chanstate: move taproot channel helpers

diff --git a/channeldb/channel.go b/channeldb/channel.go
index eae8f2f..8985b70 100644
--- a/channeldb/channel.go
+++ b/channeldb/channel.go
@@ -2,7 +2,6 @@ package channeldb
 
 import (
 	"bytes"
-	"crypto/hmac"
 	"crypto/sha256"
 	"encoding/binary"
 	"errors"
@@ -12,7 +11,6 @@ import (
 	"sync"
 
 	"github.com/btcsuite/btcd/btcec/v2"
-	"github.com/btcsuite/btcd/btcec/v2/schnorr/musig2"
 	"github.com/btcsuite/btcd/btcutil/v2"
 	"github.com/btcsuite/btcd/chainhash/v2"
 	"github.com/btcsuite/btcd/wire/v2"
@@ -32,16 +30,18 @@ import (
 )
 
 const (
-	// AbsoluteThawHeightThreshold is the threshold at which a thaw height
-	// begins to be interpreted as an absolute block height, rather than a
-	// relative one.
-	AbsoluteThawHeightThreshold uint32 = 500000
-
 	// HTLCBlindingPointTLV is the tlv type used for storing blinding
 	// points with HTLCs.
 	HTLCBlindingPointTLV tlv.Type = 0
 )
 
+const (
+	// AbsoluteThawHeightThreshold is the threshold at which a thaw height
+	// begins to be interpreted as an absolute block height, rather than a
+	// relative one.
+	AbsoluteThawHeightThreshold = cstate.AbsoluteThawHeightThreshold
+)
+
 var (
 	// closedChannelBucket stores summarization information concerning
 	// previously open, but now closed channels.
@@ -1672,63 +1672,14 @@ func (c *OpenChannel) SecondCommitmentPoint() (*btcec.PublicKey, error) {
 }
 
 var (
-	// taprootRevRootKey is the key used to derive the revocation root for
-	// the taproot nonces. This is done via HMAC of the existing revocation
-	// root.
-	taprootRevRootKey = []byte("taproot-rev-root")
-)
-
-// DeriveMusig2Shachain derives a shachain producer for the taproot channel
-// from normal shachain revocation root.
-func DeriveMusig2Shachain(revRoot shachain.Producer) (shachain.Producer, error) { //nolint:ll
-	// In order to obtain the revocation root hash to create the taproot
-	// revocation, we'll encode the producer into a buffer, then use that
-	// to derive the shachain root needed.
-	var rootHashBuf bytes.Buffer
-	if err := revRoot.Encode(&rootHashBuf); err != nil {
-		return nil, fmt.Errorf("unable to encode producer: %w", err)
-	}
-
-	revRootHash := chainhash.HashH(rootHashBuf.Bytes())
-
-	// For taproot channel types, we'll also generate a distinct shachain
-	// root using the same seed information. We'll use this to generate
-	// verification nonces for the channel. We'll bind with this a simple
-	// hmac.
-	taprootRevHmac := hmac.New(sha256.New, taprootRevRootKey)
-	if _, err := taprootRevHmac.Write(revRootHash[:]); err != nil {
-		return nil, err
-	}
-
-	taprootRevRoot := taprootRevHmac.Sum(nil)
+	// DeriveMusig2Shachain derives a shachain producer for the taproot
+	// channel from normal shachain revocation root.
+	DeriveMusig2Shachain = cstate.DeriveMusig2Shachain
 
-	// Once we have the root, we can then generate our shachain producer
-	// and from that generate the per-commitment point.
-	return shachain.NewRevocationProducerFromBytes(
-		taprootRevRoot,
-	)
-}
-
-// NewMusigVerificationNonce generates the local or verification nonce for
-// another musig2 session. In order to permit our implementation to not have to
-// write any secret nonce state to disk, we'll use the _next_ shachain
-// pre-image as our primary randomness source. When used to generate the nonce
-// again to broadcast our commitment hte current height will be used.
-func NewMusigVerificationNonce(pubKey *btcec.PublicKey, targetHeight uint64,
-	shaGen shachain.Producer) (*musig2.Nonces, error) {
-
-	// Now that we know what height we need, we'll grab the shachain
-	// pre-image at the target destination.
-	nextPreimage, err := shaGen.AtIndex(targetHeight)
-	if err != nil {
-		return nil, err
-	}
-
-	shaChainRand := musig2.WithCustomRand(bytes.NewBuffer(nextPreimage[:]))
-	pubKeyOpt := musig2.WithPublicKey(pubKey)
-
-	return musig2.GenNonces(pubKeyOpt, shaChainRand)
-}
+	// NewMusigVerificationNonce generates the local or verification nonce
+	// for another musig2 session.
+	NewMusigVerificationNonce = cstate.NewMusigVerificationNonce
+)
 
 // ChanSyncMsg returns the ChannelReestablish message that should be sent upon
 // reconnection with the remote peer that we're maintaining this channel with.
diff --git a/chanstate/taproot.go b/chanstate/taproot.go
new file mode 100644
index 0000000..cfa3310
--- /dev/null
+++ b/chanstate/taproot.go
@@ -0,0 +1,79 @@
+package chanstate
+
+import (
+	"bytes"
+	"crypto/hmac"
+	"crypto/sha256"
+	"fmt"
+
+	"github.com/btcsuite/btcd/btcec/v2"
+	"github.com/btcsuite/btcd/btcec/v2/schnorr/musig2"
+	"github.com/btcsuite/btcd/chainhash/v2"
+	"github.com/lightningnetwork/lnd/shachain"
+)
+
+const (
+	// AbsoluteThawHeightThreshold is the threshold at which a thaw height
+	// begins to be interpreted as an absolute block height, rather than a
+	// relative one.
+	AbsoluteThawHeightThreshold uint32 = 500000
+)
+
+var (
+	// taprootRevRootKey is the key used to derive the revocation root for
+	// the taproot nonces. This is done via HMAC of the existing revocation
+	// root.
+	taprootRevRootKey = []byte("taproot-rev-root")
+)
+
+// DeriveMusig2Shachain derives a shachain producer for the taproot channel
+// from normal shachain revocation root.
+func DeriveMusig2Shachain(revRoot shachain.Producer) (shachain.Producer, error) { //nolint:ll
+	// In order to obtain the revocation root hash to create the taproot
+	// revocation, we'll encode the producer into a buffer, then use that
+	// to derive the shachain root needed.
+	var rootHashBuf bytes.Buffer
+	if err := revRoot.Encode(&rootHashBuf); err != nil {
+		return nil, fmt.Errorf("unable to encode producer: %w", err)
+	}
+
+	revRootHash := chainhash.HashH(rootHashBuf.Bytes())
+
+	// For taproot channel types, we'll also generate a distinct shachain
+	// root using the same seed information. We'll use this to generate
+	// verification nonces for the channel. We'll bind with this a simple
+	// hmac.
+	taprootRevHmac := hmac.New(sha256.New, taprootRevRootKey)
+	if _, err := taprootRevHmac.Write(revRootHash[:]); err != nil {
+		return nil, err
+	}
+
+	taprootRevRoot := taprootRevHmac.Sum(nil)
+
+	// Once we have the root, we can then generate our shachain producer
+	// and from that generate the per-commitment point.
+	return shachain.NewRevocationProducerFromBytes(
+		taprootRevRoot,
+	)
+}
+
+// NewMusigVerificationNonce generates the local or verification nonce for
+// another musig2 session. In order to permit our implementation to not have to
+// write any secret nonce state to disk, we'll use the _next_ shachain
+// pre-image as our primary randomness source. When used to generate the nonce
+// again to broadcast our commitment hte current height will be used.
+func NewMusigVerificationNonce(pubKey *btcec.PublicKey, targetHeight uint64,
+	shaGen shachain.Producer) (*musig2.Nonces, error) {
+
+	// Now that we know what height we need, we'll grab the shachain
+	// pre-image at the target destination.
+	nextPreimage, err := shaGen.AtIndex(targetHeight)
+	if err != nil {
+		return nil, err
+	}
+
+	shaChainRand := musig2.WithCustomRand(bytes.NewBuffer(nextPreimage[:]))
+	pubKeyOpt := musig2.WithPublicKey(pubKey)
+
+	return musig2.GenNonces(pubKeyOpt, shaChainRand)
+}