fixup to match spec, move constants to common location

node/impl/full/sync.go

@@ -4,6 +4,7 @@ import (
 	"context"
 
 	"github.com/filecoin-project/lotus/api"
+	"github.com/filecoin-project/lotus/build"
 	"github.com/filecoin-project/lotus/chain"
 	"github.com/filecoin-project/lotus/chain/types"
 	cid "github.com/ipfs/go-cid"
@@ -76,7 +77,7 @@ func (a *SyncAPI) SyncSubmitBlock(ctx context.Context, blk *types.BlockMsg) erro
 	}
 
 	// TODO: anything else to do here?
-	return a.PubSub.Publish("/fil/blocks", b)
+	return a.PubSub.Publish(build.MessagesTopic, b)
 }
 
 func (a *SyncAPI) SyncIncomingBlocks(ctx context.Context) (<-chan *types.BlockHeader, error) {