feat: expose mysql transaction retry metrics

internal/observability/runtime.go

@@ -102,6 +102,9 @@ func (r *Registry) RecordBatch(component string, started time.Time, err error) {
 
 // RecordDatabase reads the local connection-pool snapshot; it issues no SQL.
 func (r *Registry) RecordDatabase(s sql.DBStats) {
+	if r == nil {
+		return
+	}
 	r.SetGauge("orbit_db_connections_open", float64(s.OpenConnections), nil)
 	r.SetGauge("orbit_db_connections_in_use", float64(s.InUse), nil)
 	r.SetGauge("orbit_db_connections_idle", float64(s.Idle), nil)
@@ -109,3 +112,18 @@ func (r *Registry) RecordDatabase(s sql.DBStats) {
 	r.SetCounter("orbit_db_wait_count_total", float64(s.WaitCount), nil)
 	r.SetCounter("orbit_db_wait_duration_seconds_total", s.WaitDuration.Seconds(), nil)
 }
+
+// TransactionStats 是本进程提交前事务重试的累计观测值。
+type TransactionStats struct {
+	Retries   uint64 // 已实际执行的重试次数。
+	Exhausted uint64 // 达到重试上限的事务次数。
+}
+
+// RecordTransactionStats records bounded database transaction retry counters.
+func (r *Registry) RecordTransactionStats(stats TransactionStats) {
+	if r == nil {
+		return
+	}
+	r.SetCounter("orbit_db_transaction_retries_total", float64(stats.Retries), nil)
+	r.SetCounter("orbit_db_transaction_retry_exhausted_total", float64(stats.Exhausted), nil)
+}