feat(cluster): add GET /:id/ping to probe node agent reachability and latency

services/mam-api/src/routes/cluster.js

@@ -66,6 +66,32 @@ router.post('/heartbeat', async (req, res, next) => {
   } catch (err) { next(err); }
 });
 
+// GET /:id/ping – probe the node's api_url/health endpoint directly
+router.get('/:id/ping', async (req, res, next) => {
+  try {
+    const r = await pool.query(
+      'SELECT id, hostname, api_url FROM cluster_nodes WHERE id = $1',
+      [req.params.id]
+    );
+    if (r.rowCount === 0) return res.status(404).json({ error: 'Node not found' });
+
+    const node = r.rows[0];
+    if (!node.api_url) return res.json({ reachable: false, reason: 'no api_url registered' });
+
+    const start = Date.now();
+    try {
+      const upstream = await fetch(`${node.api_url}/health`, {
+        signal: AbortSignal.timeout(4000),
+      });
+      const latency_ms = Date.now() - start;
+      const body = await upstream.json().catch(() => ({}));
+      res.json({ reachable: upstream.ok, latency_ms, status: upstream.status, agent: body });
+    } catch (err) {
+      res.json({ reachable: false, latency_ms: Date.now() - start, reason: err.message });
+    }
+  } catch (err) { next(err); }
+});
+
 // DELETE /:id – deregister a node
 router.delete('/:id', async (req, res, next) => {
   try {
@@ -73,7 +99,7 @@ router.delete('/:id', async (req, res, next) => {
       'DELETE FROM cluster_nodes WHERE id = $1 RETURNING id',
       [req.params.id]
     );
-    if (r.rowCount === 0) return res.status(404).json({ error: 'Node not found' });
+    if (r.rowCount === 0) return res.status(404).json({ error: 'Node not found' });;
     res.json({ ok: true });
   } catch (err) { next(err); }
 });