feat: implement transactional start slot metadata updates per provider

- Replace simple LatestSlot assignment with new updateStartSlot() function
  that properly handles per-provider slot tracking
- Implement transaction-based metadata updates using BeginTx/SetMetadata/CommitTx
  pattern for atomicity and consistency
- Set LatestSlots for each relay provider instead of single LatestSlot field
- Add proper error handling with context cancellation on transaction failure

Author: xav

services/bids/standard/service.go

@@ -84,8 +84,12 @@ func (s *Service) onStart(ctx context.Context,
 	if err != nil {
 		return errors.Wrap(err, "failed to obtain metadata")
 	}
+
 	if startSlot >= 0 {
-		md.LatestSlot = startSlot - 1
+		err := updateStartSlot(ctx, s, md, startSlot)
+		if err != nil {
+			return err
+		}
 	}
 
 	log.Trace().Msg("Running initial catchup")
@@ -110,6 +114,34 @@ func (s *Service) onStart(ctx context.Context,
 	return nil
 }
 
+func updateStartSlot(ctx context.Context, s *Service, md *metadata, startSlot int64) error {
+	md.mu.Lock()
+	defer md.mu.Unlock()
+
+	opCtx, cancel, err := s.receivedBidsSetter.BeginTx(ctx)
+	if err != nil {
+		return errors.Wrap(err, "failed to begin transaction for metadata update")
+	}
+
+	for _, prov := range s.receivedBidTracesProviders {
+		name := prov.Name()
+		if cur, ok := md.LatestSlots[name]; !ok || cur < startSlot-1 {
+			md.LatestSlots[name] = startSlot - 1
+		}
+	}
+
+	if err := s.setMetadata(ctx, md); err != nil {
+		return errors.Wrap(err, "failed to set metadata")
+	}
+
+	if err := s.receivedBidsSetter.CommitTx(opCtx); err != nil {
+		cancel()
+		return errors.Wrap(err, "failed to commit metadata transaction")
+	}
+
+	return nil
+}
+
 func (s *Service) onTick(ctx context.Context, _ any) {
 	// Only allow 1 handler to be active.
 	acquired := s.activitySem.TryAcquire(1)