channeldb: update ChanSyncMsg to populate nonce info

In this commit, we update the ChanSyncMsg to populate nonce information.
With this change, we can now hide nonce generation further down in the
pipeline and ensure that all callers will have the expected fields
populated.

channeldb/channel.go

@@ -1513,6 +1513,30 @@ func (c *OpenChannel) ChanSyncMsg() (*lnwire.ChannelReestablish, error) {
 		}
 	}
 
+	// If this is a taproot channel, then we'll need to generate our next
+	// verification nonce to send to the remote party. They'll use this to
+	// sign the next update to our commitment transaction.
+	var nextTaprootNonce *lnwire.Musig2Nonce
+	if c.ChanType.IsTaproot() {
+		taprootRevProducer, err := DeriveMusig2Shachain(
+			c.RevocationProducer,
+		)
+		if err != nil {
+			return nil, err
+		}
+
+		nextNonce, err := NewMusigVerificationNonce(
+			c.LocalChanCfg.MultiSigKey.PubKey,
+			nextLocalCommitHeight, taprootRevProducer,
+		)
+		if err != nil {
+			return nil, fmt.Errorf("unable to gen next "+
+				"nonce: %w", err)
+		}
+
+		nextTaprootNonce = (*lnwire.Musig2Nonce)(&nextNonce.PubNonce)
+	}
+
 	return &lnwire.ChannelReestablish{
 		ChanID: lnwire.NewChanIDFromOutPoint(
 			&c.FundingOutpoint,
@@ -1523,6 +1547,7 @@ func (c *OpenChannel) ChanSyncMsg() (*lnwire.ChannelReestablish, error) {
 		LocalUnrevokedCommitPoint: input.ComputeCommitmentPoint(
 			currentCommitSecret[:],
 		),
+		LocalNonce: nextTaprootNonce,
 	}, nil
 }