fix: harden telemetry parsing and null node fallbacks

CHANGELOG.md

@@ -41,6 +41,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - **(Planned)** Port 2375 (TCP) fallback support; future releases may require SSH-only for Node config.
 
 ### Fixed
+- Fixed backend MonitorService crash (`Cannot read properties of undefined (reading 'cpu_usage')`) occurring when Docker containers lacked CPU telemetry during transition states.
+- Handled UI deleted nodes ghost API calls by intercepting 404 errors globally in API and forcing the UI to resync to the default Node context.
+- Hardened `nodeContextMiddleware` in Express to intercept queries to invalid or deleted Node IDs gracefully instead of bubbling to Docker API 500 crashes.
+- Hardened Remote Node connection testing (`docker.info()`) to explicitly validate expected Docker API daemon properties instead of merely checking string length.
+- Caught Unhandled SFTP Promise Rejections in Node registry gracefully returning empty arrays to prevent frontend loading UI stalls.
+- Fixed horizontal UI overflowing in Node Manager settings on smaller resolutions.
 - **Fixed:** Docker API parsing bug where HTML string responses from misconfigured ports were counted as containers.
 - **Fixed:** Stack list crashing when SFTP connections fail by gracefully catching SSH errors and returning empty arrays.
 

backend/src/index.ts

@@ -67,6 +67,16 @@ const nodeContextMiddleware = (req: Request, res: Response, next: NextFunction)
   } else {
     req.nodeId = NodeRegistry.getInstance().getDefaultNodeId();
   }
+
+  // Intercept requests to deleted nodes to prevent downstream errors
+  if (req.path.startsWith('/api/') && !req.path.startsWith('/api/auth/')) {
+    const node = DatabaseService.getInstance().getNode(req.nodeId);
+    if (!node) {
+      res.status(404).json({ error: `Node with id ${req.nodeId} not found or was deleted.` });
+      return;
+    }
+  }
+
   next();
 };
 

backend/src/services/MonitorService.ts

@@ -311,8 +311,10 @@ export class MonitorService {
 
     private calculateCpuPercent(stats: any): number {
         let cpuPercent = 0.0;
+        if (!stats?.cpu_stats?.cpu_usage || !stats?.precpu_stats?.cpu_usage) return 0.0;
+
         const cpuDelta = stats.cpu_stats.cpu_usage.total_usage - stats.precpu_stats.cpu_usage.total_usage;
-        const systemDelta = stats.cpu_stats.system_cpu_usage - stats.precpu_stats.system_cpu_usage;
+        const systemDelta = (stats.cpu_stats.system_cpu_usage || 0) - (stats.precpu_stats.system_cpu_usage || 0);
         const numCpus = stats.cpu_stats.online_cpus || (stats.cpu_stats.cpu_usage.percpu_usage ? stats.cpu_stats.cpu_usage.percpu_usage.length : 1);
 
         if (systemDelta > 0.0 && cpuDelta > 0.0) {
@@ -322,6 +324,8 @@ export class MonitorService {
     }
 
     private calculateMemoryPercent(stats: any): number {
+        if (!stats?.memory_stats?.usage || !stats?.memory_stats?.limit) return 0.0;
+        
         const used_memory = stats.memory_stats.usage - (stats.memory_stats.stats?.cache || 0);
         const available_memory = stats.memory_stats.limit;
         if (available_memory > 0) {

frontend/src/context/NodeContext.tsx

@@ -48,6 +48,16 @@ export function NodeProvider({ children }: { children: React.ReactNode }) {
           const updatedActive = data.find((n: Node) => n.id === activeNode.id);
           if (updatedActive) {
             setActiveNodeState(updatedActive);
+          } else {
+            // The active node was deleted! Fallback to default
+            const defaultNode = data.find((n: Node) => n.is_default);
+            if (defaultNode) {
+              setActiveNodeState(defaultNode);
+            } else if (data.length > 0) {
+              setActiveNodeState(data[0]);
+            } else {
+              setActiveNodeState(null);
+            }
           }
         }
       }
@@ -65,7 +75,15 @@ export function NodeProvider({ children }: { children: React.ReactNode }) {
 
   useEffect(() => {
     refreshNodes();
-  }, []);
+
+    const handleNodeNotFound = () => {
+      console.warn('[NodeContext] Active node is unreachable or deleted. Forcing sync...');
+      refreshNodes();
+    };
+
+    window.addEventListener('node-not-found', handleNodeNotFound);
+    return () => window.removeEventListener('node-not-found', handleNodeNotFound);
+  }, [refreshNodes]);
 
   return (
     <NodeContext.Provider value={{ nodes, activeNode, setActiveNode, refreshNodes, isLoading }}>

frontend/src/lib/api.ts

@@ -24,6 +24,19 @@ export async function apiFetch(
     throw new Error('Unauthorized');
   }
 
+  // Intercept 404 Node Not Found responses and force context refresh
+  if (response.status === 404) {
+    try {
+      const clone = response.clone();
+      const errData = await clone.json();
+      if (errData.error && errData.error.includes('not found') && errData.error.includes('Node')) {
+        window.dispatchEvent(new Event('node-not-found'));
+      }
+    } catch (e) {
+      // Ignore JSON parse errors, caller handles standard 404s
+    }
+  }
+
   return response;
 }