00c3872882
The workflow owns its triggers and ci.yml does not call it. A reusable-workflow call holds the caller run in progress for the full build, and GitHub refuses `gh run rerun` on a run that is still in progress. A separate run reruns and cancels on its own. The job restores /nix/store from the GitHub Actions cache and saves from main only. A cache that a PR writes is visible to that PR alone, so a save there spends the quota of the repository and helps no later run.