Add backwards-compatible parts of the official splicing protocol (#3261)

diff --git a/eclair-core/src/main/resources/reference.conf b/eclair-core/src/main/resources/reference.conf
index ba318db..e452e9b 100644
--- a/eclair-core/src/main/resources/reference.conf
+++ b/eclair-core/src/main/resources/reference.conf
@@ -109,7 +109,7 @@ eclair {
     funding {
       // Each RBF attempt adds more data that we need to store and process, so we want to limit our peers to a reasonable use of RBF.
       remote-rbf-limits {
-        max-attempts = 5 // maximum number of RBF attempts our peer is allowed to make
+        max-attempts = 10 // maximum number of RBF attempts our peer is allowed to make
         attempt-delta-blocks = 6 // minimum number of blocks between RBF attempts
       }
       // Duration after which we abort a channel creation. If our peer seems unresponsive and doesn't complete the
diff --git a/eclair-core/src/main/scala/fr/acinq/eclair/channel/Commitments.scala b/eclair-core/src/main/scala/fr/acinq/eclair/channel/Commitments.scala
index 901f45e..dd18fca 100644
--- a/eclair-core/src/main/scala/fr/acinq/eclair/channel/Commitments.scala
+++ b/eclair-core/src/main/scala/fr/acinq/eclair/channel/Commitments.scala
@@ -210,14 +210,14 @@ case class RemoteCommit(index: Long, spec: CommitmentSpec, txId: TxId, remotePer
     commitmentFormat match {
       case _: SegwitV0CommitmentFormat =>
         val sig = remoteCommitTx.sign(fundingKey, remoteFundingPubKey)
-        Right(CommitSig(channelParams.channelId, sig, htlcSigs.toList, batchSize))
+        Right(CommitSig(channelParams.channelId, commitInput.outPoint.txid, sig, htlcSigs.toList, batchSize))
       case _: SimpleTaprootChannelCommitmentFormat =>
         remoteNonce_opt match {
           case Some(remoteNonce) =>
             val localNonce = NonceGenerator.signingNonce(fundingKey.publicKey, remoteFundingPubKey, commitInput.outPoint.txid)
             remoteCommitTx.partialSign(fundingKey, remoteFundingPubKey, localNonce, Seq(localNonce.publicNonce, remoteNonce)) match {
               case Left(_) => Left(InvalidCommitNonce(channelParams.channelId, commitInput.outPoint.txid, index))
-              case Right(psig) => Right(CommitSig(channelParams.channelId, psig, htlcSigs.toList, batchSize))
+              case Right(psig) => Right(CommitSig(channelParams.channelId, commitInput.outPoint.txid, psig, htlcSigs.toList, batchSize))
             }
           case None => Left(MissingCommitNonce(channelParams.channelId, commitInput.outPoint.txid, index))
         }
@@ -650,7 +650,7 @@ case class Commitment(fundingTxIndex: Long,
           case None => return Left(MissingCommitNonce(params.channelId, fundingTxId, remoteCommit.index + 1))
         }
     }
-    val commitSig = CommitSig(params.channelId, sig, htlcSigs.toList, batchSize)
+    val commitSig = CommitSig(params.channelId, fundingTxId, sig, htlcSigs.toList, batchSize)
     val nextRemoteCommit = RemoteCommit(remoteCommit.index + 1, spec, remoteCommitTx.tx.txid, remoteNextPerCommitmentPoint)
     Right((copy(nextRemoteCommit_opt = Some(nextRemoteCommit)), commitSig))
   }
@@ -1089,9 +1089,11 @@ case class Commitments(channelParams: ChannelParams,
       case _: CommitSig if active.size > 1 => return Left(CommitSigCountMismatch(channelId, active.size, 1))
       case commitSig: CommitSig => Seq(commitSig)
     }
-    // Signatures are sent in order (most recent first), calling `zip` will drop trailing sigs that are for deactivated/pruned commitments.
     val commitKeys = LocalCommitmentKeys(channelParams, channelKeys, localCommitIndex + 1)
-    val active1 = active.zip(sigs).map { case (commitment, commit) =>
+    val active1 = active.zipWithIndex.map { case (commitment, idx) =>
+      // If the funding_txid isn't provided, we assume that signatures are sent in order (most recent first).
+      // This matches the behavior of peers who only support the experimental version of splicing.
+      val commit = sigs.find(_.fundingTxId_opt.contains(commitment.fundingTxId)).getOrElse(sigs(idx))
       commitment.receiveCommit(channelParams, channelKeys, commitKeys, changes, commit) match {
         case Left(f) => return Left(f)
         case Right(commitment1) => commitment1
diff --git a/eclair-core/src/main/scala/fr/acinq/eclair/channel/fund/InteractiveTxBuilder.scala b/eclair-core/src/main/scala/fr/acinq/eclair/channel/fund/InteractiveTxBuilder.scala
index bd48a66..5edd456 100644
--- a/eclair-core/src/main/scala/fr/acinq/eclair/channel/fund/InteractiveTxBuilder.scala
+++ b/eclair-core/src/main/scala/fr/acinq/eclair/channel/fund/InteractiveTxBuilder.scala
@@ -949,7 +949,7 @@ private class InteractiveTxBuilder(replyTo: ActorRef[InteractiveTxBuilder.Respon
           case Right(localSigOfRemoteTx) =>
             val htlcSignatures = sortedHtlcTxs.map(_.localSig(remoteCommitmentKeys)).toList
             log.info(s"built remote commit number=${purpose.remoteCommitIndex} toLocalMsat=${remoteSpec.toLocal.toLong} toRemoteMsat=${remoteSpec.toRemote.toLong} htlc_in={} htlc_out={} feeratePerKw=${remoteSpec.commitTxFeerate} txid=${remoteCommitTx.tx.txid} fundingTxId=${fundingTx.txid}", remoteSpec.htlcs.collect(DirectedHtlc.outgoing).map(_.id).mkString(","), remoteSpec.htlcs.collect(DirectedHtlc.incoming).map(_.id).mkString(","))
-            val localCommitSig = CommitSig(fundingParams.channelId, localSigOfRemoteTx, htlcSignatures, batchSize = 1)
+            val localCommitSig = CommitSig(fundingParams.channelId, fundingTx.txid, localSigOfRemoteTx, htlcSignatures, batchSize = 1)
             val localCommit = UnsignedLocalCommit(purpose.localCommitIndex, localSpec, localCommitTx.tx.txid)
             val remoteCommit = RemoteCommit(purpose.remoteCommitIndex, remoteSpec, remoteCommitTx.tx.txid, purpose.remotePerCommitmentPoint)
             signFundingTx(completeTx, remoteFundingNonce_opt, remoteCommitNonces_opt.map(_.nextCommitNonce), localCommitSig, localCommit, remoteCommit)
diff --git a/eclair-core/src/main/scala/fr/acinq/eclair/io/PeerConnection.scala b/eclair-core/src/main/scala/fr/acinq/eclair/io/PeerConnection.scala
index 4ecd648..0083db4 100644
--- a/eclair-core/src/main/scala/fr/acinq/eclair/io/PeerConnection.scala
+++ b/eclair-core/src/main/scala/fr/acinq/eclair/io/PeerConnection.scala
@@ -208,7 +208,10 @@ class PeerConnection(keyPair: KeyPair, conf: PeerConnection.Conf, switchboard: A
 
       case Event(msg: LightningMessage, d: ConnectedData) if sender() != d.transport => // if the message doesn't originate from the transport, it is an outgoing message
         msg match {
-          case batch: CommitSigBatch => batch.messages.foreach(msg => d.transport forward msg)
+          case batch: CommitSigBatch =>
+            // We insert a start_batch message to let our peer know how many commit_sig they will receive.
+            d.transport forward StartBatch.commitSigBatch(batch.channelId, batch.batchSize)
+            batch.messages.foreach(msg => d.transport forward msg)
           case msg => d.transport forward msg
         }
         msg match {
@@ -347,8 +350,51 @@ class PeerConnection(keyPair: KeyPair, conf: PeerConnection.Conf, switchboard: A
         // We immediately forward messages to the peer, unless they are part of a batch, in which case we wait to
         // receive the whole batch before forwarding.
         msg match {
+          case msg: StartBatch =>
+            if (!msg.messageType_opt.contains(132)) {
+              log.debug("ignoring start_batch: we only support batching commit_sig messages")
+              d.transport ! Warning(msg.channelId, "invalid start_batch message: we only support batching commit_sig messages")
+              stay()
+            } else if (msg.batchSize > 20) {
+              log.debug("ignoring start_batch with batch_size = {} > 20", msg.batchSize)
+              d.transport ! Warning(msg.channelId, "invalid start_batch message: batch_size must not be greater than 20")
+              stay()
+            } else {
+              log.debug("starting commit_sig batch of size {} for channel_id={}", msg.batchSize, msg.channelId)
+              d.commitSigBatch_opt match {
+                case Some(pending) if pending.received.nonEmpty =>
+                  log.warning("starting batch with incomplete previous batch ({}/{} received)", pending.received.size, pending.batchSize)
+                  // This is a spec violation from our peer: this will likely lead to a force-close.
+                  d.transport ! Warning(msg.channelId, "invalid start_batch message: the previous batch is not done yet")
+                  d.peer ! CommitSigBatch(pending.received)
+                case _ => ()
+              }
+              stay() using d.copy(commitSigBatch_opt = Some(PendingCommitSigBatch(msg.channelId, msg.batchSize, Nil)))
+            }
+          case msg: HasChannelId if d.commitSigBatch_opt.nonEmpty =>
+            // We only support batches of commit_sig messages: other messages will simply be relayed individually.
+            val pending = d.commitSigBatch_opt.get
+            msg match {
+              case msg: CommitSig if msg.channelId == pending.channelId =>
+                val received1 = pending.received :+ msg
+                if (received1.size == pending.batchSize) {
+                  log.debug("received last commit_sig in batch for channel_id={}", msg.channelId)
+                  d.peer ! CommitSigBatch(received1)
+                  stay() using d.copy(commitSigBatch_opt = None)
+                } else {
+                  log.debug("received commit_sig {}/{} in batch for channel_id={}", received1.size, pending.batchSize, msg.channelId)
+                  stay() using d.copy(commitSigBatch_opt = Some(pending.copy(received = received1)))
+                }
+              case _ =>
+                log.warning("received {} as part of a batch: we don't support batching that kind of messages", msg.getClass.getSimpleName)
+                if (pending.received.nonEmpty) d.peer ! CommitSigBatch(pending.received)
+                d.peer ! msg
+                stay() using d.copy(commitSigBatch_opt = None)
+            }
           case msg: CommitSig =>
-            msg.tlvStream.get[CommitSigTlv.BatchTlv].map(_.size) match {
+            // We keep supporting the experimental version of splicing that older Phoenix wallets use.
+            // Once we're confident that enough Phoenix users have upgraded, we should remove this branch.
+            msg.tlvStream.get[CommitSigTlv.ExperimentalBatchTlv].map(_.size) match {
               case Some(batchSize) if batchSize > 25 =>
                 log.warning("received legacy batch of commit_sig exceeding our threshold ({} > 25), processing messages individually", batchSize)
                 // We don't want peers to be able to exhaust our memory by sending batches of dummy messages that we keep in RAM.
@@ -612,6 +658,7 @@ object PeerConnection {
                            gossipTimestampFilter: Option[GossipTimestampFilter] = None,
                            behavior: Behavior = Behavior(),
                            expectedPong_opt: Option[ExpectedPong] = None,
+                           commitSigBatch_opt: Option[PendingCommitSigBatch] = None,
                            legacyCommitSigBatch_opt: Option[PendingCommitSigBatch] = None,
                            isPersistent: Boolean) extends Data with HasTransport
 
diff --git a/eclair-core/src/main/scala/fr/acinq/eclair/wire/protocol/ChannelTlv.scala b/eclair-core/src/main/scala/fr/acinq/eclair/wire/protocol/ChannelTlv.scala
index ac0f921..9aad296 100644
--- a/eclair-core/src/main/scala/fr/acinq/eclair/wire/protocol/ChannelTlv.scala
+++ b/eclair-core/src/main/scala/fr/acinq/eclair/wire/protocol/ChannelTlv.scala
@@ -255,8 +255,16 @@ sealed trait ChannelReestablishTlv extends Tlv
 
 object ChannelReestablishTlv {
 
+  /**
+   * When disconnected in the middle of an interactive-tx session, this field is used to request a retransmission of
+   * [[TxSignatures]] for the given [[txId]].
+   */
   case class NextFundingTlv(txId: TxId) extends ChannelReestablishTlv
+
+  /** The txid of the last [[ChannelReady]] or [[SpliceLocked]] message received before disconnecting, if any. */
   case class YourLastFundingLockedTlv(txId: TxId) extends ChannelReestablishTlv
+
+  /** The txid of our latest outgoing [[ChannelReady]] or [[SpliceLocked]] for this channel. */
   case class MyCurrentFundingLockedTlv(txId: TxId) extends ChannelReestablishTlv
 
   /**
@@ -395,3 +403,13 @@ object ClosingSigTlv {
   )
 }
 
+sealed trait StartBatchTlv extends Tlv
+
+object StartBatchTlv {
+  /** Type of [[LightningMessage]] that is included in the batch, when batching a single message type. */
+  case class MessageType(tag: Int) extends StartBatchTlv
+
+  val startBatchTlvCodec: Codec[TlvStream[StartBatchTlv]] = tlvStream(discriminated[StartBatchTlv].by(varint)
+    .typecase(UInt64(1), tlvField(uint16.as[MessageType]))
+  )
+}
diff --git a/eclair-core/src/main/scala/fr/acinq/eclair/wire/protocol/HtlcTlv.scala b/eclair-core/src/main/scala/fr/acinq/eclair/wire/protocol/HtlcTlv.scala
index e42c216..42a7333 100644
--- a/eclair-core/src/main/scala/fr/acinq/eclair/wire/protocol/HtlcTlv.scala
+++ b/eclair-core/src/main/scala/fr/acinq/eclair/wire/protocol/HtlcTlv.scala
@@ -96,12 +96,23 @@ sealed trait CommitSigTlv extends Tlv
 
 object CommitSigTlv {
 
-  /** @param size the number of [[CommitSig]] messages in the batch */
-  case class BatchTlv(size: Int) extends CommitSigTlv
+  /**
+   * While a splice is ongoing and not locked, we have multiple valid commitments.
+   * We send one [[CommitSig]] message for each valid commitment: this field maps it to the corresponding funding transaction.
+   *
+   * @param txId the funding transaction spent by this commitment.
+   */
+  case class FundingTx(txId: TxId) extends CommitSigTlv
 
-  object BatchTlv {
-    val codec: Codec[BatchTlv] = tlvField(tu16)
-  }
+  private val fundingTxTlv: Codec[FundingTx] = tlvField(txIdAsHash)
+
+  /**
+   * The experimental version of splicing included the number of [[CommitSig]] messages in the batch.
+   * This TLV can be removed once Phoenix users have upgraded to the official version of splicing and use the [[StartBatch]] message.
+   */
+  case class ExperimentalBatchTlv(size: Int) extends CommitSigTlv
+
+  private val experimentalBatchTlv: Codec[ExperimentalBatchTlv] = tlvField(tu16)
 
   /** Partial signature signature for the current commitment transaction, along with the signing nonce used (when using taproot channels). */
   case class PartialSignatureWithNonceTlv(partialSigWithNonce: PartialSignatureWithNonce) extends CommitSigTlv
@@ -111,8 +122,9 @@ object CommitSigTlv {
   }
 
   val commitSigTlvCodec: Codec[TlvStream[CommitSigTlv]] = tlvStream(discriminated[CommitSigTlv].by(varint)
+    .typecase(UInt64(1), fundingTxTlv)
     .typecase(UInt64(2), PartialSignatureWithNonceTlv.codec)
-    .typecase(UInt64(0x47010005), BatchTlv.codec)
+    .typecase(UInt64(0x47010005), experimentalBatchTlv)
   )
 
 }
diff --git a/eclair-core/src/main/scala/fr/acinq/eclair/wire/protocol/LightningMessageCodecs.scala b/eclair-core/src/main/scala/fr/acinq/eclair/wire/protocol/LightningMessageCodecs.scala
index 181268e..f36c6d7 100644
--- a/eclair-core/src/main/scala/fr/acinq/eclair/wire/protocol/LightningMessageCodecs.scala
+++ b/eclair-core/src/main/scala/fr/acinq/eclair/wire/protocol/LightningMessageCodecs.scala
@@ -244,6 +244,11 @@ object LightningMessageCodecs {
       ("lockTime" | uint32) ::
       ("tlvStream" | ClosingSigTlv.closingSigTlvCodec)).as[ClosingSig]
 
+  val startBatchCodec: Codec[StartBatch] = (
+    ("channelId" | bytes32) ::
+      ("batchSize" | uint16) ::
+      ("tlvStream" | StartBatchTlv.startBatchTlvCodec)).as[StartBatch]
+
   val updateAddHtlcCodec: Codec[UpdateAddHtlc] = (
     ("channelId" | bytes32) ::
       ("id" | uint64overflow) ::
@@ -525,6 +530,7 @@ object LightningMessageCodecs {
     .typecase(72, txInitRbfCodec)
     .typecase(73, txAckRbfCodec)
     .typecase(74, txAbortCodec)
+    .typecase(127, startBatchCodec)
     .typecase(128, updateAddHtlcCodec)
     .typecase(130, updateFulfillHtlcCodec)
     .typecase(131, updateFailHtlcCodec)
diff --git a/eclair-core/src/main/scala/fr/acinq/eclair/wire/protocol/LightningMessageTypes.scala b/eclair-core/src/main/scala/fr/acinq/eclair/wire/protocol/LightningMessageTypes.scala
index f4b60cc..0ceb575 100644
--- a/eclair-core/src/main/scala/fr/acinq/eclair/wire/protocol/LightningMessageTypes.scala
+++ b/eclair-core/src/main/scala/fr/acinq/eclair/wire/protocol/LightningMessageTypes.scala
@@ -102,7 +102,10 @@ case class TxAddInput(channelId: ByteVector32,
 
 object TxAddInput {
   def apply(channelId: ByteVector32, serialId: UInt64, sharedInput: OutPoint, sequence: Long): TxAddInput = {
-    TxAddInput(channelId, serialId, None, sharedInput.index, sequence, TlvStream(TxAddInputTlv.SharedInputTxId(sharedInput.txid)))
+    val tlvs = Set[TxAddInputTlv](
+      TxAddInputTlv.SharedInputTxId(sharedInput.txid),
+    )
+    TxAddInput(channelId, serialId, None, sharedInput.index, sequence, TlvStream(tlvs))
   }
 }
 
@@ -146,12 +149,11 @@ case class TxSignatures(channelId: ByteVector32,
 
 object TxSignatures {
   def apply(channelId: ByteVector32, tx: Transaction, witnesses: Seq[ScriptWitness], previousFundingSig_opt: Option[ChannelSpendSignature]): TxSignatures = {
-    val tlvs: Set[TxSignaturesTlv] = Set(
-      previousFundingSig_opt.map {
-        case IndividualSignature(sig) => TxSignaturesTlv.PreviousFundingTxSig(sig)
-        case partialSig: PartialSignatureWithNonce => TxSignaturesTlv.PreviousFundingTxPartialSig(partialSig)
-      }
-    ).flatten
+    val tlvs: Set[TxSignaturesTlv] = previousFundingSig_opt match {
+      case Some(IndividualSignature(sig)) => Set(TxSignaturesTlv.PreviousFundingTxSig(sig))
+      case Some(partialSig: PartialSignatureWithNonce) => Set(TxSignaturesTlv.PreviousFundingTxPartialSig(partialSig))
+      case None => Set.empty
+    }
     TxSignatures(channelId, tx.txid, witnesses, TlvStream(tlvs))
   }
 }
@@ -476,6 +478,15 @@ case class ClosingSig(channelId: ByteVector32, closerScriptPubKey: ByteVector, c
   val nextCloseeNonce_opt: Option[IndividualNonce] = tlvStream.get[ClosingSigTlv.NextCloseeNonce].map(_.nonce)
 }
 
+/** This message is used to indicate that the next [[batchSize]] messages form a single logical message. */
+case class StartBatch(channelId: ByteVector32, batchSize: Int, tlvStream: TlvStream[StartBatchTlv] = TlvStream.empty) extends ChannelMessage with HasChannelId {
+  val messageType_opt: Option[Long] = tlvStream.get[StartBatchTlv.MessageType].map(_.tag)
+}
+
+object StartBatch {
+  def commitSigBatch(channelId: ByteVector32, batchSize: Int): StartBatch = StartBatch(channelId, batchSize, TlvStream(StartBatchTlv.MessageType(132)))
+}
+
 case class UpdateAddHtlc(channelId: ByteVector32,
                          id: Long,
                          amountMsat: MilliSatoshi,
@@ -545,19 +556,21 @@ case class CommitSig(channelId: ByteVector32,
                      signature: IndividualSignature,
                      htlcSignatures: List[ByteVector64],
                      tlvStream: TlvStream[CommitSigTlv] = TlvStream.empty) extends CommitSigs {
+  val fundingTxId_opt: Option[TxId] = tlvStream.get[CommitSigTlv.FundingTx].map(_.txId)
   val partialSignature_opt: Option[PartialSignatureWithNonce] = tlvStream.get[CommitSigTlv.PartialSignatureWithNonceTlv].map(_.partialSigWithNonce)
   val sigOrPartialSig: ChannelSpendSignature = partialSignature_opt.getOrElse(signature)
 }
 
 object CommitSig {
-  def apply(channelId: ByteVector32, signature: ChannelSpendSignature, htlcSignatures: List[ByteVector64], batchSize: Int): CommitSig = {
+  def apply(channelId: ByteVector32, fundingTxId: TxId, signature: ChannelSpendSignature, htlcSignatures: List[ByteVector64], batchSize: Int): CommitSig = {
     val (individualSig, partialSig_opt) = signature match {
       case sig: IndividualSignature => (sig, None)
       case psig: PartialSignatureWithNonce => (IndividualSignature(ByteVector64.Zeroes), Some(psig))
     }
     val tlvs = Set(
-      if (batchSize > 1) Some(CommitSigTlv.BatchTlv(batchSize)) else None,
-      partialSig_opt.map(CommitSigTlv.PartialSignatureWithNonceTlv(_))
+      Some(CommitSigTlv.FundingTx(fundingTxId)),
+      partialSig_opt.map(CommitSigTlv.PartialSignatureWithNonceTlv(_)),
+      if (batchSize > 1) Some(CommitSigTlv.ExperimentalBatchTlv(batchSize)) else None,
     ).flatten[CommitSigTlv]
     CommitSig(channelId, individualSig, htlcSignatures, TlvStream(tlvs))
   }
diff --git a/eclair-core/src/test/scala/fr/acinq/eclair/channel/InteractiveTxBuilderSpec.scala b/eclair-core/src/test/scala/fr/acinq/eclair/channel/InteractiveTxBuilderSpec.scala
index b8d7df7..def27c0 100644
--- a/eclair-core/src/test/scala/fr/acinq/eclair/channel/InteractiveTxBuilderSpec.scala
+++ b/eclair-core/src/test/scala/fr/acinq/eclair/channel/InteractiveTxBuilderSpec.scala
@@ -3030,7 +3030,7 @@ class InteractiveTxBuilderSpec extends TestKitBaseClass with AnyFunSuiteLike wit
     bob ! ReceiveMessage(alice2bob.expectMsgType[SendMessage].msg.asInstanceOf[TxComplete])
     // Alice <-- commit_sig --- Bob
     val successA1 = alice2bob.expectMsgType[Succeeded]
-    val invalidCommitSig = CommitSig(params.channelId, PartialSignatureWithNonce(randomBytes32(), txCompleteBob.commitNonces_opt.get.commitNonce), Nil, batchSize = 1)
+    val invalidCommitSig = CommitSig(params.channelId, successA1.signingSession.fundingTxId, PartialSignatureWithNonce(randomBytes32(), txCompleteBob.commitNonces_opt.get.commitNonce), Nil, batchSize = 1)
     val Left(error) = successA1.signingSession.receiveCommitSig(params.channelParamsA, params.channelKeysA, invalidCommitSig, params.nodeParamsA.currentBlockHeight)(akka.event.NoLogging)
     assert(error.isInstanceOf[InvalidCommitmentSignature])
   }
diff --git a/eclair-core/src/test/scala/fr/acinq/eclair/channel/states/e/NormalSplicesStateSpec.scala b/eclair-core/src/test/scala/fr/acinq/eclair/channel/states/e/NormalSplicesStateSpec.scala
index 17e2aeb..dfab167 100644
--- a/eclair-core/src/test/scala/fr/acinq/eclair/channel/states/e/NormalSplicesStateSpec.scala
+++ b/eclair-core/src/test/scala/fr/acinq/eclair/channel/states/e/NormalSplicesStateSpec.scala
@@ -1650,16 +1650,18 @@ class NormalSplicesStateSpec extends TestKitBaseClass with FixtureAnyFunSuiteLik
     alice ! CMD_SIGN()
     val sigsA = alice2bob.expectMsgType[CommitSigBatch]
     assert(sigsA.batchSize == 2)
+    assert(sigsA.messages.flatMap(_.fundingTxId_opt).toSet == alice.commitments.active.map(_.fundingTxId).toSet)
     alice2bob.forward(bob, sigsA)
     bob2alice.expectMsgType[RevokeAndAck]
     bob2alice.forward(alice)
     val sigsB = bob2alice.expectMsgType[CommitSigBatch]
     assert(sigsB.batchSize == 2)
+    assert(sigsB.messages.flatMap(_.fundingTxId_opt).toSet == alice.commitments.active.map(_.fundingTxId).toSet)
     bob2alice.forward(alice, sigsB)
     alice2bob.expectMsgType[RevokeAndAck]
     alice2bob.forward(bob)
-    awaitCond(alice.stateData.asInstanceOf[DATA_NORMAL].commitments.active.forall(_.localCommit.spec.htlcs.size == 1))
-    awaitCond(bob.stateData.asInstanceOf[DATA_NORMAL].commitments.active.forall(_.localCommit.spec.htlcs.size == 1))
+    awaitCond(alice.commitments.active.forall(_.localCommit.spec.htlcs.size == 1))
+    awaitCond(bob.commitments.active.forall(_.localCommit.spec.htlcs.size == 1))
   }
 
   test("recv CMD_ADD_HTLC with multiple commitments (missing nonces)", Tag(ChannelStateTestsTags.OptionSimpleTaproot)) { f =>
@@ -1707,11 +1709,13 @@ class NormalSplicesStateSpec extends TestKitBaseClass with FixtureAnyFunSuiteLik
     alice2bob.forward(bob)
     val sigsA = alice2bob.expectMsgType[CommitSigBatch]
     assert(sigsA.batchSize == 2)
+    assert(sigsA.messages.flatMap(_.fundingTxId_opt).toSet == alice.commitments.active.map(_.fundingTxId).toSet)
     alice2bob.forward(bob, sigsA)
     assert(bob2alice.expectMsgType[RevokeAndAck].nextCommitNonces.size == 2)
     bob2alice.forward(alice)
     val sigsB = bob2alice.expectMsgType[CommitSigBatch]
     assert(sigsB.batchSize == 2)
+    assert(sigsB.messages.flatMap(_.fundingTxId_opt).toSet == alice.commitments.active.map(_.fundingTxId).toSet)
     bob2alice.forward(alice, sigsB)
     assert(alice2bob.expectMsgType[RevokeAndAck].nextCommitNonces.size == 2)
     alice2bob.forward(bob)
@@ -1840,7 +1844,7 @@ class NormalSplicesStateSpec extends TestKitBaseClass with FixtureAnyFunSuiteLik
     alice2bob.forward(bob, commitSigsAlice)
     bob2alice.expectMsgType[RevokeAndAck]
     bob2alice.forward(alice)
-    bob2alice.expectMsgType[CommitSig]
+    assert(bob2alice.expectMsgType[CommitSig].fundingTxId_opt.contains(spliceTx2.txid))
     bob2alice.forward(alice)
     alice2bob.expectMsgType[RevokeAndAck]
     alice2bob.forward(bob)
@@ -1944,10 +1948,12 @@ class NormalSplicesStateSpec extends TestKitBaseClass with FixtureAnyFunSuiteLik
     val bobCommitIndex = bob.stateData.asInstanceOf[DATA_NORMAL].commitments.localCommitIndex
 
     val sender = initiateSpliceWithoutSigs(f, spliceIn_opt = Some(SpliceIn(500_000 sat)), spliceOut_opt = Some(SpliceOut(100_000 sat, defaultSpliceOutScriptPubKey)))
-    alice2bob.expectMsgType[CommitSig] // Bob doesn't receive Alice's commit_sig
-    bob2alice.expectMsgType[CommitSig] // Alice doesn't receive Bob's commit_sig
+    val commitSigA = alice2bob.expectMsgType[CommitSig] // Bob doesn't receive Alice's commit_sig
+    val commitSigB = bob2alice.expectMsgType[CommitSig] // Alice doesn't receive Bob's commit_sig
     awaitCond(alice.stateData.asInstanceOf[DATA_NORMAL].spliceStatus.isInstanceOf[SpliceStatus.SpliceWaitingForSigs])
     val spliceStatus = alice.stateData.asInstanceOf[DATA_NORMAL].spliceStatus.asInstanceOf[SpliceStatus.SpliceWaitingForSigs]
+    assert(commitSigA.fundingTxId_opt.contains(spliceStatus.signingSession.fundingTx.txId))
+    assert(commitSigB.fundingTxId_opt.contains(spliceStatus.signingSession.fundingTx.txId))
 
     disconnect(f)
 
@@ -1960,7 +1966,7 @@ class NormalSplicesStateSpec extends TestKitBaseClass with FixtureAnyFunSuiteLik
     alice2bob.forward(bob, channelReestablishAlice1)
     bob2alice.forward(alice, channelReestablishBob1.copy(nextLocalCommitmentNumber = bobCommitIndex + 1))
     // In that case Alice won't retransmit commit_sig and the splice won't complete since they haven't exchanged tx_signatures.
-    bob2alice.expectMsgType[CommitSig]
+    assert(bob2alice.expectMsgType[CommitSig].fundingTxId_opt.contains(spliceStatus.signingSession.fundingTx.txId))
     bob2alice.forward(alice)
     alice2bob.expectNoMessage(100 millis)
     assert(alice.stateData.asInstanceOf[DATA_NORMAL].spliceStatus.isInstanceOf[SpliceStatus.SpliceWaitingForSigs])
@@ -1981,7 +1987,7 @@ class NormalSplicesStateSpec extends TestKitBaseClass with FixtureAnyFunSuiteLik
     assert(channelReestablishBob2.nextLocalCommitmentNumber == bobCommitIndex)
 
     // Alice retransmits commit_sig and both retransmit tx_signatures.
-    alice2bob.expectMsgType[CommitSig]
+    assert(alice2bob.expectMsgType[CommitSig].fundingTxId_opt.contains(spliceStatus.signingSession.fundingTx.txId))
     alice2bob.forward(bob)
     bob2alice.expectMsgType[TxSignatures]
     bob2alice.forward(alice)
@@ -1990,6 +1996,7 @@ class NormalSplicesStateSpec extends TestKitBaseClass with FixtureAnyFunSuiteLik
     sender.expectMsgType[RES_SPLICE]
 
     val spliceTx = alice.stateData.asInstanceOf[DATA_NORMAL].commitments.latest.localFundingStatus.signedTx_opt.get
+    assert(spliceTx.txid == spliceStatus.signingSession.fundingTx.txId)
     alice2blockchain.expectWatchFundingConfirmed(spliceTx.txid)
     bob2blockchain.expectWatchFundingConfirmed(spliceTx.txid)
     alice ! WatchFundingConfirmedTriggered(BlockHeight(42), 0, spliceTx)
@@ -2854,11 +2861,14 @@ class NormalSplicesStateSpec extends TestKitBaseClass with FixtureAnyFunSuiteLik
     alice2bob.expectMsgType[TxSignatures] // Bob doesn't receive Alice's tx_signatures
 
     awaitCond(alice.stateData.asInstanceOf[DATA_NORMAL].spliceStatus == SpliceStatus.NoSplice)
+    val fundingTxIds = alice.commitments.active.map(_.fundingTxId).toSet
+    assert(fundingTxIds.size == 2)
     val (_, cmd) = makeCmdAdd(25_000_000 msat, bob.nodeParams.nodeId, bob.nodeParams.currentBlockHeight)
     alice ! cmd.copy(commit = true)
     alice2bob.expectMsgType[UpdateAddHtlc] // Bob doesn't receive Alice's update_add_htlc
     inside(alice2bob.expectMsgType[CommitSigBatch]) { batch => // Bob doesn't receive Alice's commit_sigs
       assert(batch.batchSize == 2)
+      assert(batch.messages.flatMap(_.fundingTxId_opt).toSet == fundingTxIds)
     }
     alice2bob.expectNoMessage(100 millis)
     bob2alice.expectNoMessage(100 millis)
@@ -2874,12 +2884,14 @@ class NormalSplicesStateSpec extends TestKitBaseClass with FixtureAnyFunSuiteLik
     alice2bob.forward(bob)
     inside(alice2bob.expectMsgType[CommitSigBatch]) { batch =>
       assert(batch.batchSize == 2)
+      assert(batch.messages.flatMap(_.fundingTxId_opt).toSet == fundingTxIds)
       alice2bob.forward(bob)
     }
     bob2alice.expectMsgType[RevokeAndAck]
     bob2alice.forward(alice)
     inside(bob2alice.expectMsgType[CommitSigBatch]) { batch =>
       assert(batch.batchSize == 2)
+      assert(batch.messages.flatMap(_.fundingTxId_opt).toSet == fundingTxIds)
       bob2alice.forward(alice)
     }
     alice2bob.expectMsgType[RevokeAndAck]
@@ -2932,12 +2944,12 @@ class NormalSplicesStateSpec extends TestKitBaseClass with FixtureAnyFunSuiteLik
     val sender = TestProbe()
     alice ! CMD_SIGN(Some(sender.ref))
     sender.expectMsgType[RES_SUCCESS[CMD_SIGN]]
-    alice2bob.expectMsgType[CommitSig]
+    assert(alice2bob.expectMsgType[CommitSig].fundingTxId_opt.contains(fundingTx.txid))
     alice2bob.forward(bob)
     bob2alice.forward(alice, bobSpliceLocked)
     bob2alice.expectMsgType[RevokeAndAck]
     bob2alice.forward(alice)
-    bob2alice.expectMsgType[CommitSig]
+    assert(bob2alice.expectMsgType[CommitSig].fundingTxId_opt.contains(fundingTx.txid))
     bob2alice.forward(alice)
     alice2bob.expectMsgType[RevokeAndAck]
     alice2bob.forward(bob)
@@ -2992,7 +3004,7 @@ class NormalSplicesStateSpec extends TestKitBaseClass with FixtureAnyFunSuiteLik
     assert(bob.commitments.active.size == 1)
     alice2bob.expectMsgType[UpdateAddHtlc]
     alice2bob.forward(bob)
-    assert(alice2bob.expectMsgType[CommitSig].tlvStream.get[CommitSigTlv.BatchTlv].isEmpty)
+    assert(alice2bob.expectMsgType[CommitSig].tlvStream.get[CommitSigTlv.ExperimentalBatchTlv].isEmpty)
     alice2bob.forward(bob)
     bob2alice.expectMsgType[RevokeAndAck]
     bob2alice.forward(alice)
diff --git a/eclair-core/src/test/scala/fr/acinq/eclair/io/PeerConnectionSpec.scala b/eclair-core/src/test/scala/fr/acinq/eclair/io/PeerConnectionSpec.scala
index c6d6451..a9aa317 100644
--- a/eclair-core/src/test/scala/fr/acinq/eclair/io/PeerConnectionSpec.scala
+++ b/eclair-core/src/test/scala/fr/acinq/eclair/io/PeerConnectionSpec.scala
@@ -346,6 +346,8 @@ class PeerConnectionSpec extends TestKitBaseClass with FixtureAnyFunSuiteLike wi
       CommitSig(channelId, IndividualSignature(randomBytes64()), Nil),
     )
     probe.send(peerConnection, CommitSigBatch(commitSigs))
+    // We insert a start_batch message.
+    transport.expectMsg(StartBatch(channelId, batchSize = 3, TlvStream(StartBatchTlv.MessageType(132))))
     commitSigs.foreach(commitSig => transport.expectMsg(commitSig))
     transport.expectNoMessage(100 millis)
   }
@@ -357,8 +359,8 @@ class PeerConnectionSpec extends TestKitBaseClass with FixtureAnyFunSuiteLike wi
     // We receive a batch of commit_sig messages from a first channel.
     val channelId1 = randomBytes32()
     val commitSigs1 = Seq(
-      CommitSig(channelId1, IndividualSignature(randomBytes64()), Nil, batchSize = 2),
-      CommitSig(channelId1, IndividualSignature(randomBytes64()), Nil, batchSize = 2),
+      CommitSig(channelId1, IndividualSignature(randomBytes64()), Nil, TlvStream(CommitSigTlv.ExperimentalBatchTlv(2))),
+      CommitSig(channelId1, IndividualSignature(randomBytes64()), Nil, TlvStream(CommitSigTlv.ExperimentalBatchTlv(2))),
     )
     transport.send(peerConnection, commitSigs1.head)
     transport.expectMsg(TransportHandler.ReadAck(commitSigs1.head))
@@ -370,9 +372,9 @@ class PeerConnectionSpec extends TestKitBaseClass with FixtureAnyFunSuiteLike wi
     // We receive a batch of commit_sig messages from a second channel.
     val channelId2 = randomBytes32()
     val commitSigs2 = Seq(
-      CommitSig(channelId2, IndividualSignature(randomBytes64()), Nil, batchSize = 3),
-      CommitSig(channelId2, IndividualSignature(randomBytes64()), Nil, batchSize = 3),
-      CommitSig(channelId2, IndividualSignature(randomBytes64()), Nil, batchSize = 3),
+      CommitSig(channelId2, IndividualSignature(randomBytes64()), Nil, TlvStream(CommitSigTlv.ExperimentalBatchTlv(3))),
+      CommitSig(channelId2, IndividualSignature(randomBytes64()), Nil, TlvStream(CommitSigTlv.ExperimentalBatchTlv(3))),
+      CommitSig(channelId2, IndividualSignature(randomBytes64()), Nil, TlvStream(CommitSigTlv.ExperimentalBatchTlv(3))),
     )
     commitSigs2.dropRight(1).foreach(commitSig => {
       transport.send(peerConnection, commitSig)
@@ -385,8 +387,8 @@ class PeerConnectionSpec extends TestKitBaseClass with FixtureAnyFunSuiteLike wi
 
     // We receive another batch of commit_sig messages from the first channel, with unrelated messages in the batch.
     val commitSigs3 = Seq(
-      CommitSig(channelId1, IndividualSignature(randomBytes64()), Nil, batchSize = 2),
-      CommitSig(channelId1, IndividualSignature(randomBytes64()), Nil, batchSize = 2),
+      CommitSig(channelId1, IndividualSignature(randomBytes64()), Nil, TlvStream(CommitSigTlv.ExperimentalBatchTlv(2))),
+      CommitSig(channelId1, IndividualSignature(randomBytes64()), Nil, TlvStream(CommitSigTlv.ExperimentalBatchTlv(2))),
     )
     transport.send(peerConnection, commitSigs3.head)
     transport.expectMsg(TransportHandler.ReadAck(commitSigs3.head))
@@ -406,9 +408,9 @@ class PeerConnectionSpec extends TestKitBaseClass with FixtureAnyFunSuiteLike wi
     // We start receiving a batch of commit_sig messages from the first channel, interleaved with a batch from the second
     // channel, which is not supported.
     val commitSigs4 = Seq(
-      CommitSig(channelId1, IndividualSignature(randomBytes64()), Nil, batchSize = 2),
-      CommitSig(channelId2, IndividualSignature(randomBytes64()), Nil, batchSize = 2),
-      CommitSig(channelId2, IndividualSignature(randomBytes64()), Nil, batchSize = 2),
+      CommitSig(channelId1, IndividualSignature(randomBytes64()), Nil, TlvStream(CommitSigTlv.ExperimentalBatchTlv(2))),
+      CommitSig(channelId2, IndividualSignature(randomBytes64()), Nil, TlvStream(CommitSigTlv.ExperimentalBatchTlv(2))),
+      CommitSig(channelId2, IndividualSignature(randomBytes64()), Nil, TlvStream(CommitSigTlv.ExperimentalBatchTlv(2))),
     )
     transport.send(peerConnection, commitSigs4.head)
     transport.expectMsg(TransportHandler.ReadAck(commitSigs4.head))
@@ -421,7 +423,7 @@ class PeerConnectionSpec extends TestKitBaseClass with FixtureAnyFunSuiteLike wi
     peer.expectMsg(CommitSigBatch(commitSigs4.tail))
 
     // We receive a batch that exceeds our threshold: we process them individually.
-    val invalidCommitSigs = (0 until 30).map(_ => CommitSig(channelId2, IndividualSignature(randomBytes64()), Nil, batchSize = 30))
+    val invalidCommitSigs = (0 until 30).map(_ => CommitSig(channelId2, IndividualSignature(randomBytes64()), Nil, TlvStream(CommitSigTlv.ExperimentalBatchTlv(30))))
     invalidCommitSigs.foreach(commitSig => {
       transport.send(peerConnection, commitSig)
       transport.expectMsg(TransportHandler.ReadAck(commitSig))
@@ -429,6 +431,135 @@ class PeerConnectionSpec extends TestKitBaseClass with FixtureAnyFunSuiteLike wi
     })
   }
 
+  test("receive batch of commit_sig messages") { f =>
+    import f._
+    connect(nodeParams, remoteNodeId, switchboard, router, connection, transport, peerConnection, peer)
+
+    // A first channel has a pending splice.
+    val channelId1 = randomBytes32()
+    val startBatch1 = StartBatch(channelId1, batchSize = 2, TlvStream(StartBatchTlv.MessageType(132)))
+    val commitSigs1 = Seq(
+      CommitSig(channelId1, IndividualSignature(randomBytes64()), Nil, TlvStream(CommitSigTlv.FundingTx(randomTxId()))),
+      CommitSig(channelId1, IndividualSignature(randomBytes64()), Nil, TlvStream(CommitSigTlv.FundingTx(randomTxId()))),
+    )
+    transport.send(peerConnection, startBatch1)
+    transport.expectMsg(TransportHandler.ReadAck(startBatch1))
+    transport.send(peerConnection, commitSigs1(0))
+    transport.expectMsg(TransportHandler.ReadAck(commitSigs1(0)))
+    peer.expectNoMessage(100 millis)
+    transport.send(peerConnection, commitSigs1(1))
+    transport.expectMsg(TransportHandler.ReadAck(commitSigs1(1)))
+    peer.expectMsg(CommitSigBatch(commitSigs1))
+
+    // Another channel has 2 pending splices.
+    val channelId2 = randomBytes32()
+    val startBatch2 = StartBatch(channelId2, batchSize = 3, TlvStream(StartBatchTlv.MessageType(132)))
+    val commitSigs2 = Seq(
+      CommitSig(channelId2, IndividualSignature(randomBytes64()), Nil, TlvStream(CommitSigTlv.FundingTx(randomTxId()))),
+      CommitSig(channelId2, IndividualSignature(randomBytes64()), Nil, TlvStream(CommitSigTlv.FundingTx(randomTxId()))),
+      CommitSig(channelId2, IndividualSignature(randomBytes64()), Nil, TlvStream(CommitSigTlv.FundingTx(randomTxId()))),
+    )
+    transport.send(peerConnection, startBatch2)
+    transport.expectMsg(TransportHandler.ReadAck(startBatch2))
+    transport.send(peerConnection, commitSigs2(0))
+    transport.expectMsg(TransportHandler.ReadAck(commitSigs2(0)))
+    transport.send(peerConnection, commitSigs2(1))
+    transport.expectMsg(TransportHandler.ReadAck(commitSigs2(1)))
+    peer.expectNoMessage(100 millis)
+    transport.send(peerConnection, commitSigs2(2))
+    transport.expectMsg(TransportHandler.ReadAck(commitSigs2(2)))
+    peer.expectMsg(CommitSigBatch(commitSigs2))
+
+    // We receive another batch of commit_sig messages for the first channel.
+    val startBatch3 = StartBatch(channelId1, batchSize = 3, TlvStream(StartBatchTlv.MessageType(132)))
+    val commitSigs3 = Seq(
+      CommitSig(channelId1, IndividualSignature(randomBytes64()), Nil, TlvStream(CommitSigTlv.FundingTx(randomTxId()))),
+      CommitSig(channelId1, IndividualSignature(randomBytes64()), Nil, TlvStream(CommitSigTlv.FundingTx(randomTxId()))),
+      CommitSig(channelId1, IndividualSignature(randomBytes64()), Nil, TlvStream(CommitSigTlv.FundingTx(randomTxId()))),
+    )
+    transport.send(peerConnection, startBatch3)
+    transport.expectMsg(TransportHandler.ReadAck(startBatch3))
+    transport.send(peerConnection, commitSigs3(0))
+    transport.expectMsg(TransportHandler.ReadAck(commitSigs3(0)))
+    transport.send(peerConnection, commitSigs3(1))
+    transport.expectMsg(TransportHandler.ReadAck(commitSigs3(1)))
+    peer.expectNoMessage(100 millis)
+    transport.send(peerConnection, commitSigs3(2))
+    transport.expectMsg(TransportHandler.ReadAck(commitSigs3(2)))
+    peer.expectMsg(CommitSigBatch(commitSigs3))
+
+    // We reject batches that mix unrelated channels.
+    val startBatch4 = StartBatch(channelId1, batchSize = 3, TlvStream(StartBatchTlv.MessageType(132)))
+    val commitSigs4 = Seq(
+      CommitSig(channelId1, IndividualSignature(randomBytes64()), Nil, TlvStream(CommitSigTlv.FundingTx(randomTxId()))),
+      CommitSig(channelId2, IndividualSignature(randomBytes64()), Nil, TlvStream(CommitSigTlv.FundingTx(randomTxId()))),
+      CommitSig(channelId2, IndividualSignature(randomBytes64()), Nil, TlvStream(CommitSigTlv.FundingTx(randomTxId()))),
+    )
+    transport.send(peerConnection, startBatch4)
+    transport.expectMsg(TransportHandler.ReadAck(startBatch4))
+    transport.send(peerConnection, commitSigs4(0))
+    transport.expectMsg(TransportHandler.ReadAck(commitSigs4(0)))
+    peer.expectNoMessage(100 millis)
+    transport.send(peerConnection, commitSigs4(1))
+    transport.expectMsg(TransportHandler.ReadAck(commitSigs4(1)))
+    peer.expectMsg(CommitSigBatch(commitSigs4.take(1)))
+    peer.expectMsg(commitSigs4(1))
+    peer.expectNoMessage(100 millis)
+    transport.send(peerConnection, commitSigs4(2))
+    transport.expectMsg(TransportHandler.ReadAck(commitSigs4(2)))
+    peer.expectMsg(commitSigs4(2))
+    peer.expectNoMessage(100 millis)
+  }
+
+  test("receive unsupported batch of channel messages") { f =>
+    import f._
+    connect(nodeParams, remoteNodeId, switchboard, router, connection, transport, peerConnection, peer)
+
+    // We receive a batch of splice_locked messages: we forward them individually.
+    val channelId = randomBytes32()
+    val startBatch1 = StartBatch(channelId, batchSize = 2) // note that start_batch doesn't indicate the message type
+    val spliceLocked1 = SpliceLocked(channelId, randomTxId())
+    val spliceLocked2 = SpliceLocked(channelId, randomTxId())
+    transport.send(peerConnection, startBatch1)
+    transport.expectMsg(TransportHandler.ReadAck(startBatch1))
+    transport.expectMsgType[Warning]
+    transport.send(peerConnection, spliceLocked1)
+    transport.expectMsg(TransportHandler.ReadAck(spliceLocked1))
+    peer.expectMsg(spliceLocked1)
+    transport.send(peerConnection, spliceLocked2)
+    transport.expectMsg(TransportHandler.ReadAck(spliceLocked2))
+    peer.expectMsg(spliceLocked2)
+
+    // We receive a batch containing commit_sig and an unrelated message.
+    val startBatch2 = StartBatch(channelId, batchSize = 3, TlvStream(StartBatchTlv.MessageType(132)))
+    val commitSig1 = CommitSig(channelId, IndividualSignature(randomBytes64()), Nil, TlvStream(CommitSigTlv.FundingTx(randomTxId())))
+    val commitSig2 = CommitSig(channelId, IndividualSignature(randomBytes64()), Nil, TlvStream(CommitSigTlv.FundingTx(randomTxId())))
+    val spliceLocked3 = SpliceLocked(channelId, randomTxId())
+    transport.send(peerConnection, startBatch2)
+    transport.expectMsg(TransportHandler.ReadAck(startBatch2))
+    transport.send(peerConnection, commitSig1)
+    transport.expectMsg(TransportHandler.ReadAck(commitSig1))
+    transport.send(peerConnection, commitSig2)
+    transport.expectMsg(TransportHandler.ReadAck(commitSig2))
+    peer.expectNoMessage(100 millis)
+    transport.send(peerConnection, spliceLocked3)
+    transport.expectMsg(TransportHandler.ReadAck(spliceLocked3))
+    peer.expectMsg(CommitSigBatch(commitSig1 :: commitSig2 :: Nil))
+    peer.expectMsg(spliceLocked3)
+    peer.expectNoMessage(100 millis)
+
+    // We receive a batch exceeding 20 elements: we relay messages individually.
+    val startBatch3 = StartBatch(channelId, batchSize = 21, TlvStream(StartBatchTlv.MessageType(132)))
+    val commitSig3 = CommitSig(channelId, IndividualSignature(randomBytes64()), Nil, TlvStream(CommitSigTlv.FundingTx(randomTxId())))
+    transport.send(peerConnection, startBatch3)
+    transport.expectMsg(TransportHandler.ReadAck(startBatch3))
+    transport.expectMsgType[Warning]
+    transport.send(peerConnection, commitSig3)
+    transport.expectMsg(TransportHandler.ReadAck(commitSig3))
+    peer.expectMsg(commitSig3)
+    peer.expectNoMessage(100 millis)
+  }
+
   test("react to peer's bad behavior") { f =>
     import f._
     val probe = TestProbe()
diff --git a/eclair-core/src/test/scala/fr/acinq/eclair/wire/protocol/LightningMessageCodecsSpec.scala b/eclair-core/src/test/scala/fr/acinq/eclair/wire/protocol/LightningMessageCodecsSpec.scala
index baaaf8c..88ed2d1 100644
--- a/eclair-core/src/test/scala/fr/acinq/eclair/wire/protocol/LightningMessageCodecsSpec.scala
+++ b/eclair-core/src/test/scala/fr/acinq/eclair/wire/protocol/LightningMessageCodecsSpec.scala
@@ -168,7 +168,7 @@ class LightningMessageCodecsSpec extends AnyFunSuite {
       hex"0088" ++ channelId ++ hex"0001020304050607 0809aabbccddeeff" ++ key.value ++ point.value ++ hex"fe47010000 07 bbbbbbbbbbbbbb" -> ChannelReestablish(channelId, 0x01020304050607L, 0x0809aabbccddeeffL, key, point, TlvStream[ChannelReestablishTlv](Set.empty[ChannelReestablishTlv], Set(GenericTlv(tlvTag, hex"bbbbbbbbbbbbbb")))),
 
       hex"0084" ++ channelId ++ signature ++ hex"0000" -> CommitSig(channelId, IndividualSignature(signature), Nil),
-      hex"0084" ++ channelId ++ ByteVector64.Zeroes ++ hex"0000" ++ hex"02 62" ++ partialSig ++ nonce.data -> CommitSig(channelId, PartialSignatureWithNonce(partialSig, nonce), Nil, batchSize = 1),
+      hex"0084" ++ channelId ++ ByteVector64.Zeroes ++ hex"0000" ++ hex"01 20" ++ txId.value.reverse ++ hex"02 62" ++ partialSig ++ nonce.data -> CommitSig(channelId, txId, PartialSignatureWithNonce(partialSig, nonce), Nil, batchSize = 1),
       hex"0084" ++ channelId ++ signature ++ hex"0000 fe47010000 00" -> CommitSig(channelId, IndividualSignature(signature), Nil, TlvStream[CommitSigTlv](Set.empty[CommitSigTlv], Set(GenericTlv(tlvTag, ByteVector.empty)))),
       hex"0084" ++ channelId ++ signature ++ hex"0000 fe47010000 07 cccccccccccccc" -> CommitSig(channelId, IndividualSignature(signature), Nil, TlvStream[CommitSigTlv](Set.empty[CommitSigTlv], Set(GenericTlv(tlvTag, hex"cccccccccccccc")))),
 
@@ -441,6 +441,23 @@ class LightningMessageCodecsSpec extends AnyFunSuite {
     }
   }
 
+  test("encode/decode start_batch message") {
+    val channelId = ByteVector32(hex"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa")
+    val testCases = Seq(
+      StartBatch(channelId, 1) -> hex"007f aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa 0001",
+      StartBatch(channelId, 7) -> hex"007f aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa 0007",
+      StartBatch.commitSigBatch(channelId, 7) -> hex"007f aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa 0007 01020084",
+      StartBatch(channelId, 7, TlvStream(StartBatchTlv.MessageType(57331))) -> hex"007f aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa 0007 0102dff3",
+      StartBatch(channelId, 32000) -> hex"007f aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa 7d00",
+    )
+    testCases.foreach { case (msg, bin) =>
+      val decoded = lightningMessageCodec.decode(bin.bits).require.value
+      assert(decoded == msg)
+      val encoded = lightningMessageCodec.encode(msg).require.bytes
+      assert(encoded == bin)
+    }
+  }
+
   test("encode/decode closing_signed") {
     val defaultSig = ByteVector64(hex"01010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101")
     val testCases = Seq(
@@ -696,9 +713,9 @@ class LightningMessageCodecsSpec extends AnyFunSuite {
   test("encode/decode commit_sig batch") {
     val channelId = randomBytes32()
     val batch = CommitSigBatch(Seq(
-      CommitSig(channelId, ChannelSpendSignature.IndividualSignature(randomBytes64()), Nil, batchSize = 3),
-      CommitSig(channelId, ChannelSpendSignature.IndividualSignature(randomBytes64()), Nil, batchSize = 3),
-      CommitSig(channelId, ChannelSpendSignature.IndividualSignature(randomBytes64()), Nil, batchSize = 3),
+      CommitSig(channelId, randomTxId(), ChannelSpendSignature.IndividualSignature(randomBytes64()), Nil, batchSize = 3),
+      CommitSig(channelId, randomTxId(), ChannelSpendSignature.IndividualSignature(randomBytes64()), Nil, batchSize = 3),
+      CommitSig(channelId, randomTxId(), ChannelSpendSignature.IndividualSignature(randomBytes64()), Nil, batchSize = 3),
     ))
     val encoded = lightningMessageCodec.encode(batch).require
     val decoded = lightningMessageCodec.decode(encoded).require.value