Improve stale PR auto-labeling and management

Enhance stale PR management by auto-labeling PRs with no activity in the last 14 days and maintaining existing stale PR handling.

.github/workflows/stale_pr_close.yml

@@ -38,7 +38,7 @@ jobs:
               return;
             }
 
-            // --- Scheduled run: check all stale PRs ---
+            // --- Scheduled run: fetch all open PRs ---
             const { data: prs } = await github.rest.pulls.list({
               owner,
               repo,
@@ -47,8 +47,63 @@ jobs:
             });
 
             for (const pr of prs) {
-              const hasStale = pr.labels.some(l => l.name === "stale");
+              const labels = pr.labels.map(l => l.name);
-              if (!hasStale) continue;
+              const hasStale = labels.includes("stale");
+              const hasKeepOpen = labels.includes("keep-open");
+
+              // -------------------------------------------------------
+              // NEW: Auto-label PRs with no activity in the last 14 days
+              // -------------------------------------------------------
+              if (!hasStale && !hasKeepOpen) {
+                // Find the most recent commit date
+                const { data: commits } = await github.rest.pulls.listCommits({
+                  owner,
+                  repo,
+                  pull_number: pr.number
+                });
+                const lastCommitDate = commits.length > 0
+                  ? new Date(commits[commits.length - 1].commit.author.date)
+                  : new Date(pr.created_at);
+
+                // Find the most recent non-bot comment date
+                const { data: comments } = await github.rest.issues.listComments({
+                  owner,
+                  repo,
+                  issue_number: pr.number,
+                  per_page: 100
+                });
+                const humanComments = comments.filter(c => c.user?.type !== "Bot");
+                const lastCommentDate = humanComments.length > 0
+                  ? new Date(humanComments[humanComments.length - 1].created_at)
+                  : null;
+
+                // Most recent activity across commits and comments
+                const lastActivityDate = lastCommentDate && lastCommentDate > lastCommitDate
+                  ? lastCommentDate
+                  : lastCommitDate;
+
+                const daysSinceActivity = (now - lastActivityDate) / (1000 * 60 * 60 * 24);
+
+                if (daysSinceActivity > 14) {
+                  await github.rest.issues.addLabels({
+                    owner,
+                    repo,
+                    issue_number: pr.number,
+                    labels: ["stale"]
+                  });
+                  // The pull_request_target labeled event will fire the comment automatically.
+                  // Skip further processing for this PR in this run.
+                  continue;
+                }
+
+                // Not stale, nothing else to do for this PR.
+                continue;
+              }
+
+              // -------------------------------------------------------
+              // EXISTING: Manage already-stale PRs
+              // -------------------------------------------------------
+              if (!hasStale) continue; // has keep-open but not stale — skip
 
               // Get timeline events to find when stale label was added
               const { data: events } = await github.rest.issues.listEvents({