diff --git a/backend/handlers/payments/handlers.go b/backend/handlers/payments/handlers.go
index 8368017..8fda619 100644
--- a/backend/handlers/payments/handlers.go
+++ b/backend/handlers/payments/handlers.go
@@ -1941,6 +1941,13 @@ func CreateTipPayment(w http.ResponseWriter, r *http.Request) {
 
 	// Step 2: DB transaction committed — safe to call Square now.
 	// If Square fails, the record stays 'pending' for manual retry.
+
+	// Resolve the user's email for Square receipt delivery.
+	var buyerEmail string
+	if err := db.Conn.QueryRow(r.Context(), `SELECT email FROM users WHERE id = $1`, userID).Scan(&buyerEmail); err != nil {
+		log.Printf("[SQUARE-PROD] Failed to resolve buyer email for user %s: %v (Square receipts will not be emailed)", userID, err)
+	}
+
 	paymentReq := square.CreatePaymentReq{
 		Amount:         req.Amount,
 		Currency:       "GBP",
@@ -1948,6 +1955,7 @@ func CreateTipPayment(w http.ResponseWriter, r *http.Request) {
 		IdempotencyKey: idempotencyKey,
 		ReferenceID:    bookingID,
 		Note:           "tip",
+		BuyerEmail:     buyerEmail,
 	}
 
 	paymentResult, err := SquareClient.CreatePayment(r.Context(), paymentReq)
diff --git a/backend/handlers/payments/payments_test.go b/backend/handlers/payments/payments_test.go
index 44494ff..e919540 100644
--- a/backend/handlers/payments/payments_test.go
+++ b/backend/handlers/payments/payments_test.go
@@ -15,6 +15,7 @@ import (
 
 	"crussell/clock"
 	"crussell/db"
+	"crussell/internal/square"
 	"crussell/mw"
 	"crussell/testutils"
 	"crussell/testutils/fixtures"
@@ -22,6 +23,8 @@ import (
 
 	"github.com/go-chi/chi/v5"
 	"github.com/jackc/pgx/v5"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 func makePaymentRequest(handler http.HandlerFunc, method, path string, body interface{}, token string, ctx context.Context) *httptest.ResponseRecorder {
@@ -1858,6 +1861,59 @@ func TestTipPayment_MultipleTipsAllowed(t *testing.T) {
 	}
 }
 
+func TestTipPayment_WithSavedCard(t *testing.T) {
+	t.Parallel()
+	ctx, tx := testutils.SetupTestTx(t)
+
+	userID, bookingID, _ := setupTestData(t, ctx, tx)
+	userToken := jwt.GenerateUserToken(userID)
+
+	// Create a completed payment so the tip is allowed.
+	payID, err := fixtures.CreateTestPayment(tx, bookingID, 5000.00, "online_square", "full", "completed")
+	require.NoError(t, err)
+	squarePayID := "sqp_test_saved_card"
+	_, err = tx.Exec(ctx, "UPDATE payments SET square_payment_id = $1 WHERE id = $2", squarePayID, payID)
+	require.NoError(t, err)
+
+	// Register the payment in the mock so the tip flow works.
+	mockClient, ok := SquareClient.(*square.MockClient)
+	require.True(t, ok, "SquareClient must be a MockClient for this test")
+	_, err = mockClient.CreatePayment(ctx, square.CreatePaymentReq{
+		Amount:         5000,
+		Currency:       "GBP",
+		SourceID:       "cnon:visa",
+		IdempotencyKey: "pay-for-saved-card-tip",
+		ReferenceID:    bookingID,
+	})
+	require.NoError(t, err)
+
+	// Create a saved card for this user.
+	var savedCardID string
+	err = tx.QueryRow(ctx, `
+		INSERT INTO user_saved_cards (user_id, square_card_id, brand, last_4, exp_month, exp_year, fingerprint)
+		VALUES ($1, 'ccof_mock_saved', 'VISA', '1111', 12, 2030, 'sqfp_mock_saved')
+		RETURNING id
+	`, userID).Scan(&savedCardID)
+	require.NoError(t, err)
+
+	req := CreateTipPaymentRequest{
+		Amount: 1000,
+		CardID: &savedCardID,
+	}
+
+	handler := CreateTipPayment
+	w := makePaymentRequest(handler, "POST", "/api/bookings/"+bookingID+"/tip", req, userToken, ctx)
+	require.Equal(t, http.StatusOK, w.Code, "body: %s", w.Body.String())
+
+	var resp PaymentResponse
+	require.NoError(t, parsePaymentResponseBody(w, &resp))
+	assert.Equal(t, "tip", resp.PaymentType)
+	assert.Equal(t, int64(1000), resp.Amount)
+	assert.Equal(t, "completed", resp.Status)
+	assert.NotEmpty(t, resp.CardBrand)
+	assert.NotEmpty(t, resp.CardLast4)
+}
+
 func TestTipPayment_TransactionFailure_SkipsSquare(t *testing.T) {
 	t.Parallel()
 	ctx, tx := testutils.SetupTestTx(t)
diff --git a/backend/handlers/payments/refunds.go b/backend/handlers/payments/refunds.go
index 1950bf4..f3781fa 100644
--- a/backend/handlers/payments/refunds.go
+++ b/backend/handlers/payments/refunds.go
@@ -6,6 +6,7 @@ import (
 	"log"
 	"log/slog"
 	"math"
+	"strconv"
 	"time"
 
 	"crussell/clock"
@@ -540,10 +541,12 @@ func ProcessPendingSquareRefunds(ctx context.Context, bookingID string, reason s
 		}
 
 		refundCents := int64(math.Round(pr.Amount * 100))
+		// Deterministic idempotency key derived from refund record ID and amount,
+		// so retries (network timeout, proxy, etc.) don't create duplicate Square refunds.
 		refundReq := square.RefundPaymentReq{
 			PaymentID:      *pr.SquarePaymentID,
 			Amount:         refundCents,
-			IdempotencyKey: pr.ID + "-square-" + clock.Now().Format("20060102150405"),
+			IdempotencyKey: pr.ID + "-square-" + strconv.FormatInt(refundCents, 10),
 			Reason:         reason,
 		}
 		sqResult, sqErr := SquareClient.RefundPayment(ctx, refundReq)
diff --git a/backend/handlers/payments/validators.go b/backend/handlers/payments/validators.go
index e1ddaa0..6f001b2 100644
--- a/backend/handlers/payments/validators.go
+++ b/backend/handlers/payments/validators.go
@@ -53,9 +53,15 @@ func ValidateRefundReason(reason string) error {
 	return nil
 }
 
-// ValidateCardInfo checks that at least one of cardID or newCardToken is provided
+// ValidateCardInfo checks that exactly one of cardID or newCardToken is provided,
+// non-nil, and non-empty.
 func ValidateCardInfo(cardID, newCardToken *string) error {
-	if cardID == nil && (newCardToken == nil || *newCardToken == "") {
+	hasCardID := cardID != nil && *cardID != ""
+	hasToken := newCardToken != nil && *newCardToken != ""
+	if hasCardID && hasToken {
+		return errors.New("provide either card_id or new_card_token, not both")
+	}
+	if !hasCardID && !hasToken {
 		return errors.New("either card_id or new_card_token is required")
 	}
 	return nil
diff --git a/backend/internal/square/square_dev.go b/backend/internal/square/square_dev.go
index 1952b07..695b4d0 100644
--- a/backend/internal/square/square_dev.go
+++ b/backend/internal/square/square_dev.go
@@ -463,3 +463,10 @@ func isAllDigits(s string) bool {
 	}
 	return len(s) > 0
 }
+
+func realBaseURL(env string) string {
+	if env == "production" {
+		return squareProductionURL
+	}
+	return squareSandboxURL
+}
diff --git a/backend/internal/square/square_http_client.go b/backend/internal/square/square_http_client.go
index e492acd..bbed742 100644
--- a/backend/internal/square/square_http_client.go
+++ b/backend/internal/square/square_http_client.go
@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"io"
 	"net/http"
+	"net/url"
 	"os"
 	"time"
 )
@@ -339,8 +340,15 @@ func refundPaymentHTTP(ctx context.Context, req RefundPaymentReq) (*RefundResult
 
 func createCardOnFileHTTP(ctx context.Context, userID, cardToken string) (*CardOnFile, error) {
 	hc := newHTTPClient()
+
+	// Deterministic idempotency key derived from user + card (not time-based)
+	// so that retries with the same details don't create duplicate cards.
+	ikHash := fmt.Sprintf("%x", []byte(userID+"|"+cardToken))
+	if len(ikHash) > 64 {
+		ikHash = ikHash[:64]
+	}
 	body := sqCreateCardRequest{
-		IdempotencyKey: fmt.Sprintf("create-card-%d", time.Now().UnixNano()),
+		IdempotencyKey: fmt.Sprintf("create-card-%s", ikHash),
 		SourceID:       cardToken,
 		Card: sqCardPayload{
 			CustomerID: userID,
@@ -358,7 +366,7 @@ func createCardOnFileHTTP(ctx context.Context, userID, cardToken string) (*CardO
 func getCardsOnFileHTTP(ctx context.Context, userID string) ([]CardOnFile, error) {
 	hc := newHTTPClient()
 	var resp sqListCardsResponse
-	if err := hc.doJSON(ctx, http.MethodGet, "/v2/cards?customer_id="+userID, nil, &resp); err != nil {
+	if err := hc.doJSON(ctx, http.MethodGet, "/v2/cards?customer_id="+url.QueryEscape(userID), nil, &resp); err != nil {
 		return nil, err
 	}
 	cards := make([]CardOnFile, 0, len(resp.Cards))
@@ -416,8 +424,11 @@ func paymentFromSquare(sq *sqPayment) *PaymentResult {
 			r.ExpYear = cd.Card.ExpYear
 		}
 	}
-	if r.CardBrand == "" {
-		r.CardBrand = sq.SourceType
+	if r.CardBrand == "" && sq.CardDetails != nil && sq.CardDetails.Card.ID != "" {
+		r.CardBrand = sq.CardDetails.Card.CardBrand
+	}
+	if r.CardLast4 == "" && sq.CardDetails != nil && sq.CardDetails.Card.ID != "" {
+		r.CardLast4 = sq.CardDetails.Card.Last4
 	}
 	return r
 }
@@ -479,10 +490,3 @@ func firstNonEmpty(vals ...string) string {
 	}
 	return ""
 }
-
-func realBaseURL(env string) string {
-	if env == "production" {
-		return squareProductionURL
-	}
-	return squareSandboxURL
-}
diff --git a/frontend/src/lib/components/account/UserBookingModal.svelte b/frontend/src/lib/components/account/UserBookingModal.svelte
index 879719e..a996fa0 100644
--- a/frontend/src/lib/components/account/UserBookingModal.svelte
+++ b/frontend/src/lib/components/account/UserBookingModal.svelte
@@ -199,8 +199,10 @@ import CardBrandIcon from '$lib/components/payments/CardBrandIcon.svelte';
 	const isTipNewCardExpiryPast = $derived(
 		tipNewCardExpiryParts !== null &&
 			(() => {
-				const expiryDate = new SvelteDate(tipNewCardExpiryParts.year, tipNewCardExpiryParts.month);
-				return expiryDate < new SvelteDate();
+				const expiryYearMonth = tipNewCardExpiryParts.year * 12 + tipNewCardExpiryParts.month;
+				const now = new SvelteDate();
+				const currentYearMonth = now.getFullYear() * 12 + now.getMonth() + 1;
+				return expiryYearMonth < currentYearMonth;
 			})()
 	);
 	const hasTipNewCardInvalidMonth = $derived(/^\d{2}\/\d{2}$/.test(tipNewCardExpiry) && tipNewCardExpiryParts === null);
@@ -322,8 +324,6 @@ import CardBrandIcon from '$lib/components/payments/CardBrandIcon.svelte';
 
 			if (tipShowNewCard || tipSavedCards.length === 0) {
 				body.new_card_token = tipNewCardNumber.replace(/\s/g, '');
-				body.card_expiry = tipNewCardExpiry;
-				body.card_cvc = tipNewCardCVC;
 				body.save_card = tipSaveCardFuture;
 			} else {
 				body.card_id = tipSelectedCardId;
diff --git a/frontend/src/lib/components/booking/BookingFlow.svelte b/frontend/src/lib/components/booking/BookingFlow.svelte
index 07f5467..c1a020c 100644
--- a/frontend/src/lib/components/booking/BookingFlow.svelte
+++ b/frontend/src/lib/components/booking/BookingFlow.svelte
@@ -136,7 +136,7 @@
 	const cardError = $derived(
 		cardNumberTouched && !isValidLuhn(newCardNumber) && newCardNumber.length > 0
 			? 'Invalid card number'
-			: cardExpiryTouched && expiryParts !== null && (() => { const d = new SvelteDate(expiryParts.year, expiryParts.month); return d < new SvelteDate(); })()
+			: cardExpiryTouched && expiryParts !== null && (() => { const em = expiryParts.year * 12 + expiryParts.month; const now2 = new SvelteDate(); const cm = now2.getFullYear() * 12 + now2.getMonth() + 1; return em < cm; })()
 				? 'This card has expired'
 				: cardExpiryTouched && !/^\d{2}\/\d{2}$/.test(newCardExpiry) && newCardExpiry.length > 0
 					? 'Enter expiry as MM/YY'
diff --git a/frontend/src/lib/components/payments/UserPaymentModal.svelte b/frontend/src/lib/components/payments/UserPaymentModal.svelte
index 9c59a29..525620c 100644
--- a/frontend/src/lib/components/payments/UserPaymentModal.svelte
+++ b/frontend/src/lib/components/payments/UserPaymentModal.svelte
@@ -79,8 +79,10 @@
 	const isExpiryInPast = $derived(
 		expiryParts !== null &&
 			(() => {
-				const expiryDate = new SvelteDate(expiryParts.year, expiryParts.month);
-				return expiryDate < new SvelteDate();
+				const expiryYearMonth = expiryParts.year * 12 + expiryParts.month;
+				const now = new SvelteDate();
+				const currentYearMonth = now.getFullYear() * 12 + now.getMonth() + 1;
+				return expiryYearMonth < currentYearMonth;
 			})()
 	);
 
diff --git a/frontend/src/routes/account/+page.svelte b/frontend/src/routes/account/+page.svelte
index 4b4f55c..65b053b 100644
--- a/frontend/src/routes/account/+page.svelte
+++ b/frontend/src/routes/account/+page.svelte
@@ -201,8 +201,10 @@ import CardBrandIcon from '$lib/components/payments/CardBrandIcon.svelte';
 	const isNewCardExpiryInPast = $derived(
 		newCardExpiryParts !== null &&
 			(() => {
-				const expiryDate = new SvelteDate(newCardExpiryParts.year, newCardExpiryParts.month);
-				return expiryDate < new SvelteDate();
+				const expiryYearMonth = newCardExpiryParts.year * 12 + newCardExpiryParts.month;
+				const now = new SvelteDate();
+				const currentYearMonth = now.getFullYear() * 12 + now.getMonth() + 1;
+				return expiryYearMonth < currentYearMonth;
 			})()
 	);
 	const isNewCardExpiryInvalidMonth = $derived(
@@ -230,8 +232,10 @@ import CardBrandIcon from '$lib/components/payments/CardBrandIcon.svelte';
 	const isBuyNewCardExpiryInPast = $derived(
 		buyNewCardExpiryParts !== null &&
 			(() => {
-				const expiryDate = new SvelteDate(buyNewCardExpiryParts.year, buyNewCardExpiryParts.month);
-				return expiryDate < new SvelteDate();
+				const expiryYearMonth = buyNewCardExpiryParts.year * 12 + buyNewCardExpiryParts.month;
+				const now = new SvelteDate();
+				const currentYearMonth = now.getFullYear() * 12 + now.getMonth() + 1;
+				return expiryYearMonth < currentYearMonth;
 			})()
 	);
 	const isBuyNewCardExpiryInvalidMonth = $derived(
diff --git a/frontend/src/routes/pay-tip/[id]/+page.svelte b/frontend/src/routes/pay-tip/[id]/+page.svelte
index b2d6b47..bff064d 100644
--- a/frontend/src/routes/pay-tip/[id]/+page.svelte
+++ b/frontend/src/routes/pay-tip/[id]/+page.svelte
@@ -112,8 +112,10 @@ import CardBrandIcon from '$lib/components/payments/CardBrandIcon.svelte';
 	const isNewCardExpiryPast = $derived(
 		newCardExpiryParts !== null &&
 			(() => {
-				const expiryDate = new SvelteDate(newCardExpiryParts.year, newCardExpiryParts.month);
-				return expiryDate < new SvelteDate();
+				const expiryYearMonth = newCardExpiryParts.year * 12 + newCardExpiryParts.month;
+				const now = new SvelteDate();
+				const currentYearMonth = now.getFullYear() * 12 + now.getMonth() + 1;
+				return expiryYearMonth < currentYearMonth;
 			})()
 	);
 	const hasNewCardInvalidMonth = $derived(/^\d{2}\/\d{2}$/.test(newCardExpiry) && newCardExpiryParts === null);
@@ -306,8 +308,6 @@ import CardBrandIcon from '$lib/components/payments/CardBrandIcon.svelte';
 
 			if (showNewCardForm || savedCards.length === 0) {
 				body.new_card_token = newCardNumber.replace(/\s/g, '');
-				body.card_expiry = newCardExpiry;
-				body.card_cvc = newCardCVC;
 				body.save_card = saveCardForFuture;
 			} else {
 				body.card_id = selectedCardId;
diff --git a/frontend/src/routes/tip/+page.svelte b/frontend/src/routes/tip/+page.svelte
index 6dd6379..bcefdc2 100644
--- a/frontend/src/routes/tip/+page.svelte
+++ b/frontend/src/routes/tip/+page.svelte
@@ -136,8 +136,12 @@ import CardBrandIcon from '$lib/components/payments/CardBrandIcon.svelte';
 	const isNewCardExpiryPast = $derived(
 		newCardExpiryParts !== null &&
 			(() => {
-				const expiryDate = new SvelteDate(newCardExpiryParts.year, newCardExpiryParts.month);
-				return expiryDate < new SvelteDate();
+				// parseExpiryParts returns months 1-indexed (1=Jan, 12=Dec).
+				// Use year-month arithmetic to avoid Date constructor 0-index confusion.
+				const expiryYearMonth = newCardExpiryParts.year * 12 + newCardExpiryParts.month;
+				const now = new SvelteDate();
+				const currentYearMonth = now.getFullYear() * 12 + now.getMonth() + 1;
+				return expiryYearMonth < currentYearMonth;
 			})()
 	);
 	const hasNewCardInvalidMonth = $derived(/^\d{2}\/\d{2}$/.test(newCardExpiry) && newCardExpiryParts === null);
@@ -253,8 +257,6 @@ import CardBrandIcon from '$lib/components/payments/CardBrandIcon.svelte';
 
 			if (showNewCardForm || savedCards.length === 0) {
 				body.new_card_token = newCardNumber.replace(/\s/g, '');
-				body.card_expiry = newCardExpiry;
-				body.card_cvc = newCardCVC;
 				body.save_card = saveCardForFuture;
 			} else {
 				body.card_id = selectedCardId;
diff --git a/obsidian/Crussell/Future Work - Gap Backlog.md b/obsidian/Crussell/Future Work - Gap Backlog.md
index 63b03d9..a2c69d7 100644
--- a/obsidian/Crussell/Future Work - Gap Backlog.md	
+++ b/obsidian/Crussell/Future Work - Gap Backlog.md	
@@ -33,8 +33,9 @@ These are things that work fine in dev (with mocks) but need real implementation
 | P6 | **Email/SMS notification delivery** | XL (5-7d) | Backend | `user_notification_preferences` table stores delivery preferences. 8 TODO markers reference this blocker. Notification creation works (admin_notifications table), but no delivery channel exists. No SMTP configuration, no SMS provider. 2 tests skipped as "WIP handler." | The notification queue works (reasons, priorities, acknowledging). What's missing is the delivery backend. Affects: slot eviction alerts, edit request approvals/denials, gift card codes, unpaid booking reminders, idle account warnings. |
 | P7 | **Production security headers** | S (1h) | Backend | HSTS and Referrer-Policy headers are commented out in `main.go:231-233` with TODO markers. They were left disabled for dev HTTP convenience. | Uncomment and configure for production. |
 | P8 | **Social auth stubs (Google/Microsoft/Facebook)** | L (2-3d) | Backend + Frontend | `handlers/auth/social.go` is 1 line (`package auth`). Frontend login page has 3 social buttons that show `toast.info("${provider} login coming soon")`. The `user_social_logins` table and `account_type` enum values exist from early schema design. | The schema was designed for social auth from the start (table + enum values). The OAuth flow itself was never implemented. Buttons exist as UI placeholders. |
-| P9 | **Tip payments: replace placeholder card tokens** | S (1d) | Frontend | 3 tip endpoints send `card_token: 'placeholder'` — a literal string. (`UserBookingModal:190`, `tip/+page.svelte:141`, `pay-tip/[id]/+page.svelte:170`). The Square Web Payments token from the frontend card form was never wired. | The tip UI flow works (select amount, confirm). The actual card token from Square's payment form was never plumbed through. Needs to capture the real nonce/token and pass it to the backend. |
+| P9 | **Tip payments: replace placeholder card tokens** | S (1d) | Frontend | ✅ COMPLETED July 2026 — `card_token: 'placeholder'` replaced with real saved card selection + CardInput with Luhn/expiry/CVC validation across all 3 tip pages. | |
 | P10 | **No automated database backups** | M (1d) | Infrastructure | PostgreSQL volume is persistent in Docker but no `pg_dump` cron, no point-in-time recovery. | Standard production DB setup task. |
+| P11 | **Square Web Payments SDK: replace CardInput with nonce-based flow** | M (3-5d) | Frontend + Backend | Frontend still sends raw PAN, expiry, and CVC as `new_card_token` for all card entry flows (tips, booking payment, gift cards, account add card, till purchases). In production, Square's API requires a `cnon:xxx` nonce generated by the Web Payments SDK. The mock (`square_dev.go`) parses raw PANs (detecting brand from first digit), masking this failure in development. | **Action plan:** 1) Load Square Web Payments SDK (script tag in `app.html` or via `@square/web-payments-sdk` npm). 2) Replace `CardInput.svelte` (hand-rolled inputs) with Square's native card form (`payments.card()`). 3) Call `card.tokenize()` to get `cnon:xxx` nonce client-side. 4) Send only the nonce as `new_card_token`. 5) Remove `card_expiry`/`card_cvc` from request bodies (already removed from tip flows). 6) Remove `CreateCardOnFileRaw` from production paths. |
 
 ---
 
@@ -103,11 +104,16 @@ These don't add features but reduce maintenance cost and risk.
 | T10 | **Replace `as any` in HolidayHours** | S (30min) | Frontend | `HolidayHours.svelte:234` — `(group.hours as any[])?.map(…)`. Hours array has known shape. |
 | T11 | **Replace `e: any` in button onclick** | S (30min) | Frontend | `button.svelte:101` — click handler typed as `e: any`. |
 | T12 | **Former name display (4 TODO sites)** | S (1d) | Frontend + Backend | 4 TODOs across GiftCards + notifications needing `previousFirstName`/`previousLastName` from backend. |
-| T13 | **Fix `devProdClient` rune-arithmetic in test** | S (30min) | Backend | `square_dev_test.go:410` — `rune('0'+idx)` breaks for indices >= 10 (`:` not a digit). |
+| T13 | **Fix `devProdClient` rune-arithmetic in test** | S (30min) | Backend | ✅ COMPLETED July 2026 — `rune('0'+idx)` replaced with `fmt.Sprintf("concurrent-key-%d", idx)` for proper numeric formatting beyond index 9. |
 | T14 | **Error tracking / monitoring (Sentry)** | M (1-2d) | Backend | `log.Printf()` only. No alerting on 5xx. 39 ALERT + 11 CRITICAL logs will never be seen. |
 
 ---
 
+## Previously Completed Items (July 2026 backlog)
+
+- ~~**Tip payments: replace placeholder card tokens (P9)** — `card_token: 'placeholder'` replaced with real saved card selection + CardInput + Luhn/expiry/CVC validation across all 3 tip pages. CardBrandIcon SVGs added for all Square-supported brands.~~
+- ~~**Fix `devProdClient` rune-arithmetic in test (T13)** — `rune('0'+idx)` replaced with `fmt.Sprintf("concurrent-key-%d", idx)`.~~
+
 ## Previously Completed Items (June 2026 backlog)
 
 - ~~Reservation/cleanup background cron~~ — All 20 jobs migrated to centralized scheduler