Use new NoopAddHtlc TLV when sending assets with default above-dust anchor amt

rfqmsg/aux_features.go

@@ -0,0 +1,9 @@
+//go:build !dev
+
+package rfqmsg
+
+var (
+	// UseNoOpHTLCs is set to false, as we don't want to enable it for
+	// production builds.
+	UseNoOpHTLCs = false
+)

rfqmsg/aux_features_dev.go

@@ -0,0 +1,8 @@
+//go:build dev
+
+package rfqmsg
+
+var (
+	// UseNoOpHTLCs is set to true, as we want to enable it for dev builds.
+	UseNoOpHTLCs = true
+)

rfqmsg/records.go

@@ -12,6 +12,7 @@ import (
 	"github.com/lightninglabs/taproot-assets/asset"
 	"github.com/lightninglabs/taproot-assets/fn"
 	"github.com/lightninglabs/taproot-assets/rfqmath"
+	"github.com/lightningnetwork/lnd/lnwallet"
 	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/lightningnetwork/lnd/tlv"
 )
@@ -59,6 +60,13 @@ type Htlc struct {
 
 	// RfqID is the RFQ ID that corresponds to the HTLC.
 	RfqID tlv.OptionalRecordT[HtlcRfqIDType, ID]
+
+	// NoopAdd is a flag that indicates whether this HTLC should be marked
+	// as a noop_add for LND. A noop_add HTLC behaves identically to a
+	// normal HTLC except for the settlement step, where the satoshi amount
+	// is returned back to the sender, but the commitment blob is still
+	// updated to reflect the asset balance changes.
+	NoopAdd bool
 }
 
 // NewHtlc creates a new Htlc record with the given funded assets.
@@ -135,9 +143,19 @@ func (h *Htlc) Records() []tlv.Record {
 		records = append(records, r.Record())
 	})
 
+	if h.NoopAdd {
+		r := tlv.NewPrimitiveRecord[lnwallet.NoopAddHtlcType](true)
+		records = append(records, r.Record())
+	}
+
 	return records
 }
 
+// SetNoopAdd flags the HTLC as a noop_add.
+func (h *Htlc) SetNoopAdd(noopActive bool) {
+	h.NoopAdd = noopActive
+}
+
 // Encode serializes the Htlc to the given io.Writer.
 func (h *Htlc) Encode(w io.Writer) error {
 	tlvRecords := h.Records()