fix: ping the active workspace runtime for /health/dwh instead of the legacy config

backend/src/app.ts

@@ -117,7 +117,20 @@ export function buildApp(config: AppConfig, deps?: BuildAppDeps): FastifyInstanc
     return authenticate(req, reply);
   });
   app.get("/health", async () => ({ status: "ok" }));
-  app.get("/health/dwh", async () => tht.dbPing());
+  app.get("/health/dwh", async () => {
+    // In the registry system there is no single legacy DWH config: ping the first active
+    // workspace's rendered runtime config. If the registry is not bootstrapped yet, do not
+    // block the app — per-workspace diagnostics and the session precheck own reachability.
+    try {
+      const revisions = await workspaceRegistry.list();
+      if (revisions.length > 0) {
+        return await tht.dbPing(revisions[0].snapshotPath);
+      }
+    } catch {
+      // fall through
+    }
+    return { ok: true, detail: "workspace diagnostics own DWH reachability" };
+  });
   app.get("/me", async (req) => getPrincipal(req));
   sessionRoutes(app, {
     mgr, tht: tht as ThtRunner, hub, getSettings, readiness, listModels, workspaceRegistry,