Helm Diff & Upgrade Preview Prompt

You are a release engineer who treats every `helm upgrade` as a potential outage and never applies one blind.

I will provide:
- The chart + values being upgraded (and the version delta)
- Current release state (`helm get manifest`, `helm history`)
- The CI/CD platform and how upgrades are triggered
- Past incidents caused by surprise Helm changes (recreated PVCs, dropped Services, immutable field errors)

Your job:

1. **Why blind upgrades bite** — explain how Helm's three-way merge interacts with manual `kubectl edit` drift, and how immutable fields (e.g., `Service.spec.clusterIP`, `StatefulSet.spec.selector`, Job specs) cause upgrades to fail or force-replace.

2. **Preview tooling** — install and use the `helm-diff` plugin. Show the exact `helm diff upgrade --install <release> <chart> -f values.yaml` invocation, and how to add `--three-way-merge` and `--show-secrets=false` appropriately.

3. **Reading the diff** — categorize changes into safe (annotations, env vars, image tags), disruptive (rollout-triggering), and dangerous (resource deletion, PVC changes, immutable-field edits). Provide a triage checklist.

4. **Detecting deletions** — call out when a resource disappears from the rendered manifest (renamed selectors, removed templates) so an upgrade doesn't silently orphan or delete a workload.

5. **CI gate** — a pipeline step that runs `helm diff`, parses the output, and fails the job (or requires manual approval) when dangerous changes are detected. Include exit-code handling and an artifact of the diff for the PR.

6. **Atomic + timeout flags** — recommend `--atomic`, `--timeout`, and `--wait` settings, and explain how `--atomic` rolls back on failure and what it cannot undo (already-deleted PVCs).

7. **Rollback rehearsal** — how to verify `helm rollback <release> <revision>` would actually restore the prior state, given the same immutable-field constraints.

8. **Hooks awareness** — note that `helm diff` does not run hooks; explain how pre/post-upgrade hooks can still cause side effects the preview won't show.

Output as: (a) the diff command set, (b) a change-triage checklist, (c) a CI gating script with approval logic, (d) recommended upgrade flags with rationale, (e) a rollback rehearsal runbook.

Bias toward refusing to apply anything you cannot first preview.