feat: include active alert count in MCP server instructions

Add InstructionsFunc callback to ServerConfig, called during each
initialize handshake to generate dynamic instructions. The lab-monitoring
server uses this to query Alertmanager and include a count of active
non-silenced alerts, so the LLM can proactively inform the user.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/monitoring/handlers.go

@@ -10,6 +10,50 @@ import (
 	"git.t-juice.club/torjus/labmcp/internal/mcp"
 )
 
+// AlertSummary queries Alertmanager for active (non-silenced) alerts and returns
+// a short summary string. Returns empty string if there are no alerts or if
+// Alertmanager is unreachable.
+func AlertSummary(am *AlertmanagerClient) string {
+	active := true
+	silenced := false
+	inhibited := false
+	alerts, err := am.ListAlerts(context.Background(), AlertFilters{
+		Active:   &active,
+		Silenced: &silenced,
+		Inhibited: &inhibited,
+	})
+	if err != nil || len(alerts) == 0 {
+		return ""
+	}
+
+	// Count by severity
+	severities := make(map[string]int)
+	for _, a := range alerts {
+		sev := a.Labels["severity"]
+		if sev == "" {
+			sev = "unknown"
+		}
+		severities[sev]++
+	}
+
+	var parts []string
+	// Show critical first if present
+	if n, ok := severities["critical"]; ok {
+		parts = append(parts, fmt.Sprintf("%d critical", n))
+		delete(severities, "critical")
+	}
+	if n, ok := severities["warning"]; ok {
+		parts = append(parts, fmt.Sprintf("%d warning", n))
+		delete(severities, "warning")
+	}
+	for sev, n := range severities {
+		parts = append(parts, fmt.Sprintf("%d %s", n, sev))
+	}
+
+	return fmt.Sprintf("ALERT STATUS: %d active alert(s) firing (%s). Use list_alerts for details. Let the user know about this.",
+		len(alerts), strings.Join(parts, ", "))
+}
+
 // RegisterHandlers registers all monitoring tool handlers on the MCP server.
 func RegisterHandlers(server *mcp.Server, prom *PrometheusClient, am *AlertmanagerClient) {
 	server.RegisterTool(listAlertsTool(), makeListAlertsHandler(am))