graph/db: add v2 channel announcement fields to ChannelEdgeInfo

This commit extends ChannelEdgeInfo to support v2 (taproot) channel
announcements by adding:
- MerkleRootHash for the optional Merkle tree commitment
- ExtraSignedFields for additional signed TLV fields
- ChannelV2Fields struct to encapsulate v2-specific optional fields
- NewV2Channel constructor for creating v2 channel edges
- FundingPKScript handling for MuSig2 key aggregation with optional
  taproot tweaks

graph/db/models/channel_edge_info_test.go

@@ -0,0 +1,147 @@
+package models
+
+import (
+	"testing"
+
+	"github.com/btcsuite/btcd/btcec/v2"
+	"github.com/btcsuite/btcd/btcec/v2/schnorr/musig2"
+	"github.com/btcsuite/btcd/chaincfg/chainhash"
+	"github.com/lightningnetwork/lnd/fn/v2"
+	"github.com/lightningnetwork/lnd/input"
+	"github.com/lightningnetwork/lnd/lnwire"
+	"github.com/lightningnetwork/lnd/routing/route"
+	"github.com/stretchr/testify/require"
+)
+
+// TestFundingPKScriptV2 tests the FundingPKScript method for v2 channels
+// which uses MuSig2 key aggregation.
+func TestFundingPKScriptV2(t *testing.T) {
+	t.Parallel()
+
+	// Generate two test keys for bitcoin keys.
+	privKey1, err := btcec.NewPrivateKey()
+	require.NoError(t, err)
+	pubKey1 := privKey1.PubKey()
+
+	privKey2, err := btcec.NewPrivateKey()
+	require.NoError(t, err)
+	pubKey2 := privKey2.PubKey()
+
+	// Convert to route.Vertex format.
+	var btcKey1, btcKey2 route.Vertex
+	copy(btcKey1[:], pubKey1.SerializeCompressed())
+	copy(btcKey2[:], pubKey2.SerializeCompressed())
+
+	// Create a test merkle root.
+	var merkleRoot chainhash.Hash
+	copy(merkleRoot[:], []byte("test-merkle-root-hash-32-bytes!"))
+
+	t.Run("v2 with btc keys, no merkle root (BIP86)", func(t *testing.T) {
+		t.Parallel()
+
+		edge := &ChannelEdgeInfo{
+			Version:          lnwire.GossipVersion2,
+			BitcoinKey1Bytes: fn.Some(btcKey1),
+			BitcoinKey2Bytes: fn.Some(btcKey2),
+		}
+
+		pkScript, err := edge.FundingPKScript()
+		require.NoError(t, err)
+		require.NotEmpty(t, pkScript)
+
+		// Verify it's a valid taproot script (OP_1 <32-byte-key>).
+		require.Len(t, pkScript, 34)
+		require.Equal(t, byte(0x51), pkScript[0]) // OP_1
+
+		// Manually compute expected script using BIP86 tweak.
+		combinedKey, _, _, err := musig2.AggregateKeys(
+			[]*btcec.PublicKey{pubKey1, pubKey2}, true,
+			musig2.WithBIP86KeyTweak(),
+		)
+		require.NoError(t, err)
+
+		expectedScript, err := input.PayToTaprootScript(
+			combinedKey.FinalKey,
+		)
+		require.NoError(t, err)
+		require.Equal(t, expectedScript, pkScript)
+	})
+
+	t.Run("v2 with bitcoin keys and merkle root", func(t *testing.T) {
+		t.Parallel()
+
+		edge := &ChannelEdgeInfo{
+			Version:          lnwire.GossipVersion2,
+			BitcoinKey1Bytes: fn.Some(btcKey1),
+			BitcoinKey2Bytes: fn.Some(btcKey2),
+			MerkleRootHash:   fn.Some(merkleRoot),
+		}
+
+		pkScript, err := edge.FundingPKScript()
+		require.NoError(t, err)
+		require.NotEmpty(t, pkScript)
+
+		// Verify it's a valid taproot script.
+		require.Len(t, pkScript, 34)
+		require.Equal(t, byte(0x51), pkScript[0]) // OP_1
+
+		// Manually compute expected script with taproot tweak.
+		combinedKey, _, _, err := musig2.AggregateKeys(
+			[]*btcec.PublicKey{pubKey1, pubKey2}, true,
+			musig2.WithTaprootKeyTweak(merkleRoot[:]),
+		)
+		require.NoError(t, err)
+
+		expectedScript, err := input.PayToTaprootScript(
+			combinedKey.FinalKey,
+		)
+		require.NoError(t, err)
+		require.Equal(t, expectedScript, pkScript)
+	})
+
+	t.Run("v2 no btc keys returns stored script", func(t *testing.T) {
+		t.Parallel()
+
+		storedScript := []byte{0x51, 0x20} // OP_1 + push 32
+		storedScript = append(storedScript, make([]byte, 32)...)
+
+		edge := &ChannelEdgeInfo{
+			Version:       lnwire.GossipVersion2,
+			FundingScript: fn.Some(storedScript),
+		}
+
+		pkScript, err := edge.FundingPKScript()
+		require.NoError(t, err)
+		require.Equal(t, storedScript, pkScript)
+	})
+
+	t.Run("v2 no btc keys and no stored script errors", func(t *testing.T) {
+		t.Parallel()
+
+		edge := &ChannelEdgeInfo{
+			Version: lnwire.GossipVersion2,
+		}
+
+		_, err := edge.FundingPKScript()
+		require.Error(t, err)
+		require.Contains(t, err.Error(), "expected a funding pk script")
+	})
+
+	t.Run("v2 one btc key returns stored script", func(t *testing.T) {
+		t.Parallel()
+
+		storedScript := []byte{0x51, 0x20}
+		storedScript = append(storedScript, make([]byte, 32)...)
+
+		// Only key1 set, key2 missing.
+		edge := &ChannelEdgeInfo{
+			Version:          lnwire.GossipVersion2,
+			BitcoinKey1Bytes: fn.Some(btcKey1),
+			FundingScript:    fn.Some(storedScript),
+		}
+
+		pkScript, err := edge.FundingPKScript()
+		require.NoError(t, err)
+		require.Equal(t, storedScript, pkScript)
+	})
+}