Use when the user wants to promote a release from one env-Space to the next, or push a base revision to every downstream across the fleet — phrases like "promote to staging", "roll forward to prod", "push this release to the next environment", "upgrade the downstream Units to match upstream", "is staging ready to roll forward?", "what do I need to check before promoting to prod?", "preflight before pushing the release to prod", "which Units are behind their upstream?". One skill for the whole promotion arc: runs the preflight checks (source converged, destination in scope, diffs sane, policy + approval ready, upstream linkage matches intent) to produce a go / no-go and a concrete scope; on go, wraps the promotion in a ChangeSet, bulk-runs `cub unit update --patch --upgrade --where ...`, closes the ChangeSet, and hands off to `cub-apply` for the rollout. Do not load for rollback of a prior promotion (use `rollback-revision` + `references/changesets.md`), cluster-ConfigHub drift (use `drift-reconcile`), post-promotion verification (use `verify-apply`), or single-Unit in-place mutations (use `cub-mutate`).