config+itest: move custom message override

It turns out the custom message override that should've allowed tapd to
send custom p2p wire messages never worked, because we set the value
after calling into lnd.ValidateConfig() which actually injects the value
into the lnwire package. We now move the code and also create an itest
for it (we should be able to try funding multiple times after each
other, as each attempt should be cleaned up by the receiver when they
receive the error message).

config.go

@@ -400,19 +400,6 @@ func loadAndValidateConfig(interceptor signal.Interceptor) (*Config, error) {
 		cfg.Lnd.RPCMiddleware.Enable = true
 	}
 
-	// For the integration of tapd with lnd, we need to allow tapd to send
-	// custom error messages to peers through the SendCustomMessage RPC in
-	// lnd. Since the error messages aren't in the custom range, we
-	// explicitly need to allow them. This isn't currently needed in remote
-	// mode, because custom channels are only available if both lnd and tapd
-	// are running in integrated mode.
-	if !cfg.lndRemote {
-		cfg.Lnd.ProtocolOptions.CustomMessage = append(
-			cfg.Lnd.ProtocolOptions.CustomMessage,
-			lnwire.MsgError,
-		)
-	}
-
 	// Validate the lightning-terminal config options.
 	litDir := lnd.CleanAndExpandPath(preCfg.LitDir)
 	cfg.LetsEncryptDir = lncfg.CleanAndExpandPath(cfg.LetsEncryptDir)
@@ -620,6 +607,19 @@ func loadConfigFile(preCfg *Config, interceptor signal.Interceptor) (*Config,
 	// configuration is fully valid. This also sets up the main logger that
 	// logs to a sub-directory in the .lnd folder.
 	case ModeIntegrated:
+		// For the integration of tapd with lnd, we need to allow tapd
+		// to send custom error messages to peers through the
+		// SendCustomMessage RPC in lnd. Since the error messages aren't
+		// in the custom range, we explicitly need to allow them. This
+		// isn't currently needed in remote mode, because custom
+		// channels are only available if both lnd and tapd are running
+		// in integrated mode. We need to set this value before we call
+		// lnd.ValidateConfig() below, because that's what's going to
+		// inject these values into the lnwire package.
+		cfg.Lnd.ProtocolOptions.CustomMessage = append(
+			cfg.Lnd.ProtocolOptions.CustomMessage, lnwire.MsgError,
+		)
+
 		var err error
 		cfg.Lnd, err = lnd.ValidateConfig(
 			*cfg.Lnd, interceptor, fileParser, flagParser,

itest/litd_custom_channels_test.go

@@ -6,6 +6,7 @@ import (
 	"slices"
 	"time"
 
+	"github.com/btcsuite/btcd/btcutil"
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
 	"github.com/lightninglabs/taproot-assets/itest"
 	"github.com/lightninglabs/taproot-assets/proof"
@@ -1160,6 +1161,36 @@ func testCustomChannelsForceClose(_ context.Context, net *NetworkHarness,
 	syncUniverses(t.t, charlieTap, dave)
 	t.Logf("Universes synced between all nodes, distributing assets...")
 
+	// Before we actually create the asset channel, we want to make sure
+	// that failed attempts of creating a channel (e.g. due to insufficient
+	// on-chain funds) are cleaned up properly on the recipient side.
+	// We do this by sending all of Charlie's coins to a burn address then
+	// just sending him 50k sats, which isn't enough to fund a channel.
+	_, err = charlie.LightningClient.SendCoins(
+		ctxb, &lnrpc.SendCoinsRequest{
+			Addr:             burnAddr,
+			SendAll:          true,
+			MinConfs:         0,
+			SpendUnconfirmed: true,
+		},
+	)
+	require.NoError(t.t, err)
+	net.SendCoins(t.t, 50_000, charlie)
+
+	// The attempt should fail. But the recipient should receive the error,
+	// clean up the state and allow Charlie to try again after acquiring
+	// more funds.
+	_, err = charlieTap.FundChannel(ctxb, &tchrpc.FundChannelRequest{
+		AssetAmount:        fundingAmount,
+		AssetId:            assetID,
+		PeerPubkey:         dave.PubKey[:],
+		FeeRateSatPerVbyte: 5,
+	})
+	require.ErrorContains(t.t, err, "not enough witness outputs to create")
+
+	// Now we'll fund the channel with the correct amount.
+	net.SendCoins(t.t, btcutil.SatoshiPerBitcoin, charlie)
+
 	// Next we can open an asset channel from Charlie -> Dave, then kick
 	// off the main scenario.
 	t.Logf("Opening asset channels...")