Remote stack logs: surface proxy/agent errors instead of silent disconnect (0.13.1)

Remote-stack log streaming showed only "disconnected, 0 lines" whenever the
agent log proxy failed, because the LogViewer ignored type:"error" messages and
the proxy swallowed connection errors.

- ws.py: the agent-logs proxy now reports a clear, logged reason on failure —
  distinguishes "cannot reach agent <url>" from a handshake rejection (HTTP 404
  hints the agent is outdated and lacks live-log support) and forwards abnormal
  upstream close codes (e.g. 4401 bad agent token).
- LogViewer: renders type:"error" messages (red) and surfaces a 4401 close as an
  authorization error, instead of silently showing "Waiting for log output…".

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/agent_app.py

@@ -40,7 +40,7 @@ from services import backup_service, compose_service
 
 logger = logging.getLogger("stackpilot.agent")
 
-AGENT_VERSION = "0.13.0"
+AGENT_VERSION = "0.13.1"
 
 
 # --------------------------------------------------------------------------- #

backend/main.py

@@ -55,7 +55,7 @@ async def lifespan(app: FastAPI):
     schedule_task.cancel()
 
 
-app = FastAPI(title="StackPilot", version="0.13.0", lifespan=lifespan)
+app = FastAPI(title="StackPilot", version="0.13.1", lifespan=lifespan)
 
 app.add_middleware(
     CORSMiddleware,

backend/routers/ws.py

@@ -3,6 +3,7 @@ from __future__ import annotations
 
 import asyncio
 import json
+import logging
 
 import contextlib
 
@@ -16,6 +17,8 @@ from database import engine
 from models.agent import Agent
 from services import compose_service
 
+logger = logging.getLogger("stackpilot.ws")
+
 router = APIRouter(tags=["ws"])
 
 
@@ -113,18 +116,47 @@ async def ws_agent_logs(
               else "ws://" + base)
     ws_url += f"/agent/ws/logs/{stack_id}?token={agent.token}"
 
+    async def _err(detail: str) -> None:
+        with contextlib.suppress(Exception):
+            await websocket.send_text(json.dumps({"type": "error", "detail": detail}))
+
+    # Connect to the agent. Surface connection problems (agent down, wrong URL,
+    # an outdated agent that lacks /agent/ws/logs, TLS issues) instead of
+    # silently dropping the socket.
+    try:
+        upstream = await websockets.connect(ws_url, open_timeout=10, ping_interval=20)
+    except websockets.InvalidStatus as exc:
+        code = getattr(getattr(exc, "response", None), "status_code", None)
+        hint = " — the agent may be running an old version without live-log support; update it." if code == 404 else ""
+        logger.warning("Agent log proxy: handshake to %s failed (%s)", agent.name, code)
+        await _err(f"Agent '{agent.name}' rejected the log stream (HTTP {code}){hint}")
+        with contextlib.suppress(Exception):
+            await websocket.close()
+        return
+    except Exception as exc:  # noqa: BLE001
+        logger.warning("Agent log proxy: cannot reach %s at %s: %s", agent.name, agent.url, exc)
+        await _err(f"Could not connect to agent '{agent.name}' at {agent.url}: {exc}")
+        with contextlib.suppress(Exception):
+            await websocket.close()
+        return
+
     try:
-        async with websockets.connect(ws_url, open_timeout=10, ping_interval=20) as upstream:
         async for message in upstream:
             await websocket.send_text(
                 message if isinstance(message, str) else message.decode("utf-8", "replace")
             )
     except WebSocketDisconnect:
         pass
+    except websockets.ConnectionClosed as exc:
+        # Abnormal upstream close (e.g. 4401 bad token, or agent-side error).
+        if exc.code not in (1000, 1001):
+            await _err(f"Agent log stream closed unexpectedly (code {exc.code}).")
     except Exception as exc:  # noqa: BLE001
-        with contextlib.suppress(Exception):
+        logger.warning("Agent log proxy: stream error from %s: %s", agent.name, exc)
-            await websocket.send_text(json.dumps({"type": "error", "detail": str(exc)}))
+        await _err(str(exc))
     finally:
+        with contextlib.suppress(Exception):
+            await upstream.close()
         with contextlib.suppress(Exception):
             await websocket.close()
 

frontend/package.json

@@ -1,7 +1,7 @@
 {
   "name": "stackpilot-frontend",
   "private": true,
-  "version": "0.13.0",
+  "version": "0.13.1",
   "type": "module",
   "scripts": {
     "dev": "vite",

frontend/src/components/stacks/LogViewer.tsx

@@ -25,11 +25,14 @@ export function LogViewer({ stackId, agentId }: { stackId: string; agentId?: num
   const [lines, setLines] = useState<{ service: string | null; line: string }[]>([]);
   const [autoScroll, setAutoScroll] = useState(true);
   const [connected, setConnected] = useState(false);
+  const [error, setError] = useState<string | null>(null);
   const containerRef = useRef<HTMLDivElement>(null);
   const token = useAuthStore((s) => s.accessToken);
 
   useEffect(() => {
     if (!token) return;
+    setError(null);
+    let gotError = false;
     const proto = window.location.protocol === "https:" ? "wss" : "ws";
     const path =
       agentId != null
@@ -38,7 +41,13 @@ export function LogViewer({ stackId, agentId }: { stackId: string; agentId?: num
     const url = `${proto}://${window.location.host}${path}?token=${token}`;
     const ws = new WebSocket(url);
     ws.onopen = () => setConnected(true);
-    ws.onclose = () => setConnected(false);
+    ws.onclose = (ev) => {
+      setConnected(false);
+      // Auth rejection from the proxy/agent (JWT or agent token) closes 4401.
+      if (!gotError && ev.code === 4401) {
+        setError("Not authorized to stream logs (session or agent token).");
+      }
+    };
     ws.onmessage = (ev) => {
       try {
         const msg = JSON.parse(ev.data);
@@ -47,6 +56,9 @@ export function LogViewer({ stackId, agentId }: { stackId: string; agentId?: num
             const next = [...prev, { service: msg.service, line: msg.line }];
             return next.length > MAX_LINES ? next.slice(-MAX_LINES) : next;
           });
+        } else if (msg.type === "error") {
+          gotError = true;
+          setError(msg.detail || "Log stream error");
         }
       } catch {
         /* ignore */
@@ -96,7 +108,12 @@ export function LogViewer({ stackId, agentId }: { stackId: string; agentId?: num
         ref={containerRef}
         className="flex-1 overflow-auto rounded-lg bg-slate-950 p-3 font-mono text-xs leading-relaxed"
       >
-        {lines.length === 0 && (
+        {error && (
+          <div className="mb-1 whitespace-pre-wrap break-words text-rose-400">
+            ⚠ {error}
+          </div>
+        )}
+        {lines.length === 0 && !error && (
           <div className="text-slate-500">Waiting for log output…</div>
         )}
         {lines.map((l, i) => (