feat: sample recent business events

internal/storage/mysql/operational_metrics.go

@@ -8,6 +8,7 @@ import (
 )
 
 const operationalMetricSampleLimit = 10000
+const operationalMetricEventWindow = 5 * time.Minute
 
 // OperationalSnapshot 是进程观测使用的有限数据库快照。
 // Counts 只包含固定状态的有界计数；达到上限时 Truncated 为 true，不能解释为精确总量。
@@ -26,12 +27,15 @@ type OperationalSnapshot struct {
 	WorkflowOldestAgeSeconds float64
 	// Truncated 表示至少一个状态达到有界采样上限。
 	Truncated bool
+	// RecentEvents 是固定事件类别在最近窗口内的有界数量。
+	RecentEvents map[string]uint64
 }
 
 var (
 	operationalTaskStates     = []string{"WAITING", "LEASED", "RUNNING", "NEEDS_REVIEW", "SUCCEEDED", "FAILED", "CANCELLED"}
 	operationalDeliveryStates = []string{"PENDING", "LEASED", "ACKED", "EXPIRED"}
 	operationalWorkflowStates = []string{"RUNNING", "WAITING", "CANCELLING", "NEEDS_REVIEW", "SUCCEEDED", "FAILED", "CANCELLED"}
+	operationalEventTypes     = []string{"task.accepted", "task.started", "task.succeeded", "task.failed", "task.needs_review", "task.requeued", "workflow.started", "workflow.advanced", "workflow.recovered", "workflow.blocked", "workflow.stopped"}
 )
 
 // ReadOperationalSnapshot performs only bounded, indexed reads. It is intended
@@ -68,11 +72,16 @@ func ReadOperationalSnapshot(ctx context.Context, db *sql.DB) (OperationalSnapsh
 	if err != nil {
 		return OperationalSnapshot{}, err
 	}
+	events, eventTruncated, err := boundedRecentEventCounts(ctx, db, now)
+	if err != nil {
+		return OperationalSnapshot{}, err
+	}
 	return OperationalSnapshot{
 		TaskStates: tasks, TaskOldestAgeSeconds: taskAge,
 		DeliveryStates: deliveries, DeliveryOldestAgeSeconds: deliveryAge,
 		WorkflowStates: workflows, WorkflowOldestAgeSeconds: workflowAge,
-		Truncated: taskTruncated || deliveryTruncated || workflowTruncated,
+		RecentEvents: events,
+		Truncated:    taskTruncated || deliveryTruncated || workflowTruncated || eventTruncated,
 	}, nil
 }
 
@@ -102,6 +111,25 @@ func boundedStateCounts(ctx context.Context, db *sql.DB, table, index string, st
 	return counts, truncated, nil
 }
 
+func boundedRecentEventCounts(ctx context.Context, db *sql.DB, now time.Time) (map[string]uint64, bool, error) {
+	counts := make(map[string]uint64, len(operationalEventTypes))
+	truncated := false
+	cutoff := now.Add(-operationalMetricEventWindow)
+	for _, eventType := range operationalEventTypes {
+		query := "SELECT COUNT(*) FROM (SELECT id FROM orbit_events FORCE INDEX (ix_event_observe_type_occurred) WHERE type=? AND occurred_at>=? LIMIT ?) AS bounded"
+		var n uint64
+		if err := db.QueryRowContext(ctx, query, eventType, cutoff, operationalMetricSampleLimit+1).Scan(&n); err != nil {
+			return nil, false, err
+		}
+		if n > operationalMetricSampleLimit {
+			n = operationalMetricSampleLimit
+			truncated = true
+		}
+		counts[eventType] = n
+	}
+	return counts, truncated, nil
+}
+
 func oldestAge(ctx context.Context, db *sql.DB, table, index string, states []string, column string, now time.Time) (float64, error) {
 	placeholders := "?"
 	args := make([]any, 0, len(states))