Runner staging contract test

Run the shell-only shared staging regression from the repository root:

bash actions/test.runner-staging.sh

The action uses isolated temporary directories and mocked downloads. It checks local and published manifests, nested group-variable/playbook/runtime/ template paths, required manifest declarations, incomplete local checkouts without a published fallback, missing and empty dependencies, unsafe paths, duplicate entries, cleanup of partial downloads, and release-helper namespace isolation.

It does not access the network, call sudo, run Python or Ansible, install software, or modify generated publication files.