Fix stale alerts for deleted agents on command deck

server/internal/alerts/evaluator.go

@@ -194,6 +194,30 @@ func (e *Evaluator) ActiveAlerts() []AlertEvent {
 	return out
 }
 
+// ClearAgent removes all in-memory alert state for a specific agent.
+// Call this when an agent is deleted so stale alerts stop appearing on the
+// dashboard for machines that no longer exist.
+func (e *Evaluator) ClearAgent(agentID string) {
+	e.mu.Lock()
+	defer e.mu.Unlock()
+	// Remove cached alerts for this agent.
+	filtered := e.activeAlerts[:0]
+	for _, a := range e.activeAlerts {
+		if a.AgentID != agentID {
+			filtered = append(filtered, a)
+		}
+	}
+	e.activeAlerts = filtered
+	// Remove cooldown + baseline entries so the agent's next appearance
+	// (e.g. re-registration) starts fresh.
+	delete(e.baseline, agentID)
+	for k := range e.lastFired {
+		if len(k) > len(agentID) && k[len(k)-len(agentID):] == agentID {
+			delete(e.lastFired, k)
+		}
+	}
+}
+
 func formatPct(v float64) string {
 	if v < 0 {
 		v = 0

server/internal/api/fleet_handler.go

@@ -522,6 +522,11 @@ func (f *FleetHandler) DeleteAgent(w http.ResponseWriter, r *http.Request) {
 		http.Error(w, "delete failed: "+err.Error(), http.StatusInternalServerError)
 		return
 	}
+	// Clear stale in-memory alerts so the machine stops showing up in the
+	// dashboard alert banner after deletion.
+	if f.alerts != nil {
+		f.alerts.ClearAgent(id)
+	}
 	w.Header().Set("Content-Type", "application/json")
 	json.NewEncoder(w).Encode(map[string]bool{"success": true})
 }
@@ -543,6 +548,9 @@ func (f *FleetHandler) BulkDeleteAgents(w http.ResponseWriter, r *http.Request)
 		}
 		if err := f.db.DeleteAgent(id); err == nil {
 			deleted++
+			if f.alerts != nil {
+				f.alerts.ClearAgent(id)
+			}
 		}
 	}
 	w.Header().Set("Content-Type", "application/json")

server/web/src/context/WebSocketProvider.tsx

@@ -108,6 +108,9 @@ export function WebSocketProvider({ children }: { children: React.ReactNode }) {
           case 'agent_deleted': {
             const { agent_id } = msg.payload as { agent_id: string };
             setAgents((prev) => prev.filter((a) => a.id !== agent_id));
+            // Also purge any cached alerts for this agent so the dashboard
+            // alert banner stops showing errors for machines that no longer exist.
+            setFleetAlerts((prev) => prev.filter((a) => a.agent_id !== agent_id));
             break;
           }
           case 'stats_update': {