feat: sample recent business events

internal/observability/business.go

@@ -23,6 +23,8 @@ type BusinessSnapshot struct {
 	WorkflowOldestAgeSeconds float64
 	// Truncated 是否至少有一类状态达到采样上限。
 	Truncated bool
+	// RecentEvents 固定事件类别在最近窗口内的有界数量。
+	RecentEvents map[string]uint64
 }
 
 // RecordBusinessSnapshot records one bounded database sample. A failed sample
@@ -53,6 +55,9 @@ func (r *Registry) RecordBusinessSnapshot(snapshot BusinessSnapshot, started tim
 	for _, state := range workflowStates {
 		r.SetGauge("orbit_weave_workflows_state", float64(snapshot.WorkflowStates[state]), Labels{"state": state})
 	}
+	for _, eventType := range eventTypes {
+		r.SetGauge("orbit_business_events_recent", float64(snapshot.RecentEvents[eventType]), Labels{"event": eventType})
+	}
 	r.SetGauge("orbit_pulse_tasks_oldest_age_seconds", snapshot.TaskOldestAgeSeconds, nil)
 	r.SetGauge("orbit_result_delivery_oldest_age_seconds", snapshot.DeliveryOldestAgeSeconds, nil)
 	r.SetGauge("orbit_weave_workflow_oldest_age_seconds", snapshot.WorkflowOldestAgeSeconds, nil)