contractcourt: properly detect RBF coop close transactions

This commit fixes an issue where we did not properly detect and
therefore record the coop close transaction if it used the newer
RBF coop close v2 scheme. This only affects coop closes of
taproot channels today.

Author: ProofOfKeags

contractcourt/chain_watcher.go

@@ -12,6 +12,7 @@ import (
 	"github.com/btcsuite/btcd/btcutil"
 	"github.com/btcsuite/btcd/chaincfg"
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
+	"github.com/btcsuite/btcd/mempool"
 	"github.com/btcsuite/btcd/txscript"
 	"github.com/btcsuite/btcd/wire"
 	"github.com/davecgh/go-spew/spew"
@@ -689,7 +690,10 @@ func (c *chainWatcher) closeObserver(spendNtfn *chainntnfs.SpendEvent) {
 		// sequence number that's finalized. This won't happen with
 		// regular commitment transactions due to the state hint
 		// encoding scheme.
-		if commitTxBroadcast.TxIn[0].Sequence == wire.MaxTxInSequenceNum {
+		switch commitTxBroadcast.TxIn[0].Sequence {
+		case wire.MaxTxInSequenceNum:
+			fallthrough
+		case mempool.MaxRBFSequence:
 			// TODO(roasbeef): rare but possible, need itest case
 			// for
 			err := c.dispatchCooperativeClose(commitSpend)