fix: keep terminal sessions alive

Add WebSocket and SSH keepalives so idle dashboard terminal sessions stay connected across proxies and long-running idle periods.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

dashboard/backend/routers/terminal.py

@@ -72,6 +72,8 @@ async def ws_endpoint(websocket: WebSocket, host: str = Query("nas")):
         conn = await asyncssh.connect(
             h["host"], username=h["user"],
             client_keys=[h["key"]], known_hosts=_known_hosts,
+            keepalive_interval=30,
+            keepalive_count_max=3,
         )
     except Exception:
         _active_sessions.discard(session_id)
@@ -108,6 +110,8 @@ async def ws_endpoint(websocket: WebSocket, host: str = Query("nas")):
                     else:
                         process.stdin.write(data)
                 elif "text" in msg and msg["text"]:
+                    if msg["text"] == "__ping__":
+                        continue
                     process.stdin.write(msg["text"].encode())
         except WebSocketDisconnect:
             pass

dashboard/frontend/src/routes/Terminal.svelte

@@ -122,6 +122,7 @@
     if (d) {
       d.voice?.destroy();
       d.ro?.disconnect();
+      if (d.heartbeat) clearInterval(d.heartbeat);
       d.term?.element?.removeEventListener("dragover", d.handleDragOver);
       d.term?.element?.removeEventListener("drop", d.handleDrop);
       d.term?.textarea?.removeEventListener("paste", d.handlePaste);
@@ -180,6 +181,10 @@
       ws.onerror = () => updateTab(tabId, { connected: false, error: "Connection failed" });
       term.onData((data) => ws.readyState === 1 && ws.send(new TextEncoder().encode(data)));
 
+      const heartbeat = setInterval(() => {
+        if (ws.readyState === 1) ws.send("__ping__");
+      }, 25000);
+
       const handleDragOver = (e) => {
         e.preventDefault();
       };
@@ -211,7 +216,7 @@
       ro.observe(el);
       const voice = new VoiceSession(() => { voiceTick++; });
       voice.attach(term, ws);
-      tabData.set(tabId, { ws, term, ro, el, voice, handleDragOver, handleDrop, handlePaste });
+      tabData.set(tabId, { ws, term, ro, el, voice, heartbeat, handleDragOver, handleDrop, handlePaste });
     })();
   }
 
@@ -222,6 +227,7 @@
     tabData.forEach((d) => {
       d.voice?.destroy();
       d.ro?.disconnect();
+      if (d.heartbeat) clearInterval(d.heartbeat);
       d.term?.element?.removeEventListener("dragover", d.handleDragOver);
       d.term?.element?.removeEventListener("drop", d.handleDrop);
       d.term?.textarea?.removeEventListener("paste", d.handlePaste);