapper regression stayed green.
- js-tests.yml: install zsh on the Linux runner before the checks.
- Both legs now report vitest skips ('zsh not installed') instead of
passing; the ssh-connection leg is its own test so the skip is visible.
- Docs: note the zsh degraded mode (no process-group kill for a hung
probe's grandchildren) in the SSH connection guide.
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