lnwallet: handle nonce init in ProcessChanSyncMsg

In this commit, we update the logic to handle nonce init in
ProcessChanSyncMsg. Once a channel is already open, this is where we'll
get the new nonce data from the remote party we'll use to gain the nonce
we need to sign for their next state.

lnwallet/channel.go

@@ -4092,8 +4092,6 @@ func (lc *LightningChannel) ProcessChanSyncMsg(
 	msg *lnwire.ChannelReestablish) ([]lnwire.Message, []models.CircuitKey,
 	[]models.CircuitKey, error) {
 
-	// TODO(roasbeef): need to replace w/ received nonces
-
 	// Now we'll examine the state we have, vs what was contained in the
 	// chain sync message. If we're de-synchronized, then we'll send a
 	// batch of messages which when applied will kick start the chain
@@ -4133,6 +4131,25 @@ func (lc *LightningChannel) ProcessChanSyncMsg(
 		}
 	}
 
+	// If this is a taproot channel, then we expect that the remote party
+	// has sent the next verification nonce. If they haven't, then we'll
+	// bail out, otherwise we'll init our local session then continue as
+	// normal.
+	switch {
+	case lc.channelState.ChanType.IsTaproot() && msg.LocalNonce == nil:
+		return nil, nil, nil, fmt.Errorf("remote verification nonce " +
+			"not sent")
+
+	case lc.channelState.ChanType.IsTaproot() && msg.LocalNonce != nil:
+		err := lc.InitRemoteMusigNonces(&musig2.Nonces{
+			PubNonce: *msg.LocalNonce,
+		})
+		if err != nil {
+			return nil, nil, nil, fmt.Errorf("unable to init "+
+				"remote nonce: %w", err)
+		}
+	}
+
 	// If we detect that this is is a restored channel, then we can skip a
 	// portion of the verification, as we already know that we're unable to
 	// proceed with any updates.
@@ -4210,12 +4227,12 @@ func (lc *LightningChannel) ProcessChanSyncMsg(
 			"while we have %v, we owe them a revocation",
 			msg.RemoteCommitTailHeight, localTailHeight)
 
-		revocationMsg, err := lc.generateRevocation(
-			localTailHeight - 1,
-		)
+		heightToRetransmit := localTailHeight - 1
+		revocationMsg, err := lc.generateRevocation(heightToRetransmit)
 		if err != nil {
 			return nil, nil, nil, err
 		}
+
 		updates = append(updates, revocationMsg)
 
 		// Next, as a precaution, we'll check a special edge case. If