lntest+routing: update best height after graph pruning

It seems #5246 introduced a subtle bug that lead to the error "out of
order block: expecting height=1, got height=XXX" some times during
startup. Apparently it can happen that during pruning of the graph tip
some blocks can come in before we start our chain view and the new block
subscription. By querying the chain backend for the best height before
syncing with the graph we ensure that we never miss a block.

lntest/harness.go

@@ -177,9 +177,16 @@ func (n *NetworkHarness) SetUp(testCase string, lndArgs []string) error {
 	default:
 	}
 
+	// First, make a connection between the two nodes. This will wait until
+	// both nodes are fully started since the Connect RPC is guarded behind
+	// the server.Started() flag that waits for all subsystems to be ready.
+	ctxb := context.Background()
+	if err := n.ConnectNodes(ctxb, n.Alice, n.Bob); err != nil {
+		return err
+	}
+
 	// Load up the wallets of the seeder nodes with 10 outputs of 1 BTC
 	// each.
-	ctxb := context.Background()
 	addrReq := &lnrpc.NewAddressRequest{
 		Type: lnrpc.AddressType_WITNESS_PUBKEY_HASH,
 	}
@@ -216,8 +223,13 @@ func (n *NetworkHarness) SetUp(testCase string, lndArgs []string) error {
 		return err
 	}
 
-	// Finally, make a connection between both of the nodes.
+	// Now we want to wait for the nodes to catch up.
-	if err := n.ConnectNodes(ctxb, n.Alice, n.Bob); err != nil {
+	ctxt, cancel := context.WithTimeout(ctxb, DefaultTimeout)
+	defer cancel()
+	if err := n.Alice.WaitForBlockchainSync(ctxt); err != nil {
+		return err
+	}
+	if err := n.Bob.WaitForBlockchainSync(ctxt); err != nil {
 		return err
 	}
 

routing/router.go

@@ -563,6 +563,14 @@ func (r *ChannelRouter) Start() error {
 			}
 		}
 
+		// The graph pruning might have taken a while and there could be
+		// new blocks available.
+		bestHash, bestHeight, err = r.cfg.Chain.GetBestBlock()
+		if err != nil {
+			return err
+		}
+		r.bestHeight = uint32(bestHeight)
+
 		// Before we begin normal operation of the router, we first need
 		// to synchronize the channel graph to the latest state of the
 		// UTXO set.