ci(release): delete preview releases after the deliverable publishes (#6729)

Preview tags stay as the traceability record for the validated commit, but their GitHub Releases are internal validation state and should not accumulate on the Releases page next to real deliverables.

Add a cleanup-preview-releases job that runs after publish-release succeeds for a release or prerelease tag and deletes every Release whose tag is exactly <target>-preview.<digits>. The tags themselves are kept: the job never passes --cleanup-tag. Tag matching uses jq string operations rather than a regex over the version, so dots in the version cannot widen the match, and the release listing is fetched before filtering so an API failure aborts the job instead of looking like there was nothing to clean up.

Extend the preview release workflow guard with the job condition, the delete invocation, both tag-matching filters, and an absent check for --cleanup-tag.

.github/workflows/build.yml

@@ -1033,6 +1033,55 @@ jobs:
           echo "🎉 Released $TAG successfully!"
           echo "📄 Release URL: ${{ needs.create-release.outputs.release_url }}"
 
+  # Remove the internal preview releases once the deliverable release is live.
+  # Only the Releases are deleted; the -preview.N tags stay so the validated
+  # commit remains traceable.
+  cleanup-preview-releases:
+    name: Cleanup Preview Releases
+    needs: [ build-check, publish-release ]
+    if: startsWith(github.ref, 'refs/tags/') && (needs.build-check.outputs.build_type == 'release' || needs.build-check.outputs.build_type == 'prerelease')
+    runs-on: ubuntu-latest
+    timeout-minutes: 30
+    permissions:
+      contents: write
+    steps:
+      - name: Delete preview releases for this target
+        env:
+          GH_TOKEN: ${{ github.token }}
+        shell: bash
+        run: |
+          set -euo pipefail
+
+          TAG="${{ needs.build-check.outputs.version }}"
+          RELEASES_JSON="${RUNNER_TEMP}/releases.json"
+
+          # Fetch before filtering: a failed listing must abort here instead of
+          # looking like "nothing to clean up".
+          gh api --paginate "repos/${GITHUB_REPOSITORY}/releases?per_page=100" > "$RELEASES_JSON"
+
+          # Match only <target>-preview.<digits>. String operations, not a
+          # regex over the tag, so dots in the version cannot widen the match.
+          DELETED=0
+          while IFS= read -r preview_tag; do
+            [[ -n "$preview_tag" ]] || continue
+            echo "🧹 Deleting preview release $preview_tag (tag kept)"
+            gh release delete "$preview_tag" --yes
+            DELETED=$((DELETED + 1))
+          done < <(
+            jq -r --arg tag "$TAG" '
+              .[]
+              | select(.tag_name | startswith($tag + "-preview."))
+              | select(.tag_name | ltrimstr($tag + "-preview.") | test("^[0-9]+$"))
+              | .tag_name
+            ' "$RELEASES_JSON"
+          )
+
+          if [[ "$DELETED" -eq 0 ]]; then
+            echo "ℹ️  No preview releases to clean up for $TAG"
+          else
+            echo "✅ Removed $DELETED preview release(s) for $TAG"
+          fi
+
   alert-on-failure:
     name: Alert on scheduled failure
     needs: [build-check, prepare-platform-matrix, build-rustfs, build-summary]