`run_approval_merge_config_pr` and `run_merge_config_pr` are gone; the
three phases are `run_deploy_merge_verify` (drift gate, fetch, verify —
mutates nothing), `run_deploy_apply` (merge + build) and
`run_deploy_tail` (compensation + push).
The rollback state is a git ref in the applied repo
(`refs/hyperhive/rollback/<approval-id>`) rather than a value handed
between nodes, because hive-c0re can restart between the apply and the
tail and the tail still has to know what to undo.
Rolling `main` back on a *successful* deploy is the worst thing the tail
can do, so it is guarded twice: the apply drops the rollback ref before
it plants `deployed/<id>`, and the tail refuses to compensate at all if
`deployed/<id>` resolves. It takes two independent git failures to get
there.
`run_deploy_tail` returns nothing and warns on every error — a failing
compensation must not mask the deploy's own verdict, which the terminal
hook takes from the DAG's roll-up.
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