Add stale issue triage dry run workflow

Add a conservative actions/stale workflow that reports backlog counts and runs in debug-only mode. Scope the temporary push trigger to the stale-issues branch and keep issue permissions read-only so the dry run cannot label, comment on, or close issues.

Author: mamoreau-devolutions

.github/workflows/stale.yml

@@ -0,0 +1,61 @@
+name: Stale Issue Triage
+
+on:
+  push:
+    branches: [ "stale-issues" ]
+    paths:
+      - '.github/workflows/stale.yml'
+  schedule:
+    - cron: '20 8 * * 1'
+  workflow_dispatch:
+
+permissions:
+  actions: read
+  issues: read
+  pull-requests: read
+
+jobs:
+  stale:
+    name: Stale issue dry run
+    runs-on: ubuntu-latest
+    steps:
+      - name: Backlog snapshot
+        env:
+          GH_TOKEN: ${{ github.token }}
+          REPOSITORY: ${{ github.repository }}
+        run: |
+          open_issues=$(gh api -X GET search/issues -f q="repo:$REPOSITORY is:issue is:open" --jq '.total_count')
+          unmilestoned_issues=$(gh api -X GET search/issues -f q="repo:$REPOSITORY is:issue is:open no:milestone" --jq '.total_count')
+          stale_issues=$(gh api -X GET search/issues -f q="repo:$REPOSITORY is:issue is:open label:stale" --jq '.total_count')
+          candidate_issues=$(gh api -X GET search/issues -f q="repo:$REPOSITORY is:issue is:open no:milestone -label:ready-to-go -label:needs-further-study -label:important -label:waiting-for-something -label:bug" --jq '.total_count')
+
+          {
+            echo '## Stale issue triage snapshot'
+            echo
+            echo '| Query | Count |'
+            echo '| --- | ---: |'
+            echo "| Open issues | $open_issues |"
+            echo "| Open unmilestoned issues | $unmilestoned_issues |"
+            echo "| Open issues already labeled stale | $stale_issues |"
+            echo "| Phase 1 dry-run candidates | $candidate_issues |"
+          } >> "$GITHUB_STEP_SUMMARY"
+
+      - name: Run stale issue dry run
+        uses: actions/stale@v10
+        with:
+          days-before-issue-stale: 365
+          days-before-issue-close: -1
+          days-before-pr-stale: -1
+          days-before-pr-close: -1
+          stale-issue-label: stale
+          stale-issue-message: >
+            This issue has not had recent activity. If it is still relevant,
+            please leave a comment with any updated context so we can keep it in
+            the active backlog. This initial rollout does not close issues
+            automatically.
+          exempt-all-issue-milestones: true
+          exempt-issue-labels: ready-to-go, needs-further-study, important, waiting-for-something, bug
+          remove-issue-stale-when-updated: true
+          operations-per-run: 1000
+          debug-only: true
+          enable-statistics: true