Cost-control and bootstrap hardening
- Reuses one shared Hetzner pool host for 45 minutes, reducing minimum-hour lifecycle churn between nearby releases.
- Keeps the hard one-host-per-pool invariant with at most two isolated disposable runner/DinD pairs.
- Uses a short-lived public-only bootstrap SSH-key object so Hetzner does not generate or email a root password for scale-to-zero hosts.
- Retains resources across ambiguous provider outcomes and cleans the bootstrap key only after provider-observed server-create completion.
- Extends inventory and orphan cleanup coverage to pool SSH-key objects.
Verified live on Cloudflare Worker revision b6bc7ddd-be96-4e9a-8823-9259bc09fa6d: AtlasRepo Scout run 33022130760 succeeded on runner jit-98354819072; independent peak inventory showed exactly one pool server and zero legacy resources; the runner record was removed after completion; no Hetzner password email was generated.