fix(websocket): add 30s server-side heartbeat to prevent proxy idle disconnects (#770)

The WebSocket gateway never sent ping frames, so any reverse proxy with
an idle timeout (Cloudflare Tunnel ~100s, AWS ALB 60s, nginx 60s, etc.)
would silently tear down /shell, /ws and /plugin-ws/* connections after
the idle window. The UI reconnects automatically but users see a
"Connecting to shell" toast every 1–3 minutes during normal use and any
in-flight PTY/chat traffic can race the reconnect.

Schedule a 30s ws.ping() per connection at the gateway level, cleared on
close/error. ping/pong counts as protocol activity for all proxies that
implement WebSocket correctly, so this single change covers every
deployment topology without per-proxy tuning.

Fixes #769

Co-authored-by: Haile <118998054+blackmammoth@users.noreply.github.com>

server/modules/websocket/services/websocket-server.service.ts

@@ -31,6 +31,24 @@ export function createWebSocketServer(
   });
 
   wss.on('connection', (ws, request) => {
+    // Keep WebSocket alive across reverse-proxy idle timeouts (Cloudflare ~100s,
+    // AWS ALB 60s, nginx 60s, etc.). Without app-level pings these connections
+    // are silently torn down even when the UI is active, causing repeated
+    // reconnect cycles. ws library heartbeat is opt-in.
+    const HEARTBEAT_INTERVAL_MS = 30_000;
+    const heartbeat = setInterval(() => {
+      if (ws.readyState === ws.OPEN) {
+        try {
+          ws.ping();
+        } catch {
+          // socket may have been closed concurrently — interval will be cleared below
+        }
+      }
+    }, HEARTBEAT_INTERVAL_MS);
+    const stopHeartbeat = () => clearInterval(heartbeat);
+    ws.on('close', stopHeartbeat);
+    ws.on('error', stopHeartbeat);
+
     const incomingRequest = request as AuthenticatedWebSocketRequest;
     const url = incomingRequest.url ?? '/';
     const pathname = new URL(url, 'http://localhost').pathname;