sdk/swaps: Reject channel receive type in pay quotes

Ark-channel settlement identifies a completed receive and is not a valid
pay-side swap quote. Reject it explicitly in preview and execution
validation so every settlement enum has deliberate semantics.

Author: sputn1ck

sdk/swaps/in_swap_quote.go

@@ -164,6 +164,10 @@ func validateInSwapPreview(invoice string, quote *InSwapQuote,
 	expectedAmountSat := expectedInvoiceSat + quote.FeeSat
 	switch quote.SettlementType {
 	case "", SettlementTypeLightning, SettlementTypeInArk:
+	case SettlementTypeArkChannel:
+		return fmt.Errorf("ark channel settlement is not valid for " +
+			"pay quotes")
+
 	case SettlementTypeCredit:
 		expectedAmountSat = 0
 
@@ -232,6 +236,10 @@ func validateInSwapQuote(invoice string, maxFeeSat uint64, cfg *InSwapConfig,
 	expectedAmountSat := amountSat + cfg.FeeSat
 	switch cfg.SettlementType {
 	case "", SettlementTypeLightning, SettlementTypeInArk:
+	case SettlementTypeArkChannel:
+		return fmt.Errorf("ark channel settlement is not valid for " +
+			"pay quotes")
+
 	case SettlementTypeCredit:
 		if cfg.Preimage == nil {
 			return fmt.Errorf("credit in-swap config missing " +

sdk/swaps/in_swap_test.go

@@ -363,6 +363,41 @@ func TestValidateInSwapPreviewAllowsCreditOnlyZeroAmount(t *testing.T) {
 	require.NoError(t, err)
 }
 
+// TestInSwapValidationRejectsArkChannelSettlement verifies the receive-only
+// settlement result cannot be supplied as a pay-side quote.
+func TestInSwapValidationRejectsArkChannelSettlement(t *testing.T) {
+	t.Parallel()
+
+	serverPriv, err := btcec.NewPrivateKey()
+	require.NoError(t, err)
+
+	preimage, err := NewPreimage()
+	require.NoError(t, err)
+	invoice := testValidPayInvoice(t, preimage)
+
+	quote := &InSwapQuote{
+		PaymentHash:      preimage.Hash(),
+		InvoiceAmountSat: testInSwapInvoiceSat,
+		AmountSat:        testInSwapAmountSat,
+		FeeSat:           testInSwapFeeSat,
+		Expiry:           time.Now().Add(time.Minute),
+		SettlementType:   SettlementTypeArkChannel,
+	}
+	err = validateInSwapPreview(
+		invoice, quote, &chaincfg.RegressionNetParams,
+	)
+	require.ErrorContains(t, err, "not valid for pay quotes")
+
+	cfg := testInSwapConfig(
+		serverPriv.PubKey(), preimage, time.Now().Add(time.Minute),
+	)
+	cfg.SettlementType = SettlementTypeArkChannel
+	err = validateInSwapQuote(
+		invoice, testInSwapFeeSat, cfg, &chaincfg.RegressionNetParams,
+	)
+	require.ErrorContains(t, err, "not valid for pay quotes")
+}
+
 // TestValidateInSwapQuoteRejectsServerMismatches verifies the client treats
 // the swap server response as a quote that must match the caller's invoice.
 func TestValidateInSwapQuoteRejectsServerMismatches(t *testing.T) {