Delay HTLC txs in 0FC channels until both commit and anchor txs confirm

It is possible to claim HTLCs and the P2A anchor in the same
transaction, but we leave aggregating these claims to a follow-up.

For now, we imitate the behavior of CSV anchor channels, and wait for
the commitment transaction to confirm before broadcasting HTLC
transactions.

Co-authored-by: Matt Corallo <[email protected]>

Author: tankyleo

lightning/src/chain/channelmonitor.rs

@@ -3950,10 +3950,18 @@ impl<Signer: EcdsaChannelSigner> ChannelMonitorImpl<Signer> {
 		// new channel updates.
 		self.holder_tx_signed = true;
 		let mut watch_outputs = Vec::new();
-		// We can't broadcast our HTLC transactions while the commitment transaction is
-		// unconfirmed. We'll delay doing so until we detect the confirmed commitment in
-		// `transactions_confirmed`.
-		if !funding.channel_type_features().supports_anchors_zero_fee_htlc_tx() {
+		// In CSV anchor channels, we can't broadcast our HTLC transactions while the commitment transaction is
+		// unconfirmed.
+		// We'll delay doing so until we detect the confirmed commitment in `transactions_confirmed`.
+		//
+		// TODO: For now in 0FC channels, we also delay broadcasting any HTLC transactions until the commitment
+		// transaction gets confirmed. It is nonetheless possible to add HTLC spends to the P2A spend
+		// transaction while the commitment transaction is still unconfirmed.
+		let zero_fee_htlcs =
+			self.channel_type_features().supports_anchors_zero_fee_htlc_tx();
+		let zero_fee_commitments =
+			self.channel_type_features().supports_anchor_zero_fee_commitments();
+		if !zero_fee_htlcs && !zero_fee_commitments {
 			// Because we're broadcasting a commitment transaction, we should construct the package
 			// assuming it gets confirmed in the next block. Sadly, we have code which considers
 			// "not yet confirmed" things as discardable, so we cannot do that here.