sync: disable mesh agreement on mainnet (#5522)

the goal of mesh agreement is to download ballots and activations when partitions made individual progress.
such as in Partition_50_50 or 70_30 tests.

however on mainnet it creates unnecessary load by triggering queries to download atx. i suggest to disable that and wait for set reconciliation to fix it.

related: #5519

config/mainnet.go

@@ -187,6 +187,7 @@ func MainnetConfig() Config {
 			Standalone:               false,
 			GossipDuration:           50 * time.Second,
 			OutOfSyncThresholdLayers: 36, // 3h
+			DisableMeshAgreement:     true,
 			DisableAtxReconciliation: true,
 		},
 		Recovery: checkpoint.DefaultConfig(),

syncer/state_syncer.go

@@ -85,7 +85,7 @@ func (s *Syncer) processLayers(ctx context.Context) error {
 						Warning("failed to adopt peer opinions", lid, log.Err(err))
 				}
 			}
-			if s.IsSynced(ctx) {
+			if s.IsSynced(ctx) && !s.cfg.DisableMeshAgreement {
 				if err = s.checkMeshAgreement(ctx, lid, opinions); err != nil &&
 					errors.Is(err, errMeshHashDiverged) {
 					s.logger.WithContext(ctx).

syncer/syncer.go

@@ -28,6 +28,7 @@ type Config struct {
 	MaxStaleDuration         time.Duration `mapstructure:"maxstaleduration"`
 	Standalone               bool
 	GossipDuration           time.Duration `mapstructure:"gossipduration"`
+	DisableMeshAgreement     bool          `mapstructure:"disable-mesh-agreement"`
 	DisableAtxReconciliation bool          `mapstructure:"disable-atx-reconciliation"`
 	OutOfSyncThresholdLayers uint32        `mapstructure:"out-of-sync-threshold"`
 }