fix(recipe-upgrade): stop auto-closing superseded/unrelated open PRs

Per operator: opening a new upgrade PR should stack ON TOP of any other
still-open PRs, not close them. Only PRs already merged into upstream
main are closed (merging them is a no-op). This prevents the phase-7
incident where an unrelated open ghost PR was auto-closed as 'superseded'.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.claude/skills/recipe-upgrade/SKILL.md

@@ -76,9 +76,10 @@ ssh cc-ci "GITEA_USERNAME='$GITEA_USERNAME' GITEA_PASSWORD='$GITEA_PASSWORD' GIT
    < /srv/cc-ci/.claude/skills/recipe-upgrade/open-recipe-pr.sh
 ```
 This (a) re-syncs mirror `main` to true upstream main, (b) **closes any open PR already merged
-upstream**, (c) **closes any other still-open PR for this recipe as superseded**, then pushes the
-upgrade branch and opens the new PR **in its place** (so the diff is exactly this upgrade, against the
-real current upstream main). Capture the `PR_URL`. Optionally export `RECIPE_PR_BODY` first (image-tag
+upstream** (merging it would be a no-op), then pushes the upgrade branch and opens the new PR
+**alongside** any other still-open PRs — it does **NOT** close superseded/unrelated open PRs; the
+operator decides which to merge/close. The new PR's diff is still exactly this upgrade against the
+real current upstream main. Capture the `PR_URL`. Optionally export `RECIPE_PR_BODY` first (image-tag
 table + the planned operator-action notes). Re-running with the same target version updates the
 existing same-branch PR rather than duplicating it.
 
@@ -150,8 +151,8 @@ Always state explicitly that **nothing was merged** — the PR(s) await operator
   explanatory PR **comment**, never a test edit. Only `--with-tests` opens a cc-ci test PR. The weekly
   `/upgrade-all` cron always runs the **default** — it never auto-updates tests.
 - **Mirror reflects reality.** Each run force-syncs the `recipe-maintainers/<recipe>` mirror `main` to
-  true upstream main, closes open PRs already merged upstream, and replaces any superseded open PR with
-  the new one — so an open mirror PR always means "genuinely still open against current upstream main".
+  true upstream main and closes open PRs already merged upstream. It does NOT close superseded/unrelated
+  open PRs — a new upgrade PR is opened alongside them and the operator decides which to merge/close.
 - **Prefer a recipe-only PR.** Only open a cc-ci test PR (under `--with-tests`) when the upgrade is
   correct but a test is genuinely stale — never to paper over a real upgrade regression.
 - **Never weaken a test**; **bounded** changes (the upgrade + minimal test update, not rewrites).