feat(sca): cap per-order total ro prevent oversize charges (#26)

api/handlers/cart.go

@@ -23,13 +23,14 @@ import (
 )
 
 type CartHandler struct {
-	stripeKey string
+	stripeKey     string
-	appURL    string
+	appURL        string
+	maxOrderCents int
 }
 
 // NewCartHandler creates a new cart handler with the Stripe secret key
-func NewCartHandler(stripeSecretKey, appURL string) *CartHandler {
+func NewCartHandler(stripeSecretKey, appURL string, maxOrderCents int) *CartHandler {
-	return &CartHandler{stripeKey: stripeSecretKey, appURL: appURL}
+	return &CartHandler{stripeKey: stripeSecretKey, appURL: appURL, maxOrderCents: maxOrderCents}
 }
 
 // getOrCreateCart finds the users cart or creates one.
@@ -354,6 +355,17 @@ func (h *CartHandler) ConvertCart(w http.ResponseWriter, r *http.Request) {
 
 	total := subtotal + cart.ShippingCost
 
+	if h.maxOrderCents > 0 && total > h.maxOrderCents {
+		middleware.RecordCartConversion("validation_over_limit")
+		utils.RespondError(w, http.StatusBadRequest, "CART_OVER_LIMIT",
+			fmt.Sprintf("order total must be at most $%.2f", float64(h.maxOrderCents)/100),
+			map[string]interface{}{
+				"total_cents": total,
+				"limit_cents": h.maxOrderCents,
+			})
+		return
+	}
+
 	if total < 50 {
 		middleware.RecordCartConversion("validation_min_amount")
 		utils.RespondError(w, http.StatusBadRequest, "VALIDATION_ERROR", "order total must be at least $0.50", nil)

api/handlers/cart_test.go

@@ -65,7 +65,7 @@ func TestGetCartEmpty(t *testing.T) {
 	defer func() { _ = os.Remove(testDB) }()
 	defer database.ResetForTesting()
 
-	handler := NewCartHandler("", "")
+	handler := NewCartHandler("", "", 0)
 
 	req := authRequest("GET", "/api/v1/cart", nil, user.ID)
 	w := httptest.NewRecorder()
@@ -104,7 +104,7 @@ func TestSetItemAndGetCart(t *testing.T) {
 	defer func() { _ = os.Remove(testDB) }()
 	defer database.ResetForTesting()
 
-	handler := NewCartHandler("", "")
+	handler := NewCartHandler("", "", 0)
 
 	// Add item (CoffeeID=1, Quantity=2)
 	body, _ := json.Marshal(map[string]interface{}{
@@ -160,7 +160,7 @@ func TestSetItemUpdateQuantity(t *testing.T) {
 	defer func() { _ = os.Remove(testDB) }()
 	defer database.ResetForTesting()
 
-	handler := NewCartHandler("", "")
+	handler := NewCartHandler("", "", 0)
 
 	// Add item
 	body, _ := json.Marshal(map[string]interface{}{"coffee_id": 1, "quantity": 2})
@@ -205,7 +205,7 @@ func TestSetItemRemove(t *testing.T) {
 	defer func() { _ = os.Remove(testDB) }()
 	defer database.ResetForTesting()
 
-	handler := NewCartHandler("", "")
+	handler := NewCartHandler("", "", 0)
 
 	// Add item
 	body, _ := json.Marshal(map[string]interface{}{"coffee_id": 1, "quantity": 3})
@@ -244,7 +244,7 @@ func TestSetItemInvalidProduct(t *testing.T) {
 	defer func() { _ = os.Remove(testDB) }()
 	defer database.ResetForTesting()
 
-	handler := NewCartHandler("", "")
+	handler := NewCartHandler("", "", 0)
 
 	body, _ := json.Marshal(map[string]interface{}{"coffee_id": 999, "quantity": 1})
 	req := authRequest("PUT", "/api/v1/cart/item", body, user.ID)
@@ -261,7 +261,7 @@ func TestSetItemMissingCoffeeID(t *testing.T) {
 	defer func() { _ = os.Remove(testDB) }()
 	defer database.ResetForTesting()
 
-	handler := NewCartHandler("", "")
+	handler := NewCartHandler("", "", 0)
 
 	body, _ := json.Marshal(map[string]interface{}{"quantity": 1})
 	req := authRequest("PUT", "/api/v1/cart/item", body, user.ID)
@@ -278,7 +278,7 @@ func TestClearCart(t *testing.T) {
 	defer func() { _ = os.Remove(testDB) }()
 	defer database.ResetForTesting()
 
-	handler := NewCartHandler("", "")
+	handler := NewCartHandler("", "", 0)
 
 	// Add two items
 	for _, coffeeID := range []uint{1, 2} {
@@ -334,7 +334,7 @@ func TestSetAddress(t *testing.T) {
 	}
 	db.Create(&addr)
 
-	handler := NewCartHandler("", "")
+	handler := NewCartHandler("", "", 0)
 
 	body, _ := json.Marshal(map[string]interface{}{"address_id": addr.ID})
 	req := authRequest("PUT", "/api/v1/cart/address", body, user.ID)
@@ -388,7 +388,7 @@ func TestSetAddressWrongUser(t *testing.T) {
 	}
 	db.Create(&addr)
 
-	handler := NewCartHandler("", "")
+	handler := NewCartHandler("", "", 0)
 
 	body, _ := json.Marshal(map[string]interface{}{"address_id": addr.ID})
 	req := authRequest("PUT", "/api/v1/cart/address", body, user.ID)
@@ -416,7 +416,7 @@ func TestSetCard(t *testing.T) {
 	}
 	db.Create(&card)
 
-	handler := NewCartHandler("", "")
+	handler := NewCartHandler("", "", 0)
 
 	body, _ := json.Marshal(map[string]interface{}{"card_id": card.ID})
 	req := authRequest("PUT", "/api/v1/cart/card", body, user.ID)
@@ -468,7 +468,7 @@ func TestSetCardWrongUser(t *testing.T) {
 	}
 	db.Create(&card)
 
-	handler := NewCartHandler("", "")
+	handler := NewCartHandler("", "", 0)
 
 	body, _ := json.Marshal(map[string]interface{}{"card_id": card.ID})
 	req := authRequest("PUT", "/api/v1/cart/card", body, user.ID)
@@ -485,7 +485,7 @@ func TestConvertCartMissingAddress(t *testing.T) {
 	defer func() { _ = os.Remove(testDB) }()
 	defer database.ResetForTesting()
 
-	handler := NewCartHandler("", "")
+	handler := NewCartHandler("", "", 0)
 
 	// Add item but no address or card
 	body, _ := json.Marshal(map[string]interface{}{"coffee_id": 1, "quantity": 1})
@@ -508,7 +508,7 @@ func TestConvertCartMissingCard(t *testing.T) {
 	defer func() { _ = os.Remove(testDB) }()
 	defer database.ResetForTesting()
 
-	handler := NewCartHandler("", "")
+	handler := NewCartHandler("", "", 0)
 	db := database.GetDB()
 
 	// Add item and address
@@ -539,7 +539,7 @@ func TestConvertCartEmpty(t *testing.T) {
 	defer func() { _ = os.Remove(testDB) }()
 	defer database.ResetForTesting()
 
-	handler := NewCartHandler("", "")
+	handler := NewCartHandler("", "", 0)
 
 	// Empty cart convert
 	req := authRequest("POST", "/api/v1/cart/convert", nil, user.ID)
@@ -556,7 +556,7 @@ func TestMultipleItems(t *testing.T) {
 	defer func() { _ = os.Remove(testDB) }()
 	defer database.ResetForTesting()
 
-	handler := NewCartHandler("", "")
+	handler := NewCartHandler("", "", 0)
 
 	// Add three different items
 	for i := uint(1); i <= 3; i++ {
@@ -605,7 +605,7 @@ func TestCartIsolation(t *testing.T) {
 	}
 	db.Create(&user2)
 
-	handler := NewCartHandler("", "")
+	handler := NewCartHandler("", "", 0)
 	r := chi.NewRouter()
 	r.Put("/cart/item", handler.SetItem)
 	r.Get("/cart", handler.GetCart)
@@ -664,3 +664,103 @@ func TestCartIsolation(t *testing.T) {
 		t.Errorf("User 2 expected coffee_id 2, got %d", resp.Data.Cart.Items[0].CoffeeID)
 	}
 }
+
+func TestConvertCartLimit(t *testing.T) {
+	cases := []struct {
+		name          string
+		capCents      int
+		quantity      int
+		expectOverCap bool
+	}{
+		{"over cap rejects", 20000, 41, true},   // $205
+		{"at cap accepts", 20000, 40, false},    // $200 boundary
+		{"under cap accepts", 20000, 39, false}, // $195
+		{"zero cap disables", 0, 1000, false},   // explicit off-switch
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			testDB, user := setupCartTestDB(t)
+			defer func() { _ = os.Remove(testDB) }()
+			defer database.ResetForTesting()
+
+			db := database.GetDB()
+			user.StripeCustomerID = "cus_test_overlimit"
+			if err := db.Save(&user).Error; err != nil {
+				t.Fatalf("saved user: %v", err)
+			}
+
+			addr := models.Address{
+				UserID: user.ID, Name: "Test", Street: "1 Main St",
+				City: "PDX", State: "OR", Zip: "97201", Country: "US",
+			}
+			if err := db.Create(&addr).Error; err != nil {
+				t.Fatalf("seed address: %v", err)
+			}
+
+			card := models.Card{
+				UserID: user.ID, StripePaymentID: "pm_test_overlimit",
+				Last4: "4242", Brand: "Visa", ExpMonth: 12, ExpYear: 2030,
+			}
+			if err := db.Create(&card).Error; err != nil {
+				t.Fatalf("seed card: %v", err)
+			}
+
+			handler := NewCartHandler("", "", tc.capCents)
+
+			body, _ := json.Marshal(map[string]interface{}{"coffee_id": 4, "quantity": tc.quantity})
+			req := authRequest("PUT", "/api/v1/cart/item", body, user.ID)
+			w := httptest.NewRecorder()
+			handler.SetItem(w, req)
+			if w.Code != http.StatusOK {
+				t.Fatalf("SetItem: %d %s", w.Code, w.Body.String())
+			}
+
+			// set address
+			body, _ = json.Marshal(map[string]interface{}{"address_id": addr.ID})
+			req = authRequest("PUT", "/api/v1/cart/address", body, user.ID)
+			w = httptest.NewRecorder()
+			handler.SetAddress(w, req)
+			if w.Code != http.StatusOK {
+				t.Fatalf("SetAddress: %d %s", w.Code, w.Body.String())
+			}
+
+			// set card
+			body, _ = json.Marshal(map[string]interface{}{"card_id": card.ID})
+			req = authRequest("PUT", "/api/v1/cart/card", body, user.ID)
+			w = httptest.NewRecorder()
+			handler.SetCard(w, req)
+			if w.Code != http.StatusOK {
+				t.Fatalf("SetCard: %d %s", w.Code, w.Body.String())
+			}
+
+			// Convert
+			req = authRequest("POST", "/api/v1/cart/convert", nil, user.ID)
+			w = httptest.NewRecorder()
+			handler.ConvertCart(w, req)
+
+			var resp struct {
+				Success bool `json:"success"`
+				Error   struct {
+					Code    string                 `json:"code"`
+					Message string                 `json:"message"`
+					Details map[string]interface{} `json:"details"`
+				} `json:"error"`
+			}
+			_ = json.NewDecoder(w.Body).Decode(&resp)
+
+			isOverCap := w.Code == http.StatusBadRequest && resp.Error.Code == "CART_OVER_LIMIT"
+			if isOverCap != tc.expectOverCap {
+				t.Fatalf("expectOverCap=%v got code=%d errCode=%q msg=%q", tc.expectOverCap, w.Code, resp.Error.Code, resp.Error.Message)
+			}
+			if tc.expectOverCap {
+				if got, _ := resp.Error.Details["limit_cents"].(float64); int(got) != tc.capCents {
+					t.Errorf("limit_cents in details: want %d, got %v", tc.capCents, resp.Error.Details["limit_cents"])
+				}
+				if got, _ := resp.Error.Details["total_cents"].(float64); int(got) != tc.quantity*500 {
+					t.Errorf("total_cents in details: want %d, got %v", tc.quantity*500, resp.Error.Details["total_cents"])
+				}
+			}
+		})
+	}
+}

api/main.go

@@ -71,7 +71,7 @@ func main() {
 	jwtManager := auth.NewJWTManager(cfg.JWTSecret, 30*time.Minute)
 
 	// Setup routes
-	router := routes.SetupRoutes(version, cfg.StripeSecretKey, cfg.StripeWebhookSecret, jwtManager, cfg.AuthFingerprintKey, cfg.ShippoAPIKey, cfg.BringAPIUID, cfg.BringAPIKey, cfg.BringCustomerNumber, cfg.ShippoWebhookSecret, cfg.AppURL, cfg.SlackSigningSecret, cfg.AdminAPIKey, cfg.APIPort)
+	router := routes.SetupRoutes(version, cfg.StripeSecretKey, cfg.StripeWebhookSecret, jwtManager, cfg.AuthFingerprintKey, cfg.ShippoAPIKey, cfg.BringAPIUID, cfg.BringAPIKey, cfg.BringCustomerNumber, cfg.ShippoWebhookSecret, cfg.AppURL, cfg.SlackSigningSecret, cfg.AdminAPIKey, cfg.APIPort, cfg.MaxOrderCents)
 
 	// Create HTTP server
 	server := &http.Server{

api/routes/routes.go

@@ -29,6 +29,7 @@ func SetupRoutes(
 	slackSigningSecret string,
 	adminAPIKey string,
 	apiPort string,
+	maxOrderCents int,
 ) *chi.Mux {
 	r := chi.NewRouter()
 
@@ -46,7 +47,7 @@ func SetupRoutes(
 	healthHandler := handlers.NewHealthHandler(version)
 	productHandler := handlers.NewProductHandler()
 	authHandler := handlers.NewAuthHandler(jwtManager, authFingerprintKey)
-	cartHandler := handlers.NewCartHandler(stripeSecretKey, appURL)
+	cartHandler := handlers.NewCartHandler(stripeSecretKey, appURL, maxOrderCents)
 	cardHandler := handlers.NewCardHandler(stripeSecretKey, appURL)
 	orderHandler := handlers.NewOrderHandler(stripeSecretKey, bringAPIUID, bringAPIKey, bringCustomerNumber)
 	addressHandler := handlers.NewAddressHandler(shippoAPIKey, bringAPIUID, bringAPIKey)

pkg/config/config.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"net/url"
 	"os"
+	"strconv"
 	"strings"
 
 	"github.com/joho/godotenv"
@@ -30,6 +31,7 @@ type Config struct {
 	ShippoWebhookSecret string
 	SlackSigningSecret  string
 	AdminAPIKey         string
+	MaxOrderCents       int
 }
 
 // Load reads configuration from environment variables and validates required secrets.
@@ -66,6 +68,7 @@ func Load() (*Config, error) {
 		ShippoWebhookSecret: os.Getenv("SHIPPO_WEBHOOK_SECRET"),
 		SlackSigningSecret:  os.Getenv("SLACK_SIGNING_SECRET"),
 		AdminAPIKey:         os.Getenv("ADMIN_API_KEY"),
+		MaxOrderCents:       loadMaxOrderCents(),
 	}
 
 	if err := cfg.validate(); err != nil {
@@ -130,3 +133,20 @@ func getEnvOrDefault(key, defaultValue string) string {
 	}
 	return defaultValue
 }
+
+// loadMaxOrderCents reads MAX_ORDER_CENTS. Default $200. Explicit 0 disables
+// the cap. Garbage or negative values fall back to the default with a warning
+// so an operator typo cannot silently disable a fraud control.
+func loadMaxOrderCents() int {
+	const defaultCap = 20000
+	raw := os.Getenv("MAX_ORDER_CENTS")
+	if raw == "" {
+		return defaultCap
+	}
+	n, err := strconv.Atoi(raw)
+	if err != nil || n < 0 {
+		fmt.Printf("WARNING: MAX_ORDER_CENTS=%q invalid, falling back to default %d\n", raw, defaultCap)
+		return defaultCap
+	}
+	return n
+}

pkg/config/config_test.go

@@ -0,0 +1,34 @@
+package config
+
+import (
+	"testing"
+)
+
+func TestLoadMaxOrderCents(t *testing.T) {
+	cases := []struct {
+		name string
+		env  string // "" means unset
+		want int
+	}{
+		{"unset uses default", "", 20000},
+		{"explicit zero disables", "0", 0},
+		{"valid override", "50000", 50000},
+		{"negative falls back to default", "-1", 20000},
+		{"garbage falls back to default", "two hundred", 20000},
+		{"empty after trim falls back to default", "", 20000},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			if tc.env == "" {
+				t.Setenv("MAX_ORDER_CENTS", "")
+			} else {
+				t.Setenv("MAX_ORDER_CENTS", tc.env)
+			}
+			got := loadMaxOrderCents()
+			if got != tc.want {
+				t.Errorf("loadMaxOrderCents() = %d, want %d", got, tc.want)
+			}
+		})
+	}
+}

pkg/tui/confirmation.go

@@ -333,6 +333,8 @@ func (m Model) ReviewUpdate(msg tea.Msg) (Model, tea.Cmd) {
 func friendlyCheckoutError(raw error) string {
 	s := raw.Error()
 	switch {
+	case strings.Contains(s, "CART_OVER_LIMIT"):
+		return "order total is over the per-order limit. remove items and try again."
 	case strings.Contains(s, "AUTHENTICATION_REQUIRED"):
 		return "your bank wants to verify this charge, authentication step coming soon."
 	case strings.Contains(s, "AUTHENTICATION_NOT_SUPPORTED"):