htlcswitch: relay experimental endorsement signal with update_add_htlc

itest/lnd_forward_interceptor_test.go

@@ -530,9 +530,10 @@ func testForwardInterceptorWireRecords(ht *lntest.HarnessTest) {
 	require.NoError(ht, err, "failed to send request")
 
 	// Assert that the Alice -> Bob custom records in update_add_htlc are
-	// not propagated on the Bob -> Carol link.
+	// not propagated on the Bob -> Carol link, just an endorsement signal.
 	packet = ht.ReceiveHtlcInterceptor(carolInterceptor)
-	require.Len(ht, packet.InWireCustomRecords, 0)
+	require.Equal(ht, lntest.CustomRecordsWithUnendorsed(nil),
+		packet.InWireCustomRecords)
 
 	// We're going to tell Carol to forward 5k sats less to Dave. We need to
 	// set custom records on the HTLC as well, to make sure the HTLC isn't

itest/lnd_invoice_acceptor_test.go

@@ -102,9 +102,12 @@ func testInvoiceHtlcModifierBasic(ht *lntest.HarnessTest) {
 		require.EqualValues(
 			ht, tc.sendAmountMsat, modifierRequest.ExitHtlcAmt,
 		)
+
+		// Expect custom records plus endorsement signal.
 		require.Equal(
-			ht, tc.lastHopCustomRecords,
-			modifierRequest.ExitHtlcWireCustomRecords,
+			ht, lntest.CustomRecordsWithUnendorsed(
+				tc.lastHopCustomRecords,
+			), modifierRequest.ExitHtlcWireCustomRecords,
 		)
 
 		// For all other packets we resolve according to the test case.
@@ -140,8 +143,9 @@ func testInvoiceHtlcModifierBasic(ht *lntest.HarnessTest) {
 
 		require.Len(ht, updatedInvoice.Htlcs, 1)
 		require.Equal(
-			ht, tc.lastHopCustomRecords,
-			updatedInvoice.Htlcs[0].CustomRecords,
+			ht, lntest.CustomRecordsWithUnendorsed(
+				tc.lastHopCustomRecords,
+			), updatedInvoice.Htlcs[0].CustomRecords,
 		)
 
 		// Make sure the custom channel data contains the encoded