diff --git a/internal/api/handler_ri_exchange_execute_roundtrip_test.go b/internal/api/handler_ri_exchange_execute_roundtrip_test.go
new file mode 100644
index 000000000..e2e60d2e8
--- /dev/null
+++ b/internal/api/handler_ri_exchange_execute_roundtrip_test.go
@@ -0,0 +1,118 @@
+package api
+
+import (
+	"context"
+	"testing"
+
+	"github.com/LeanerCloud/cloud-commitments-go/pkg/exchange"
+	"github.com/aws/aws-lambda-go/events"
+	"github.com/aws/aws-sdk-go-v2/aws"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// executeExchangeCaptured runs the handler with body and returns the request it
+// handed to the exchange library, the real callee of POST /api/ri-exchange/execute.
+func executeExchangeCaptured(t *testing.T, body string) exchange.ExchangeExecuteRequest {
+	t.Helper()
+	var got exchange.ExchangeExecuteRequest
+	h := awsAuditHandler(t, newDirectExchangeAuditStore(), func(_ context.Context, req exchange.ExchangeExecuteRequest) (string, *exchange.ExchangeQuoteSummary, error) {
+		got = req
+		return "riex-0f1e2d3c", &exchange.ExchangeQuoteSummary{PaymentDueUSDStr: "40.250000", PaymentDueRaw: "40.25", CurrencyCode: "USD"}, nil
+	})
+	_, err := h.executeExchange(auditRequest(context.Background(), body))
+	require.NoError(t, err)
+	return got
+}
+
+// Every field of ExchangeExecuteRequestBody must reach the library request:
+// a dropped field would change what AWS exchanges or the cap it is bound by.
+func TestExecuteExchange_EveryBodyFieldReachesTheLibraryRequest(t *testing.T) {
+	t.Run("targets array", func(t *testing.T) {
+		got := executeExchangeCaptured(t, awsAuditBody)
+
+		assert.Equal(t, "eu-central-1", got.Region)
+		assert.Equal(t, []string{"ri-0a1b2c3d", "ri-4e5f6a7b"}, got.ReservedIDs)
+		assert.Equal(t, []exchange.TargetConfig{
+			{OfferingID: auditOfferingA, Count: 2},
+			{OfferingID: auditOfferingB, Count: 1},
+		}, got.Targets)
+		require.NotNil(t, got.MaxPaymentDueUSD)
+		assert.Equal(t, "500.00", got.MaxPaymentDueUSD.FloatString(2))
+		assert.Empty(t, got.TargetOfferingID)
+		assert.Zero(t, got.TargetCount)
+	})
+
+	t.Run("legacy singleton target", func(t *testing.T) {
+		got := executeExchangeCaptured(t, `{
+			"ri_ids": ["ri-0a1b2c3d"],
+			"target_offering_id": "`+auditOfferingA+`",
+			"target_count": 3,
+			"max_payment_due_usd": "75.50",
+			"region": "us-west-2"
+		}`)
+
+		assert.Equal(t, "us-west-2", got.Region)
+		assert.Equal(t, []string{"ri-0a1b2c3d"}, got.ReservedIDs)
+		assert.Nil(t, got.Targets, "the legacy fields are forwarded as-is, not folded into targets")
+		assert.Equal(t, auditOfferingA, got.TargetOfferingID)
+		assert.Equal(t, int32(3), got.TargetCount)
+		require.NotNil(t, got.MaxPaymentDueUSD)
+		assert.Equal(t, "75.50", got.MaxPaymentDueUSD.FloatString(2))
+	})
+}
+
+// quoteCaptured runs getExchangeQuote with body and returns the request it handed
+// to the exchange library.
+func quoteCaptured(t *testing.T, body string) exchange.ExchangeQuoteRequest {
+	t.Helper()
+	var got exchange.ExchangeQuoteRequest
+	h := &Handler{
+		auth: &mockAuthForExchange{},
+		exchangeQuoteFn: func(_ context.Context, req exchange.ExchangeQuoteRequest) (*exchange.ExchangeQuoteSummary, error) {
+			got = req
+			return &exchange.ExchangeQuoteSummary{IsValidExchange: true}, nil
+		},
+	}
+	h.awsCfgOnce.Do(func() { h.awsCfg = aws.Config{Region: "us-east-1"} })
+	_, err := h.getExchangeQuote(context.Background(), &events.LambdaFunctionURLRequest{
+		Headers: map[string]string{"authorization": "Bearer test-token"},
+		Body:    body,
+	})
+	require.NoError(t, err)
+	return got
+}
+
+// Every field of ExchangeQuoteRequestBody must reach the library request, so the
+// quote prices the exchange the caller asked for.
+func TestGetExchangeQuote_EveryBodyFieldReachesTheLibraryRequest(t *testing.T) {
+	t.Run("targets array", func(t *testing.T) {
+		got := quoteCaptured(t, `{
+			"ri_ids": ["ri-0a1b2c3d", "ri-4e5f6a7b"],
+			"targets": [{"offering_id": "`+auditOfferingA+`", "count": 2}, {"offering_id": "`+auditOfferingB+`", "count": 1}],
+			"region": "eu-central-1"
+		}`)
+
+		assert.Equal(t, "eu-central-1", got.Region)
+		assert.Equal(t, []string{"ri-0a1b2c3d", "ri-4e5f6a7b"}, got.ReservedIDs)
+		assert.Equal(t, []exchange.TargetConfig{
+			{OfferingID: auditOfferingA, Count: 2},
+			{OfferingID: auditOfferingB, Count: 1},
+		}, got.Targets)
+		assert.Empty(t, got.TargetOfferingID)
+		assert.Zero(t, got.TargetCount)
+	})
+
+	t.Run("legacy singleton target", func(t *testing.T) {
+		got := quoteCaptured(t, `{
+			"ri_ids": ["ri-0a1b2c3d"],
+			"target_offering_id": "`+auditOfferingA+`",
+			"target_count": 3
+		}`)
+
+		assert.Equal(t, []string{"ri-0a1b2c3d"}, got.ReservedIDs)
+		assert.Nil(t, got.Targets, "the legacy fields are forwarded as-is, not folded into targets")
+		assert.Equal(t, auditOfferingA, got.TargetOfferingID)
+		assert.Equal(t, int32(3), got.TargetCount)
+	})
+}