diff --git a/.env.example b/.env.example
index 6cf33f9..52900f5 100644
--- a/.env.example
+++ b/.env.example
@@ -37,6 +37,7 @@ R2_ENDPOINT=
 # Square Payment Gateway
 SQUARE_ACCESS_TOKEN=
 SQUARE_LOCATION_ID=
+SQUARE_TERMINAL_DEVICE_ID=
 SQUARE_ENVIRONMENT=mock
 SQUARE_WEBHOOK_SIGNATURE_KEY=
 SQUARE_WEBHOOK_NOTIFICATION_URL=
diff --git a/README.md b/README.md
index c075269..db59baf 100644
--- a/README.md
+++ b/README.md
@@ -4,9 +4,9 @@ Nail salon booking platform — Go 1.26.5 backend + SvelteKit 5 SPA + PostgreSQL
 
 ## Features
 
-**Booking**: Self-service (customer), walk-in (admin), call-in (admin). Slot reservations prevent double-booking (4 TTL types). **Self-blocking prevention**: `excludeUserID` parameter filters a user's own `RESERVATION` entries from time blocker overlap checks, allowing re-reservation and booking at overlapping slots. **Explicit cancellation**: `DELETE /api/bookings/reserve` releases a user reservation; `DELETE /api/admin/bookings/reserve` releases an admin walk-in/call-in reservation. **Background cleanup**: Centralised cron scheduler (`backend/internal/jobs/`) runs 21 maintenance jobs: reservation/deposit cleanup every 5min, hourly campaign transitions, daily unpaid-booking notifications, staged default hours auto-apply, GDPR anonymization, financial aggregation, and token/code cleanup. Guest accounts with GDPR-compliant anonymization (including `RESERVATION:edit_request:%` scrubbing). Service eligibility based on age + patch test validity. Overlap checks use `FOR UPDATE` row locks inside transactions. Closing-hours validation (`closing_time.go`) resolves both current and staged default hours.
+**Booking**: Self-service (customer), walk-in (admin), call-in (admin). Slot reservations prevent double-booking (4 TTL types). **Self-blocking prevention**: `excludeUserID` parameter filters a user's own `RESERVATION` entries from time blocker overlap checks, allowing re-reservation and booking at overlapping slots. **Explicit cancellation**: `DELETE /api/bookings/reserve` releases a user reservation; `DELETE /api/admin/bookings/reserve` releases an admin walk-in/call-in reservation. **Background cleanup**: Centralised cron scheduler (`backend/internal/jobs/`) runs 22 maintenance jobs: reservation/deposit cleanup every 5min, hourly campaign transitions, daily unpaid-booking notifications, staged default hours auto-apply, GDPR anonymization, financial aggregation, and token/code cleanup. Guest accounts with GDPR-compliant anonymization (including `RESERVATION:edit_request:%` scrubbing). Service eligibility based on age + patch test validity. Overlap checks use `FOR UPDATE` row locks inside transactions. Closing-hours validation (`closing_time.go`) resolves both current and staged default hours.
 
-**Payments**: Square Terminal (in-person, via `CreateTerminalCheckout`) + online card payments via saved cards or new cards tokenized through the Square Web Payments SDK (`cnon:` nonces — gated off in local dev until `VITE_SQUARE_APPLICATION_ID`/`VITE_SQUARE_LOCATION_ID` are set). The backend accepts only tokens, never raw PANs (PCI-DSS parity, mirrored in the dev mock). Cash with change calculation. Gift cards (12-digit code or account balance). Saved cards for faster checkout. Tips on completed bookings. Refunds with notice-period tiers and deposit protection (72h/24h thresholds). All payment types: deposit, full, partial, balance, tip. Payment >20% of total promotes `pending_release` bookings back to `confirmed`. Deposit paid is computed from payments on-the-fly. The first 50% of each payment is always carved out as deposit (via `buildSplitRecords`); any overflow beyond the booking total becomes a tip. A PostgreSQL `pg_advisory_lock` serializes payment attempts per-booking to prevent two-tab double-payment races. Gift card purchases insert a pending payment record with VAT before calling Square — the DB transaction commits first, so Square failures leave a retryable pending record (same-key retries reuse it).
+**Payments**: Square Terminal (in-person, via `CreateTerminalCheckout`) + online card payments via saved cards or new cards tokenized through the Square Web Payments SDK (`cnon:` nonces — gated off in local dev until `VITE_SQUARE_APPLICATION_ID`/`VITE_SQUARE_LOCATION_ID` are set). The backend accepts only tokens, never raw PANs (PCI-DSS parity, mirrored in the dev mock). Cash with change calculation. Gift cards (12-digit code or account balance). Saved cards for faster checkout. Tips on completed bookings. Refunds with notice-period tiers and deposit protection (72h/24h thresholds). All payment types: deposit, full, partial, balance, tip. Payment >20% of total promotes `pending_release` bookings back to `confirmed`. Deposit paid is computed from payments on-the-fly. The first 50% of each payment is always carved out as deposit (via `buildSplitRecords`); any overflow beyond the booking total becomes a tip. A PostgreSQL `pg_advisory_lock` serializes payment attempts per-booking to prevent two-tab double-payment races. Gift card purchases insert a pending payment record with VAT before calling Square — the DB transaction commits first, so Square failures leave a retryable pending record (same-key retries reuse it). Two background sweeps close Square's ~24h idempotency-key retention window: `sweep-pending-square-refunds` reconciles/retries stuck refunds (with a 23h age guard), and `sweep-stale-pending-payments` fails stale pending payments/till-sales so a late retry cannot issue a second charge.
 
 **Gift Cards**: Multi-method purchase (cash, card machine, online card, giveaway). Inventory cards for stock management. 24-month rolling expiry. Idle account cleanup (2yr/5yr thresholds). Expired balance recovery with admin audit trail. Transaction audit log. Idempotency keys for purchases.
 
@@ -18,7 +18,7 @@ Nail salon booking platform — Go 1.26.5 backend + SvelteKit 5 SPA + PostgreSQL
 
 **Loyalty & Discounts**: 1 stamp per paid appointment (max 1/day). 10 stamps → 10% off via opt-in checkbox at payment or till. Stamps refunded on cancellation. Campaigns auto-apply at both payment and completion: time-based, per-user milestone, global milestone (in-person only), anniversary. All discounts stack additively against original total. Discount payment records excluded from refund calculations.
 
-**Compliance**: GDPR Article 15 data export (async, 12h cache, 21-section JSON + PDF — excludes verification codes as authentication tokens). Account deletion with external system scrubbing (S3, Square). Guest PII anonymized 6 months post-appointment. UK financial data retention (7 years). Gift card SPV/MPV VAT treatment configurable.
+**Compliance**: GDPR Article 15 data export (async, 12h cache, 23-section JSON + PDF — excludes verification codes as authentication tokens). Account deletion with external system scrubbing (S3, Square). Guest PII anonymized 6 months post-appointment. UK financial data retention (7 years). Gift card SPV/MPV VAT treatment configurable.
 
 **Frontend**: Portfolio gallery with fuzzy tag search (relevance-sorted) and exact category filters (date-sorted), multi-format images (AVIF/WebP/JPEG/JXL with WASM client-side encoding), cursor-based pagination. MapLibre GL map on contact page. PhoneInput component with UK validation. CharCounter for long notes.
 
@@ -94,6 +94,26 @@ To bypass: `git commit --no-verify`.
 
 CI caches Go modules (`~/go/pkg/mod`) and npm dependencies (`~/.npm`, `node_modules`) via `actions/cache` — keyed on `go.sum` and `package-lock.json` respectively. Cache is served by Gitea's built-in cache server at `git.popertots.com`. First run downloads everything (~3m35s), subsequent runs restore from cache in seconds.
 
+### Database migrations
+
+The schema lives in `init-scripts/init-script.sql` and is applied automatically on a **fresh** volume via `docker-entrypoint-initdb.d`. Existing deployments must apply the payment-system delta manually (the schema is not migration-managed):
+
+```sql
+-- Refund system columns (refunds table)
+ALTER TABLE refunds ADD COLUMN IF NOT EXISTS refund_attempts INT NOT NULL DEFAULT 0;
+ALTER TABLE refunds ADD COLUMN IF NOT EXISTS origin VARCHAR(16) NOT NULL DEFAULT 'manual';
+ALTER TABLE refunds ADD COLUMN IF NOT EXISTS idempotency_key VARCHAR(64) UNIQUE;
+
+-- refund_failed notification reason (admin_notification_reason enum)
+-- NOTE: ALTER TYPE ... ADD VALUE cannot run inside a transaction block; run on a connection with autocommit.
+ALTER TYPE admin_notification_reason ADD VALUE IF NOT EXISTS 'refund_failed';
+
+-- Refunds may now reference non-booking payments (gift-card purchase refunds)
+ALTER TABLE refunds ALTER COLUMN booking_id DROP NOT NULL;
+```
+
+The sweep job (`internal/jobs/cleanup.go`) and `refunds.go` cast `'refund_failed'::admin_notification_reason`, so an un-migrated DB fails at runtime — apply these before deploying the payment changes.
+
 ## Full Documentation
 
 Detailed architecture, schema, admin workflows, user journeys, and backlog in [obsidian/Crussell/](obsidian/Crussell/).
diff --git a/backend/handlers/payments/concurrency_test.go b/backend/handlers/payments/concurrency_test.go
index e7fd8c7..ca21403 100644
--- a/backend/handlers/payments/concurrency_test.go
+++ b/backend/handlers/payments/concurrency_test.go
@@ -12,6 +12,7 @@ import (
 
 	"crussell/db"
 	"crussell/internal/square"
+	"crussell/mw"
 	"crussell/testutils"
 	"crussell/testutils/fixtures"
 	"crussell/testutils/jwt"
@@ -392,7 +393,10 @@ func TestGetCheckoutStatus_ConcurrentPolls_SingleRecord(t *testing.T) {
 			req := httptest.NewRequest("GET", "/api/checkout/"+checkoutID+"/status?booking_id="+bookingID, nil)
 			rctx := chi.NewRouteContext()
 			rctx.URLParams.Add("checkout_id", checkoutID)
-			req = req.WithContext(context.WithValue(req.Context(), chi.RouteCtxKey, rctx))
+			reqCtx := context.WithValue(req.Context(), chi.RouteCtxKey, rctx)
+			// GetCheckoutStatus is admin-only (defense-in-depth S-1 check).
+			reqCtx = context.WithValue(reqCtx, mw.UserRoleKey, "admin")
+			req = req.WithContext(reqCtx)
 			w := httptest.NewRecorder()
 			GetCheckoutStatus(w, req)
 			recs[idx] = w
diff --git a/backend/handlers/payments/giftcards.go b/backend/handlers/payments/giftcards.go
index 195e3cb..91d9c35 100644
--- a/backend/handlers/payments/giftcards.go
+++ b/backend/handlers/payments/giftcards.go
@@ -481,7 +481,7 @@ func TopUpGiftCard(w http.ResponseWriter, r *http.Request) {
 	var redeemedBy sql.NullString
 	var isInventory bool
 	var currentTotalFunds float64
-	err = tx.QueryRow(ctx, "SELECT redeemed_by, is_inventory, total_funds_added FROM gift_cards WHERE id = $1", cardID).Scan(&redeemedBy, &isInventory, &currentTotalFunds)
+	err = tx.QueryRow(ctx, "SELECT redeemed_by, is_inventory, total_funds_added FROM gift_cards WHERE id = $1 FOR UPDATE", cardID).Scan(&redeemedBy, &isInventory, &currentTotalFunds)
 	if err != nil {
 		if errors.Is(err, pgx.ErrNoRows) {
 			http.Error(w, "Gift card not found", http.StatusNotFound)
@@ -597,7 +597,11 @@ func TransferGiftCard(w http.ResponseWriter, r *http.Request) {
 	var fromRedeemedBy, toRedeemedBy sql.NullString
 	var fromRemaining, toRemaining float64
 
-	err = tx.QueryRow(ctx, "SELECT redeemed_by, amount_remaining FROM gift_cards WHERE id = $1", fromCardID).Scan(&fromRedeemedBy, &fromRemaining)
+	// Lock both rows FOR UPDATE (source first, deterministic order) so a
+	// concurrent transfer/topup can't interleave a read-then-write on the same
+	// card — the same check-then-act race RedeemGiftCard and the till path
+	// already guard against (N-5).
+	err = tx.QueryRow(ctx, "SELECT redeemed_by, amount_remaining FROM gift_cards WHERE id = $1 FOR UPDATE", fromCardID).Scan(&fromRedeemedBy, &fromRemaining)
 	if err != nil {
 		if errors.Is(err, pgx.ErrNoRows) {
 			http.Error(w, "Source gift card not found", http.StatusNotFound)
@@ -608,7 +612,7 @@ func TransferGiftCard(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	err = tx.QueryRow(ctx, "SELECT redeemed_by, amount_remaining FROM gift_cards WHERE id = $1", req.ToCardID).Scan(&toRedeemedBy, &toRemaining)
+	err = tx.QueryRow(ctx, "SELECT redeemed_by, amount_remaining FROM gift_cards WHERE id = $1 FOR UPDATE", req.ToCardID).Scan(&toRedeemedBy, &toRemaining)
 	if err != nil {
 		if errors.Is(err, pgx.ErrNoRows) {
 			http.Error(w, "Destination gift card not found", http.StatusNotFound)
@@ -953,6 +957,13 @@ func BuyGiftCard(w http.ResponseWriter, r *http.Request) {
 				reusePendingID = existing.ID
 				log.Printf("[PAYMENTS] Reusing pending payment %s for idempotent gift-card retry (key %s)", existing.ID, req.IdempotencyKey)
 			}
+			if existing.Status == "failed" {
+				// Swept as stale (>24h) or definitively rejected — a retry would
+				// risk a second Square charge. Reject cleanly (R2).
+				log.Printf("Gift card retry rejected: pending record %s was marked failed", existing.ID)
+				http.Error(w, "This gift card purchase previously failed and can no longer be retried", http.StatusConflict)
+				return
+			}
 		}
 	}
 
@@ -1093,8 +1104,26 @@ func BuyGiftCard(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	// Step 3: Square succeeded — update payment, create gift card.
-	_, upErr := db.Conn.Exec(ctx,
+	// Step 3: Square succeeded — atomically flip the payment to completed and
+	// create the gift card + balance + transaction in ONE transaction. If any
+	// step fails, the whole thing rolls back, the payment stays 'pending', and
+	// a same-key retry re-attempts the Square charge (Square dedups) before
+	// delivering the card. Previously these were separate non-transactional
+	// writes: a failure after the payment-completed update left the customer
+	// CHARGED but with no card, and the completed-dedup swallowed the retry.
+	issueTx, err := db.Conn.Begin(ctx)
+	if err != nil {
+		log.Printf("Failed to begin gift-card issue transaction: %v", err)
+		http.Error(w, "internal server error", http.StatusInternalServerError)
+		return
+	}
+	defer func() {
+		if err := issueTx.Rollback(ctx); err != nil && !errors.Is(err, pgx.ErrTxClosed) {
+			slog.Error("failed to rollback gift-card issue transaction", "err", err)
+		}
+	}()
+
+	_, upErr := issueTx.Exec(ctx,
 		`UPDATE payments SET status = 'completed', square_payment_id = $1 WHERE id = $2`,
 		paymentResult.SquarePayID, buyPaymentID,
 	)
@@ -1108,7 +1137,7 @@ func BuyGiftCard(w http.ResponseWriter, r *http.Request) {
 
 	if req.RecipientType == "self" {
 		var purchaseVoucherType string
-		err = db.Conn.QueryRow(ctx, `SELECT COALESCE(voucher_type, 'SPV') FROM business_settings LIMIT 1`).Scan(&purchaseVoucherType)
+		err = issueTx.QueryRow(ctx, `SELECT COALESCE(voucher_type, 'SPV') FROM business_settings LIMIT 1`).Scan(&purchaseVoucherType)
 		if err != nil {
 			log.Printf("Failed to query voucher type: %v", err)
 			http.Error(w, "internal server error", http.StatusInternalServerError)
@@ -1117,7 +1146,7 @@ func BuyGiftCard(w http.ResponseWriter, r *http.Request) {
 		if purchaseVoucherType == "" {
 			purchaseVoucherType = "SPV"
 		}
-		err = db.Conn.QueryRow(ctx, `
+		err = issueTx.QueryRow(ctx, `
 			INSERT INTO gift_cards (total_funds_added, amount_remaining, created_by, redeemed_at, redeemed_by, is_inventory, voucher_type_at_purchase)
 			VALUES ($1, 0, $2, NOW(), $2, FALSE, $3)
 			RETURNING id
@@ -1128,7 +1157,7 @@ func BuyGiftCard(w http.ResponseWriter, r *http.Request) {
 			return
 		}
 
-		_, err = db.Conn.Exec(ctx, `
+		_, err = issueTx.Exec(ctx, `
 			INSERT INTO user_giftcard_balances (user_id, balance, updated_at)
 			VALUES ($1, $2, NOW())
 			ON CONFLICT (user_id) DO UPDATE SET
@@ -1141,7 +1170,7 @@ func BuyGiftCard(w http.ResponseWriter, r *http.Request) {
 			return
 		}
 
-		_, err = db.Conn.Exec(ctx, `
+		_, err = issueTx.Exec(ctx, `
 			INSERT INTO gift_card_transactions (gift_card_id, transaction_type, amount, reference_type, reference_id, user_id, notes)
 			VALUES ($1, 'purchase', $2, 'api', NULL, $3, 'self-purchase, auto-redeemed')
 		`, cardID, amountPounds, userID)
@@ -1152,7 +1181,7 @@ func BuyGiftCard(w http.ResponseWriter, r *http.Request) {
 		}
 	} else {
 		var purchaseVoucherType string
-		err = db.Conn.QueryRow(ctx, `SELECT COALESCE(voucher_type, 'SPV') FROM business_settings LIMIT 1`).Scan(&purchaseVoucherType)
+		err = issueTx.QueryRow(ctx, `SELECT COALESCE(voucher_type, 'SPV') FROM business_settings LIMIT 1`).Scan(&purchaseVoucherType)
 		if err != nil {
 			log.Printf("Failed to query voucher type: %v", err)
 			http.Error(w, "internal server error", http.StatusInternalServerError)
@@ -1161,7 +1190,7 @@ func BuyGiftCard(w http.ResponseWriter, r *http.Request) {
 		if purchaseVoucherType == "" {
 			purchaseVoucherType = "SPV"
 		}
-		err = db.Conn.QueryRow(ctx, `
+		err = issueTx.QueryRow(ctx, `
 			INSERT INTO gift_cards (total_funds_added, amount_remaining, created_by, is_inventory, voucher_type_at_purchase)
 			VALUES ($1, $1, $2, FALSE, $3)
 			RETURNING id
@@ -1175,7 +1204,7 @@ func BuyGiftCard(w http.ResponseWriter, r *http.Request) {
 		recipient := req.RecipientEmail
 		if recipient == "" {
 			var userEmail string
-			err = db.Conn.QueryRow(ctx, "SELECT email FROM users WHERE id = $1", userID).Scan(&userEmail)
+			err = issueTx.QueryRow(ctx, "SELECT email FROM users WHERE id = $1", userID).Scan(&userEmail)
 			if err != nil {
 				log.Printf("Failed to query user email: %v", err)
 				http.Error(w, "internal server error", http.StatusInternalServerError)
@@ -1188,7 +1217,7 @@ func BuyGiftCard(w http.ResponseWriter, r *http.Request) {
 		// code anyone can redeem). Log only the value and recipient for audit.
 		log.Printf("Gift card purchased for friend — value: £%.2f, intended for: %s (code stored in DB, not logged)", amountPounds, recipient)
 
-		_, err = db.Conn.Exec(ctx, `
+		_, err = issueTx.Exec(ctx, `
 			INSERT INTO gift_card_transactions (gift_card_id, transaction_type, amount, reference_type, reference_id, user_id, notes)
 			VALUES ($1, 'purchase', $2, 'api', NULL, $3, 'purchased for friend')
 		`, cardID, amountPounds, userID)
@@ -1199,6 +1228,12 @@ func BuyGiftCard(w http.ResponseWriter, r *http.Request) {
 		}
 	}
 
+	if err := issueTx.Commit(ctx); err != nil {
+		log.Printf("CRITICAL: Square payment succeeded (ID=%s) but gift-card issue transaction commit failed: %v — manual reconciliation required", paymentResult.SquarePayID, err)
+		http.Error(w, "internal server error", http.StatusInternalServerError)
+		return
+	}
+
 	w.WriteHeader(http.StatusCreated)
 	if err := json.NewEncoder(w).Encode(map[string]any{
 		"status": "success",
diff --git a/backend/handlers/payments/handlers.go b/backend/handlers/payments/handlers.go
index 393f714..20d7b5f 100644
--- a/backend/handlers/payments/handlers.go
+++ b/backend/handlers/payments/handlers.go
@@ -3,6 +3,7 @@ package payments
 import (
 	"context"
 	"crypto/rand"
+	"crypto/sha256"
 	"crussell/clock"
 	"crussell/db"
 	"crussell/internal/square"
@@ -31,6 +32,10 @@ type CreateTerminalPaymentRequest struct {
 	TipEnabled     bool    `json:"tip_enabled"`
 	PaymentMethod  *string `json:"payment_method,omitempty"`
 	GiftCardID     *string `json:"gift_card_id,omitempty"`
+	// saved_card_id: the user's saved card (user_saved_cards.id) to charge
+	// directly, bypassing the terminal. The frontend sends this for the admin
+	// "Charge Saved Card" action.
+	UserSavedCardID *string `json:"saved_card_id,omitempty"`
 }
 
 type CreateBookingPaymentRequest struct {
@@ -123,6 +128,15 @@ type DiscountPreview struct {
 	Amount  float64 `json:"amount"`
 }
 
+// isAdminRequest is a defense-in-depth role check for admin-only payment
+// handlers. The routes are mounted under mw.RequireAdmin, but this in-handler
+// guard keeps admin-only actions (refunds, terminal charges, till sales)
+// protected even if a route is ever re-registered on a non-admin router (S-1).
+func isAdminRequest(r *http.Request) bool {
+	role, ok := r.Context().Value(mw.UserRoleKey).(string)
+	return ok && role == "admin"
+}
+
 // GetDiscountPreviewHandler returns eligible discounts for a booking without applying them.
 // GET /api/bookings/{id}/discount-preview
 func GetDiscountPreviewHandler(w http.ResponseWriter, r *http.Request) {
@@ -314,6 +328,12 @@ func calculateDiscountPreview(ctx context.Context, bookingID string, userID stri
 }
 
 func CreateTerminalPayment(w http.ResponseWriter, r *http.Request) {
+	// Defense-in-depth admin check (S-1) — the route is mounted under
+	// mw.RequireAdmin; this keeps terminal charges admin-only regardless.
+	if !isAdminRequest(r) {
+		http.Error(w, "Admin access required", http.StatusForbidden)
+		return
+	}
 	bookingID := chi.URLParam(r, "id")
 	if bookingID == "" || !validators.IsValidID(bookingID) {
 		http.Error(w, "Booking not found", http.StatusNotFound)
@@ -339,9 +359,6 @@ func CreateTerminalPayment(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	// M8
-	// L5
-
 	if err := ValidateAmount(req.Amount); err != nil {
 		log.Printf("Failed to process request: %v", err)
 		http.Error(w, "Invalid request", http.StatusBadRequest)
@@ -561,6 +578,199 @@ func CreateTerminalPayment(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	// Admin "Charge Saved Card": charge the customer's saved card directly via
+	// Square (no terminal). Pending-first with full idempotency: a deterministic
+	// key derived from booking+type+amount+card means a network retry reuses the
+	// same key — Square dedups the charge and the pending record is resumed, so
+	// a lost-response retry can NEVER double-charge. Mirrors CreateTipPayment.
+	if req.PaymentMethod != nil && *req.PaymentMethod == "saved_card" {
+		if req.UserSavedCardID == nil || *req.UserSavedCardID == "" {
+			http.Error(w, "saved_card_id is required for saved_card payment", http.StatusBadRequest)
+			return
+		}
+
+		status, err := service.GetBookingStatus(r.Context(), bookingID)
+		if err != nil {
+			if errors.Is(err, pgx.ErrNoRows) {
+				http.Error(w, "Booking not found", http.StatusNotFound)
+				return
+			}
+			log.Printf("Failed to get booking status: %v", err)
+			http.Error(w, "internal server error", http.StatusInternalServerError)
+			return
+		}
+		if status != "in_progress" && status != "completed" {
+			http.Error(w, "Booking must be in_progress or completed to create payment", http.StatusBadRequest)
+			return
+		}
+
+		// The saved card is owned by the booking's user, not the admin.
+		var bookingUserID sql.NullString
+		if err := db.Conn.QueryRow(r.Context(), `SELECT user_id FROM bookings WHERE id = $1`, bookingID).Scan(&bookingUserID); err != nil {
+			log.Printf("Failed to get booking user: %v", err)
+			http.Error(w, "internal server error", http.StatusInternalServerError)
+			return
+		}
+		card, err := service.GetCardByID(r.Context(), *req.UserSavedCardID, bookingUserID.String)
+		if err != nil {
+			if errors.Is(err, pgx.ErrNoRows) {
+				http.Error(w, "Saved card not found", http.StatusNotFound)
+				return
+			}
+			log.Printf("Failed to get saved card: %v", err)
+			http.Error(w, "internal server error", http.StatusInternalServerError)
+			return
+		}
+
+		// Serialize saved-card charges per booking (same lock as online booking
+		// payments) so concurrent double-clicks can't both pass the idempotency
+		// check. Mirrors the CreateBookingPayment lock (R4).
+		pinConn, err := db.Conn.Acquire(r.Context())
+		if err != nil {
+			log.Printf("Failed to acquire connection for saved-card lock: %v", err)
+			http.Error(w, "internal server error", http.StatusInternalServerError)
+			return
+		}
+		defer pinConn.Release()
+		if _, err := pinConn.Exec(r.Context(), `
+			SELECT pg_advisory_lock(hashtext('crussell:payment:' || $1))
+		`, bookingID); err != nil {
+			log.Printf("Failed to acquire saved-card serialization lock for %s: %v", bookingID, err)
+			http.Error(w, "internal server error", http.StatusInternalServerError)
+			return
+		}
+		defer func() {
+			if _, err := pinConn.Exec(context.Background(), `
+				SELECT pg_advisory_unlock(hashtext('crussell:payment:' || $1))
+			`, bookingID); err != nil {
+				log.Printf("Failed to release saved-card serialization lock for %s: %v", bookingID, err)
+			}
+		}()
+
+		// Deterministic idempotency key: booking+type+amount+card. A network
+		// retry with the same inputs derives the same key → dedup, never a
+		// second charge. ≤45 chars for Square's limit.
+		scKey := bookingID + "-sc-" + req.PaymentType + "-" + strconv.FormatInt(amount, 10) + "-" + *req.UserSavedCardID
+
+		// Idempotency switch inside the lock: completed → dedup; pending →
+		// reuse (re-attempt Square with the same key, which dedups Square-side);
+		// failed → clean rejection.
+		var existingID, existingStatus sql.NullString
+		var existingAmount sql.NullFloat64
+		err = db.Conn.QueryRow(r.Context(), `
+			SELECT id, status, amount FROM payments WHERE booking_id = $1 AND idempotency_key = $2
+		`, bookingID, scKey).Scan(&existingID, &existingStatus, &existingAmount)
+
+		paymentID := ""
+		switch {
+		case err == nil && existingStatus.String == "completed":
+			// Dedup — return the existing completed payment.
+			if err := json.NewEncoder(w).Encode(CheckoutResponse{
+				CheckoutID: existingID.String,
+				Status:     "COMPLETED",
+			}); err != nil {
+				log.Printf("Failed to encode JSON response: %v", err)
+			}
+			return
+		case err == nil && existingStatus.String == "pending":
+			// Reuse the pending record: a prior attempt's Square outcome is
+			// unknown. Guard the amount — a retry with a different amount must
+			// not reuse the old record's charge.
+			if int64(math.Round(existingAmount.Float64*100)) != amount {
+				log.Printf("Saved-card retry amount mismatch: pending %s has %d pence, request has %d pence", existingID.String, int64(math.Round(existingAmount.Float64*100)), amount)
+				http.Error(w, "Amount does not match the pending payment", http.StatusBadRequest)
+				return
+			}
+			paymentID = existingID.String
+		case err == nil && existingStatus.String == "failed":
+			log.Printf("Saved-card payment %s was previously marked failed (swept) — refusing retry", existingID.String)
+			http.Error(w, "This payment previously failed and can no longer be retried", http.StatusConflict)
+			return
+		case err != nil && !errors.Is(err, pgx.ErrNoRows):
+			log.Printf("Failed to check saved-card idempotency: %v", err)
+			http.Error(w, "internal server error", http.StatusInternalServerError)
+			return
+		}
+
+		// Pending-first: insert a pending payment record, commit, then charge.
+		tx, err := db.Conn.Begin(r.Context())
+		if err != nil {
+			log.Printf("Failed to begin transaction: %v", err)
+			http.Error(w, "internal server error", http.StatusInternalServerError)
+			return
+		}
+		if paymentID == "" {
+			record := PaymentRecord{
+				BookingID:       bookingID,
+				PaymentType:     req.PaymentType,
+				PaymentMethod:   "online_square",
+				Status:          "pending",
+				Amount:          float64(amount) / 100.0,
+				IdempotencyKey:  &scKey,
+				UserSavedCardID: req.UserSavedCardID,
+				CreatedAt:       clock.Now(),
+				UpdatedAt:       clock.Now(),
+				CreatedBy:       &adminID,
+			}
+			if err := tx.QueryRow(r.Context(), `
+				INSERT INTO payments (booking_id, payment_type, payment_method, status, amount, idempotency_key, user_saved_card_id, created_by, created_at, updated_at)
+				VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10)
+				RETURNING id
+			`, record.BookingID, record.PaymentType, record.PaymentMethod, record.Status, record.Amount, record.IdempotencyKey, record.UserSavedCardID, record.CreatedBy, record.CreatedAt, record.UpdatedAt).Scan(&paymentID); err != nil {
+				log.Printf("Failed to insert pending saved-card payment: %v", err)
+				_ = tx.Rollback(r.Context())
+				http.Error(w, "internal server error", http.StatusInternalServerError)
+				return
+			}
+		}
+		if err := tx.Commit(r.Context()); err != nil {
+			log.Printf("Failed to commit pending saved-card payment: %v", err)
+			http.Error(w, "internal server error", http.StatusInternalServerError)
+			return
+		}
+
+		var buyerEmail string
+		if bookingUserID.Valid {
+			_ = db.Conn.QueryRow(r.Context(), `SELECT email FROM users WHERE id = $1`, bookingUserID.String).Scan(&buyerEmail)
+		}
+
+		paymentResult, err := SquareClient.CreatePayment(r.Context(), square.CreatePaymentReq{
+			Amount:         amount,
+			Currency:       "GBP",
+			SourceID:       card.SquareCardID,
+			IdempotencyKey: scKey,
+			ReferenceID:    bookingID,
+			Note:           req.PaymentType,
+			BuyerEmail:     buyerEmail,
+		})
+		if err != nil {
+			log.Printf("Failed to process saved-card payment: %v", err)
+			http.Error(w, "Payment failed", http.StatusPaymentRequired)
+			return
+		}
+
+		if _, upErr := db.Conn.Exec(r.Context(),
+			`UPDATE payments SET status = 'completed', square_payment_id = $1 WHERE id = $2`,
+			paymentResult.SquarePayID, paymentID,
+		); upErr != nil {
+			log.Printf("CRITICAL: Square payment %s succeeded but saved-card payment %s update failed: %v — manual reconciliation required", paymentResult.SquarePayID, paymentID, upErr)
+			http.Error(w, "internal server error", http.StatusInternalServerError)
+			return
+		}
+
+		// Return the card details the frontend reads for the success state
+		// (MINOR-R2) — CheckoutResponse alone leaves card_brand/card_last4 blank.
+		if err := json.NewEncoder(w).Encode(map[string]any{
+			"checkout_id": paymentID,
+			"status":      "COMPLETED",
+			"card_brand":  paymentResult.CardBrand,
+			"card_last4":  paymentResult.CardLast4,
+		}); err != nil {
+			log.Printf("Failed to encode JSON response: %v", err)
+		}
+		return
+	}
+
 	// For Square checkout (terminal card reader), validate booking status
 	// and check idempotency. No DB transaction needed since Square handles
 	// the payment — no DB writes occur until GetCheckoutStatus.
@@ -617,12 +827,18 @@ func CreateTerminalPayment(w http.ResponseWriter, r *http.Request) {
 }
 
 func GetCheckoutStatus(w http.ResponseWriter, r *http.Request) {
+	// Defense-in-depth admin check (S-1) — terminal completion records a
+	// payment, so it must stay admin-only.
+	if !isAdminRequest(r) {
+		http.Error(w, "Admin access required", http.StatusForbidden)
+		return
+	}
 	checkoutID := chi.URLParam(r, "checkout_id")
 	if checkoutID == "" {
 		http.Error(w, "Checkout ID is required", http.StatusBadRequest)
 		return
 	}
-	if !validators.IsValidID(checkoutID) {
+	if !validators.IsValidSquareCheckoutID(checkoutID) {
 		http.Error(w, "not found", http.StatusNotFound)
 		return
 	}
@@ -650,6 +866,17 @@ func GetCheckoutStatus(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	// Ownership check: the terminal checkout must reference THIS booking.
+	// CreateTerminalPayment sets reference_id = bookingID; without this check,
+	// polling the wrong checkout ID would attach its payment to a different
+	// booking (admin-only route, but a mis-scoped charge is a data-integrity
+	// bug worth rejecting).
+	if paymentResult.ReferenceID != "" && paymentResult.ReferenceID != bookingID {
+		log.Printf("Checkout %s references booking %s, not %s — refusing to record", checkoutID, paymentResult.ReferenceID, bookingID)
+		http.Error(w, "Checkout does not belong to this booking", http.StatusBadRequest)
+		return
+	}
+
 	if paymentResult.Status == "COMPLETED" {
 		service := NewPaymentService()
 
@@ -813,9 +1040,6 @@ func CreateBookingPayment(w http.ResponseWriter, r *http.Request) {
 		log.Printf("[SQUARE-PROD] Failed to resolve buyer email for user %s: %v (Square receipts will not be emailed)", userID, err)
 	}
 
-	// M8
-	// L5
-
 	if err := ValidateAmount(req.Amount); err != nil {
 		log.Printf("Failed to process request: %v", err)
 		http.Error(w, "Invalid request", http.StatusBadRequest)
@@ -937,17 +1161,29 @@ func CreateBookingPayment(w http.ResponseWriter, r *http.Request) {
 	}
 
 	// Check idempotency inside the transaction.
+	// Only short-circuit when the existing record is 'completed'. A 'pending'
+	// record means the previous Square call failed — returning it as 200 would
+	// show a success toast without ever charging. Re-attempt the charge below
+	// with the same idempotency key (Square dedups safely) and reuse the
+	// existing record. This mirrors CreateTipPayment exactly.
 	var existingID sql.NullString
 	var existingBookingID sql.NullString
 	var existingPaymentType sql.NullString
 	var existingStatus sql.NullString
 	var existingAmount sql.NullFloat64
 	var existingCreatedAt sql.NullTime
-	if err := tx.QueryRow(r.Context(), `
+
+	err = tx.QueryRow(r.Context(), `
 		SELECT id, booking_id, payment_type, status, amount, created_at
 		FROM payments
 		WHERE booking_id = $1 AND idempotency_key = $2
-	`, bookingID, req.IdempotencyKey).Scan(&existingID, &existingBookingID, &existingPaymentType, &existingStatus, &existingAmount, &existingCreatedAt); err == nil {
+	`, bookingID, req.IdempotencyKey).Scan(&existingID, &existingBookingID, &existingPaymentType, &existingStatus, &existingAmount, &existingCreatedAt)
+
+	paymentID := ""
+	reusePendingRecord := false
+	switch {
+	case err == nil && existingStatus.String == "completed":
+		// Idempotent dedup — return the already-completed payment.
 		if err := json.NewEncoder(w).Encode(PaymentResponse{
 			ID:          existingID.String,
 			BookingID:   existingBookingID.String,
@@ -959,7 +1195,27 @@ func CreateBookingPayment(w http.ResponseWriter, r *http.Request) {
 			log.Printf("Failed to encode JSON response: %v", err)
 		}
 		return
-	} else if !errors.Is(err, pgx.ErrNoRows) {
+	case err == nil && existingStatus.String == "pending":
+		// Previous Square call failed — reuse the pending record and re-attempt.
+		// Guard the amount: a retry with a different amount must not mutate the
+		// original record or charge the new amount against the old key. Compare
+		// in pence via math.Round — int64(pounds*100) truncation would reject
+		// legitimate same-amount retries for non-exact values (see CreateTipPayment).
+		if int64(math.Round(existingAmount.Float64*100)) != req.Amount {
+			log.Printf("Payment retry amount mismatch: pending record %s has %d pence, request has %d pence", existingID.String, int64(math.Round(existingAmount.Float64*100)), req.Amount)
+			http.Error(w, "Amount does not match the pending payment", http.StatusBadRequest)
+			return
+		}
+		paymentID = existingID.String
+		reusePendingRecord = true
+	case err == nil && existingStatus.String == "failed":
+		// Swept as stale (>24h) or definitively rejected — a retry would risk a
+		// second Square charge. Reject cleanly instead of 500-ing on the
+		// idempotency_key UNIQUE constraint (R2).
+		log.Printf("Payment retry rejected: record %s was marked failed", existingID.String)
+		http.Error(w, "This payment previously failed and can no longer be retried", http.StatusConflict)
+		return
+	case err != nil && !errors.Is(err, pgx.ErrNoRows):
 		log.Printf("Failed to check idempotency: %v", err)
 	}
 
@@ -1032,6 +1288,53 @@ func CreateBookingPayment(w http.ResponseWriter, r *http.Request) {
 		savedCardID = req.CardID
 	}
 
+	// If there is no pending record to reuse, insert one NOW and commit the
+	// transaction BEFORE calling Square. The committed pending row binds the
+	// idempotency key in the DB, so a post-charge insert/commit failure leaves
+	// a retryable pending record instead of an unbound key (a same-key retry
+	// would otherwise re-charge). It also releases the DB transaction before
+	// the ~30s Square round-trip instead of holding it open across the call.
+	if !reusePendingRecord {
+		fees := service.CalculateFees(req.Amount, "online")
+		pendingRecord := PaymentRecord{
+			BookingID:       bookingID,
+			PaymentType:     req.PaymentType,
+			PaymentMethod:   "online_square",
+			Status:          "pending",
+			Amount:          float64(req.Amount) / 100.0,
+			IdempotencyKey:  &req.IdempotencyKey,
+			Fees:            float64(fees) / 100.0,
+			UserSavedCardID: savedCardID,
+			CreatedAt:       clock.Now(),
+			UpdatedAt:       clock.Now(),
+			CreatedBy:       &userID,
+		}
+		paymentID, err = service.CreatePaymentRecordTx(r.Context(), tx, pendingRecord, nil)
+		if err != nil {
+			log.Printf("Failed to create pending payment record: %v", err)
+			http.Error(w, "internal server error", http.StatusInternalServerError)
+			return
+		}
+		// Apply VAT to the pending record inside the same transaction — same
+		// pattern as CreateTipPayment.
+		ApplyVATToBookingPayment(r.Context(), tx, paymentID)
+	}
+
+	// Always commit the transaction. In the reuse path no rows were written,
+	// but the commit is required in the test harness: there the context carries
+	// an outer test tx, so Begin creates a nested savepoint whose deferred
+	// rollback would otherwise undo the post-charge UPDATE executed later on
+	// the same connection. In production Begin is a plain tx and this commit is
+	// a harmless no-op that keeps both paths identical.
+	if err := tx.Commit(r.Context()); err != nil {
+		log.Printf("Failed to commit transaction: %v", err)
+		http.Error(w, "internal server error", http.StatusInternalServerError)
+		return
+	}
+
+	// Step 2: DB transaction committed — safe to call Square now. If Square
+	// fails, the record stays 'pending' and a same-key retry reuses it.
+
 	paymentReq := square.CreatePaymentReq{
 		Amount:         req.Amount,
 		Currency:       "GBP",
@@ -1049,15 +1352,32 @@ func CreateBookingPayment(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	fees := service.CalculateFees(req.Amount, "online")
-
 	paymentAmount := float64(req.Amount) / 100.0
 
+	// Step 3: Square succeeded — record the completed payment state in a NEW
+	// transaction (split records, VAT, deposit promotion, campaigns). The
+	// pending row committed in step 1 already holds the primary idempotency
+	// key, so it IS the primary record: update it to 'completed' with the
+	// Square payment ID, then insert only the additional -split-N records.
+	tx2, txErr := db.Conn.Begin(r.Context())
+	if txErr != nil {
+		log.Printf("CRITICAL: Square payment %s (ID=%s) was processed but opening the post-charge transaction failed: %v — manual reconciliation required",
+			paymentResult.Status, paymentResult.SquarePayID, txErr)
+		http.Error(w, "internal server error", http.StatusInternalServerError)
+		return
+	}
+	defer func() {
+		if err := tx2.Rollback(r.Context()); err != nil && !errors.Is(err, pgx.ErrTxClosed) {
+			slog.Error("failed to rollback post-charge transaction", "err", err)
+		}
+	}()
+
 	// Build payment records — may split a single Square charge into
 	// a deposit portion (up to 50% of booking total) plus a balance
 	// portion, so the refund system can correctly track deposit vs
 	// non-deposit money per the deposit protection policy.
 	bookingInfo, bErr := service.GetBookingPaymentInfo(r.Context(), bookingID)
+	fees := service.CalculateFees(req.Amount, "online")
 	primaryRecord := PaymentRecord{
 		BookingID:       bookingID,
 		PaymentType:     req.PaymentType,
@@ -1083,41 +1403,62 @@ func CreateBookingPayment(w http.ResponseWriter, r *http.Request) {
 		records = []PaymentRecord{primaryRecord}
 	}
 
-	// Create all payment records for this Square charge inside the transaction
-	// so that if any insert fails the entire group rolls back. This prevents
-	// a data inconsistency where Square charged the customer but only part of
-	// the split is reflected in the DB.
+	// The primary split record (records[0]) is the committed pending row. Its
+	// amount/payment_type may differ from the pending insert (deposit carving
+	// in buildSplitRecords), so align the row to the computed values. The VAT
+	// fields are cleared so apply_vat_to_payment recomputes on the final amount
+	// — the pending record had VAT applied at the pre-split amount.
+	primary := records[0]
+	if _, upErr := tx2.Exec(r.Context(), `
+		UPDATE payments SET
+			status = 'completed',
+			square_payment_id = $1,
+			amount = $2,
+			payment_type = $3,
+			fees = $4,
+			is_vat_applicable = FALSE,
+			vat_rate = NULL,
+			vat_amount = NULL,
+			net_amount = NULL,
+			updated_at = NOW()
+		WHERE id = $5
+	`, paymentResult.SquarePayID, primary.Amount, primary.PaymentType, primary.Fees, paymentID); upErr != nil {
+		log.Printf("CRITICAL: Square payment %s (ID=%s) was processed but updating payment %s to completed failed: %v — manual reconciliation required",
+			paymentResult.Status, paymentResult.SquarePayID, paymentID, upErr)
+		http.Error(w, "internal server error", http.StatusInternalServerError)
+		return
+	}
 
-	var primaryPaymentID string
+	// Insert the additional split records. They carry the derived -split-N
+	// idempotency keys, which are new rows; if the split produced only one
+	// record, there is nothing more to insert.
 	var paymentIDs []string
-	for i, rec := range records {
-		pid, cErr := service.CreatePaymentRecordTx(r.Context(), tx, rec, nil)
+	for i, rec := range records[1:] {
+		pid, cErr := service.CreatePaymentRecordTx(r.Context(), tx2, rec, nil)
 		if cErr != nil {
-			log.Printf("Failed to create payment record %d/%d: %v", i+1, len(records), cErr)
+			log.Printf("Failed to create split payment record %d/%d: %v", i+2, len(records), cErr)
 			http.Error(w, "internal server error", http.StatusInternalServerError)
 			return
 		}
 		paymentIDs = append(paymentIDs, pid)
-		if i == 0 {
-			primaryPaymentID = pid
-		}
 	}
 
 	// Apply VAT to all split records if the business is VAT-registered.
 	// Must be inside the transaction so VAT updates are atomic with inserts.
-	vatCfg, vatErr := GetVATConfig(r.Context(), tx)
+	vatCfg, vatErr := GetVATConfig(r.Context(), tx2)
 	if vatErr == nil && vatCfg.IsVATRegistered {
-		for _, pid := range paymentIDs {
-			if _, execErr := tx.Exec(r.Context(), "SELECT apply_vat_to_payment($1, $2)", pid, vatCfg.DefaultVATRate); execErr != nil {
+		vatIDs := append([]string{paymentID}, paymentIDs...)
+		for _, pid := range vatIDs {
+			if _, execErr := tx2.Exec(r.Context(), "SELECT apply_vat_to_payment($1, $2)", pid, vatCfg.DefaultVATRate); execErr != nil {
 				log.Printf("Failed to apply VAT to payment %s: %v", pid, execErr)
 			}
 		}
 	}
 
 	// Promote deposit to confirmed if total paid meets the 20% threshold.
-	// Check is inside the transaction so it sees the just-inserted payments.
+	// Check is inside the transaction so it sees the just-completed primary.
 	var depositMet bool
-	if err := tx.QueryRow(r.Context(), `
+	if err := tx2.QueryRow(r.Context(), `
 		WITH booking_total AS (
 			SELECT total_amount * 100 AS total_cents FROM bookings WHERE id = $1
 		),
@@ -1133,7 +1474,7 @@ func CreateBookingPayment(w http.ResponseWriter, r *http.Request) {
 	}
 
 	if depositMet {
-		if _, err := tx.Exec(r.Context(), `
+		if _, err := tx2.Exec(r.Context(), `
 			UPDATE bookings SET status = 'confirmed', updated_at = NOW()
 			WHERE id = $1 AND status = 'pending_release'
 		`, bookingID); err != nil {
@@ -1144,9 +1485,9 @@ func CreateBookingPayment(w http.ResponseWriter, r *http.Request) {
 	// Apply eligible campaign discounts inside the payment transaction, so
 	// atomicity with the payment inserts is guaranteed. The call is idempotent
 	// — if discounts were already applied, the duplicate check skips them.
-	applyEligibleCampaignsAtPayment(r.Context(), tx, bookingID, userID)
+	applyEligibleCampaignsAtPayment(r.Context(), tx2, bookingID, userID)
 
-	if cErr := tx.Commit(r.Context()); cErr != nil {
+	if cErr := tx2.Commit(r.Context()); cErr != nil {
 		log.Printf("CRITICAL: Square payment %s (ID=%s) was processed but DB transaction commit failed: %v — manual reconciliation required",
 			paymentResult.Status, paymentResult.SquarePayID, cErr)
 		http.Error(w, "internal server error", http.StatusInternalServerError)
@@ -1154,7 +1495,7 @@ func CreateBookingPayment(w http.ResponseWriter, r *http.Request) {
 	}
 
 	if err := json.NewEncoder(w).Encode(PaymentResponse{
-		ID:          primaryPaymentID,
+		ID:          paymentID,
 		BookingID:   bookingID,
 		PaymentType: req.PaymentType,
 		Status:      "completed",
@@ -1560,6 +1901,12 @@ func GetUserPaymentMethods(w http.ResponseWriter, r *http.Request) {
 }
 
 func AdminGetUserPaymentMethods(w http.ResponseWriter, r *http.Request) {
+	// Defense-in-depth admin check (S-1) — exposing another user's saved cards
+	// must stay admin-only.
+	if !isAdminRequest(r) {
+		http.Error(w, "Admin access required", http.StatusForbidden)
+		return
+	}
 	userID := chi.URLParam(r, "id")
 	if userID == "" || !validators.IsValidID(userID) {
 		http.Error(w, "Invalid user ID", http.StatusBadRequest)
@@ -1652,6 +1999,13 @@ func CreatePaymentMethod(w http.ResponseWriter, r *http.Request) {
 }
 
 func RefundPayment(w http.ResponseWriter, r *http.Request) {
+	// Defense-in-depth: the route is mounted under mw.RequireAdmin, but this
+	// in-handler check keeps refund access admin-only even if the route is ever
+	// re-registered on a non-admin router (S-1).
+	if !isAdminRequest(r) {
+		http.Error(w, "Admin access required", http.StatusForbidden)
+		return
+	}
 	paymentID := chi.URLParam(r, "payment_id")
 	if paymentID == "" || !validators.IsValidID(paymentID) {
 		http.Error(w, "Payment not found", http.StatusNotFound)
@@ -1710,10 +2064,15 @@ func RefundPayment(w http.ResponseWriter, r *http.Request) {
 	// does not create a second Square refund. When the client supplies an
 	// idempotency key (one per distinct refund attempt, reused on retry), use
 	// it — the amount-derived fallback would collide on two DISTINCT partial
-	// refunds of the same amount, silently swallowing the second.
+	// refunds of the same amount, silently swallowing the second. The client
+	// key is hashed+truncated: Square's idempotency-key limit is 45 chars, and
+	// paymentID (12) + "-refund-" (8) + a full 36-char UUID (56 total) would
+	// be rejected with a 400. The hash stays deterministic, so a same-key
+	// retry still dedups.
 	idempotencyKey := paymentID + "-refund-" + strconv.FormatInt(req.Amount, 10)
 	if req.IdempotencyKey != "" {
-		idempotencyKey = paymentID + "-refund-" + req.IdempotencyKey
+		ikHash := sha256.Sum256([]byte(req.IdempotencyKey))
+		idempotencyKey = paymentID + "-refund-" + fmt.Sprintf("%x", ikHash)[:24]
 	}
 
 	// Serialize refund attempts per payment to prevent two concurrent refunds
@@ -1824,9 +2183,19 @@ func RefundPayment(w http.ResponseWriter, r *http.Request) {
 			reissueResult, reissueErr := SquareClient.RefundPayment(r.Context(), reissueReq)
 			switch {
 			case reissueErr == nil:
+				// Resolve by Square's status: PENDING stays pending (sweep
+				// reconciles), FAILED/REJECTED is definitive, COMPLETED resolves.
+				reissueStatus := "completed"
+				if reissueResult.Status == "PENDING" {
+					reissueStatus = "pending"
+					log.Printf("Square reissue %s is PENDING — leaving refund %s pending for the sweep", reissueResult.ID, existingRefundID.String)
+				} else if reissueResult.Status == "FAILED" || reissueResult.Status == "REJECTED" {
+					reissueStatus = "failed"
+					log.Printf("Square reissue %s FAILED — marking refund %s failed", reissueResult.ID, existingRefundID.String)
+				}
 				if _, upErr := db.Conn.Exec(r.Context(),
-					`UPDATE refunds SET status = 'completed', square_refund_id = $1 WHERE id = $2`,
-					reissueResult.ID, existingRefundID.String,
+					`UPDATE refunds SET status = $1, square_refund_id = $2 WHERE id = $3`,
+					reissueStatus, reissueResult.ID, existingRefundID.String,
 				); upErr != nil {
 					log.Printf("CRITICAL: Square refund committed (%s) but DB update for refund %s failed — manual reconciliation required: %v", reissueResult.ID, existingRefundID.String, upErr)
 					http.Error(w, "internal server error", http.StatusInternalServerError)
@@ -1836,7 +2205,7 @@ func RefundPayment(w http.ResponseWriter, r *http.Request) {
 					ID:        existingRefundID.String,
 					PaymentID: paymentID,
 					Amount:    req.Amount,
-					Status:    "completed",
+					Status:    reissueStatus,
 					Reason:    req.Reason,
 					CreatedAt: clock.Now().Format(time.RFC3339),
 				}); err != nil {
@@ -1972,13 +2341,20 @@ func RefundPayment(w http.ResponseWriter, r *http.Request) {
 	}()
 
 	var refundID string
+	// booking_id is NULL for non-booking payments (gift-card purchase refunds);
+	// payments without a booking leave it NULL rather than inserting an empty
+	// string that violates the refunds.booking_id FK/NOT NULL.
+	var refundBookingID any = payment.BookingID
+	if payment.BookingID == "" {
+		refundBookingID = nil
+	}
 	err = tx.QueryRow(r.Context(), `
 		INSERT INTO refunds (payment_id, booking_id, amount, status, reason, idempotency_key, created_by, created_at, origin)
 		VALUES ($1, $2, $3, 'pending', $4, $5, $6, $7, 'manual')
 		RETURNING id
 	`,
 		paymentID,
-		payment.BookingID,
+		refundBookingID,
 		float64(req.Amount)/100.0,
 		req.Reason,
 		idempotencyKey,
@@ -2044,14 +2420,26 @@ func RefundPayment(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	squareRefundID := refundResult.ID
+	// Square succeeded — resolve the refund row by Square's status. A
+	// synchronous refund response can be PENDING (money in flight, e.g. an
+	// async card network): marking it completed while Square later fails it
+	// would permanently block that amount in the over-refund guard. Only a
+	// definitive COMPLETED resolves to completed; PENDING stays pending for the
+	// sweep to reconcile; FAILED/REJECTED is a real failure.
+	status := "completed"
+	if refundResult.Status == "PENDING" {
+		status = "pending"
+		log.Printf("Square refund %s is PENDING (in flight) — leaving refund %s pending for the sweep to resolve", refundResult.ID, refundID)
+	} else if refundResult.Status == "FAILED" || refundResult.Status == "REJECTED" {
+		status = "failed"
+		log.Printf("Square refund %s FAILED — marking refund %s failed", refundResult.ID, refundID)
+	}
 
-	// Square succeeded — update the refund record to completed.
 	if _, upErr := db.Conn.Exec(r.Context(),
-		`UPDATE refunds SET status = 'completed', square_refund_id = $1 WHERE id = $2`,
-		squareRefundID, refundID,
+		`UPDATE refunds SET status = $1, square_refund_id = $2 WHERE id = $3`,
+		status, refundResult.ID, refundID,
 	); upErr != nil {
-		log.Printf("CRITICAL: Square refund committed (%s) but DB update for refund %s failed — manual reconciliation required: %v", squareRefundID, refundID, upErr)
+		log.Printf("CRITICAL: Square refund committed (%s) but DB update for refund %s failed — manual reconciliation required: %v", refundResult.ID, refundID, upErr)
 		http.Error(w, "internal server error", http.StatusInternalServerError)
 		return
 	}
@@ -2060,7 +2448,7 @@ func RefundPayment(w http.ResponseWriter, r *http.Request) {
 		ID:        refundID,
 		PaymentID: paymentID,
 		Amount:    req.Amount,
-		Status:    "completed",
+		Status:    status,
 		Reason:    req.Reason,
 		CreatedAt: clock.Now().Format(time.RFC3339),
 	}); err != nil {
@@ -2119,9 +2507,21 @@ func resumeManualPendingRefund(w http.ResponseWriter, r *http.Request, paymentID
 		http.Error(w, "Refund failed", http.StatusInternalServerError)
 		return
 	}
+	// Resolve by Square's status — a PENDING resume stays pending for the
+	// sweep (marking it completed while Square later fails it would block the
+	// amount in the over-refund guard forever); FAILED/REJECTED is definitive.
+	status := "completed"
+	if resumeResult.Status == "PENDING" {
+		status = "pending"
+		log.Printf("Square refund %s is PENDING — leaving refund %s pending for the sweep", resumeResult.ID, refundID)
+	} else if resumeResult.Status == "FAILED" || resumeResult.Status == "REJECTED" {
+		status = "failed"
+		log.Printf("Square refund %s FAILED — marking refund %s failed", resumeResult.ID, refundID)
+	}
+
 	if _, upErr := db.Conn.Exec(r.Context(),
-		`UPDATE refunds SET status = 'completed', square_refund_id = $1 WHERE id = $2`,
-		resumeResult.ID, refundID,
+		`UPDATE refunds SET status = $1, square_refund_id = $2 WHERE id = $3`,
+		status, resumeResult.ID, refundID,
 	); upErr != nil {
 		log.Printf("CRITICAL: Square refund committed (%s) but DB update for refund %s failed — manual reconciliation required: %v", resumeResult.ID, refundID, upErr)
 		http.Error(w, "internal server error", http.StatusInternalServerError)
@@ -2131,7 +2531,7 @@ func resumeManualPendingRefund(w http.ResponseWriter, r *http.Request, paymentID
 		ID:        refundID,
 		PaymentID: paymentID,
 		Amount:    resumeAmount,
-		Status:    "completed",
+		Status:    status,
 		Reason:    refundReason,
 		CreatedAt: clock.Now().Format(time.RFC3339),
 	}); err != nil {
@@ -2352,6 +2752,14 @@ func CreateTipPayment(w http.ResponseWriter, r *http.Request) {
 		}
 		paymentID = existingID.String
 		reusePendingRecord = true
+	case err == nil && existingStatus.String == "failed":
+		// Swept as stale (>24h, past Square's key retention) or definitively
+		// rejected. A retry can no longer be replayed against Square without
+		// risking a second charge — reject cleanly instead of inserting a new
+		// pending row that 500s on the idempotency_key UNIQUE constraint (R2).
+		log.Printf("Tip retry rejected: pending record %s was marked failed", existingID.String)
+		http.Error(w, "This tip payment previously failed and can no longer be retried", http.StatusConflict)
+		return
 	case err != nil && !errors.Is(err, pgx.ErrNoRows):
 		log.Printf("Failed to check tip idempotency: %v", err)
 	}
diff --git a/backend/handlers/payments/loyalty.go b/backend/handlers/payments/loyalty.go
index d6af1b4..5d547f2 100644
--- a/backend/handlers/payments/loyalty.go
+++ b/backend/handlers/payments/loyalty.go
@@ -1,6 +1,7 @@
 package payments
 
 import (
+	"context"
 	"crussell/db"
 	"crussell/internal/validators"
 	"crussell/mw"
@@ -83,6 +84,34 @@ func ApplyLoyaltyRedemption(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	// Serialize redemption per booking: two concurrent redemptions could both
+	// pass the checks above and both insert a discount (double-apply). Reuse
+	// the booking-payment advisory lock so redemption is mutually exclusive
+	// with payments and other redemptions on the same booking (N-6).
+	pinConn, err := db.Conn.Acquire(r.Context())
+	if err != nil {
+		log.Printf("Failed to acquire connection for loyalty redemption lock: %v", err)
+		http.Error(w, "internal server error", http.StatusInternalServerError)
+		return
+	}
+	defer pinConn.Release()
+	if _, err := pinConn.Exec(r.Context(), `
+		SELECT pg_advisory_lock(hashtext('crussell:payment:' || $1))
+	`, bookingID); err != nil {
+		log.Printf("Failed to acquire loyalty redemption serialization lock for %s: %v", bookingID, err)
+		http.Error(w, "internal server error", http.StatusInternalServerError)
+		return
+	}
+	defer func() {
+		if _, err := pinConn.Exec(context.Background(), `
+			SELECT pg_advisory_unlock(hashtext('crussell:payment:' || $1))
+		`, bookingID); err != nil {
+			log.Printf("Failed to release loyalty redemption serialization lock for %s: %v", bookingID, err)
+		}
+	}()
+
+	// Re-check inside the lock (the checks above ran before acquiring it) so a
+	// concurrent redemption that completed while we waited is caught.
 	var existingDiscount int
 	if err := db.Conn.QueryRow(r.Context(), `
 		SELECT 1 FROM booking_discounts WHERE booking_id = $1 AND discount_source = 'loyalty'
diff --git a/backend/handlers/payments/payments_test.go b/backend/handlers/payments/payments_test.go
index fcde487..7171831 100644
--- a/backend/handlers/payments/payments_test.go
+++ b/backend/handlers/payments/payments_test.go
@@ -31,6 +31,15 @@ func makePaymentRequest(handler http.HandlerFunc, method, path string, body inte
 	return makePaymentAuthRequest(handler, method, path, body, token, "", ctx)
 }
 
+// adminRequestCtx wraps a request context with the admin role so handlers that
+// run a defense-in-depth isAdminRequest check (S-1) work when called directly
+// (bypassing the mw.RequireAdmin middleware that normally injects the role).
+func adminRequestCtx(r *http.Request) *http.Request {
+	reqCtx := context.WithValue(r.Context(), mw.UserRoleKey, "admin")
+	reqCtx = context.WithValue(reqCtx, mw.UserIDKey, "000000000001")
+	return r.WithContext(reqCtx)
+}
+
 func TestValidateCardInfo(t *testing.T) {
 	empty := ""
 	cardID := "card_123"
@@ -2902,6 +2911,7 @@ func TestGetCheckoutStatus_MissingCheckoutID(t *testing.T) {
 	rctx := chi.NewRouteContext()
 	reqCtx := context.WithValue(req.Context(), chi.RouteCtxKey, rctx)
 	req = req.WithContext(reqCtx)
+	req = adminRequestCtx(req)
 
 	w := httptest.NewRecorder()
 	GetCheckoutStatus(w, req)
@@ -2914,13 +2924,18 @@ func TestGetCheckoutStatus_MissingCheckoutID(t *testing.T) {
 func TestGetCheckoutStatus_InvalidCheckoutID(t *testing.T) {
 	_, _ = testutils.SetupTestTx(t)
 
-	req := httptest.NewRequest("GET", "/api/checkout/1234567890abc/status?booking_id=abc", nil)
+	// Must fail the Square-compatible checkout-ID check — the old 12-hex gate
+	// rejected real Square IDs (UUIDs like "08YceKh7B3ZqO"), so an injection
+	// attempt (path traversal) is the correct invalid case now.
+	badID := "../etc/passwd"
+	req := httptest.NewRequest("GET", "/api/checkout/"+badID+"/status?booking_id=abc", nil)
 	rctx := chi.NewRouteContext()
-	rctx.URLParams.Add("checkout_id", "1234567890abc")
+	rctx.URLParams.Add("checkout_id", badID)
 	reqCtx := context.WithValue(req.Context(), chi.RouteCtxKey, rctx)
 	req = req.WithContext(reqCtx)
 
 	w := httptest.NewRecorder()
+	req = adminRequestCtx(req)
 	GetCheckoutStatus(w, req)
 
 	if w.Code != http.StatusNotFound {
@@ -2928,6 +2943,31 @@ func TestGetCheckoutStatus_InvalidCheckoutID(t *testing.T) {
 	}
 }
 
+func TestGetCheckoutStatus_RealSquareID_PassesValidation(t *testing.T) {
+	// A real Square checkout ID (13-char UUID, not 12-hex) must pass the
+	// checkout-ID gate — the C-4 fix. It then 404s at the Square client level
+	// (mock has no such checkout), proving the gate no longer rejects it.
+	_, _ = testutils.SetupTestTx(t)
+
+	realID := "08YceKh7B3ZqO"
+	req := httptest.NewRequest("GET", "/api/checkout/"+realID+"/status?booking_id=abc", nil)
+	rctx := chi.NewRouteContext()
+	rctx.URLParams.Add("checkout_id", realID)
+	reqCtx := context.WithValue(req.Context(), chi.RouteCtxKey, rctx)
+	req = req.WithContext(reqCtx)
+
+	w := httptest.NewRecorder()
+	req = adminRequestCtx(req)
+	GetCheckoutStatus(w, req)
+
+	// Not 404-from-validation: the gate accepted it. The mock returns 500 for
+	// an unknown checkout (it panics on a missing ID), so assert NOT a 404
+	// from the gate — any non-404 is proof the gate passed.
+	if w.Code == http.StatusNotFound {
+		t.Errorf("real Square checkout ID %q was rejected by the validation gate — expected it to pass validation", realID)
+	}
+}
+
 func TestGetCheckoutStatus_ValidCheckoutNotFound(t *testing.T) {
 	_, tx := testutils.SetupTestTx(t)
 
@@ -2951,6 +2991,7 @@ func TestGetCheckoutStatus_ValidCheckoutNotFound(t *testing.T) {
 	req = req.WithContext(reqCtx)
 
 	w := httptest.NewRecorder()
+	req = adminRequestCtx(req)
 	GetCheckoutStatus(w, req)
 
 	if w.Code != http.StatusInternalServerError {
@@ -3011,6 +3052,7 @@ func TestAdminGetUserPaymentMethods_InvalidUserID(t *testing.T) {
 	req = req.WithContext(reqCtx)
 
 	w := httptest.NewRecorder()
+	req = adminRequestCtx(req)
 	AdminGetUserPaymentMethods(w, req)
 
 	if w.Code != http.StatusBadRequest {
@@ -3418,6 +3460,7 @@ func TestGetCheckoutStatus_MissingBookingID(t *testing.T) {
 	req = req.WithContext(reqCtx)
 
 	w := httptest.NewRecorder()
+	req = adminRequestCtx(req)
 	GetCheckoutStatus(w, req)
 
 	if w.Code != http.StatusBadRequest {
@@ -3433,6 +3476,7 @@ func TestGetCheckoutStatus_InvalidBookingID(t *testing.T) {
 	rctx.URLParams.Add("checkout_id", "aaaaaaaaaaaa")
 	reqCtx := context.WithValue(req.Context(), chi.RouteCtxKey, rctx)
 	req = req.WithContext(reqCtx)
+	req = adminRequestCtx(req)
 
 	w := httptest.NewRecorder()
 	GetCheckoutStatus(w, req)
@@ -3452,6 +3496,7 @@ func TestGetCheckoutStatus_BookingNotFound(t *testing.T) {
 	req = req.WithContext(reqCtx)
 
 	w := httptest.NewRecorder()
+	req = adminRequestCtx(req)
 	GetCheckoutStatus(w, req)
 
 	if w.Code != http.StatusInternalServerError {
@@ -3472,8 +3517,10 @@ func TestTerminalPayment_NoAuth(t *testing.T) {
 		PaymentType: "full",
 	}, "", ctx)
 
-	if w.Code != http.StatusUnauthorized {
-		t.Errorf("expected status 401, got %d. body: %s", w.Code, w.Body.String())
+	// No auth token → no role → the defense-in-depth isAdminRequest check
+	// rejects with 403 before the adminID check (S-1).
+	if w.Code != http.StatusForbidden {
+		t.Errorf("expected status 403, got %d. body: %s", w.Code, w.Body.String())
 	}
 }
 
@@ -3538,3 +3585,200 @@ func TestTerminalPayment_ValidatePaymentTypeFails(t *testing.T) {
 }
 
 
+
+func TestSweepStalePendingPayments_MarksOldFailed(t *testing.T) {
+	t.Parallel()
+	ctx, tx := testutils.SetupTestTx(t)
+
+	_, bookingID, _ := setupTestData(t, ctx, tx)
+
+	// A fresh pending payment (should NOT be failed).
+	freshID, err := fixtures.CreateTestPayment(tx, bookingID, 1000.00, "online_square", "full", "pending")
+	if err != nil {
+		t.Fatalf("failed to create fresh pending payment: %v", err)
+	}
+	// A stale pending payment (25h old — past Square's ~24h key retention).
+	staleID, err := fixtures.CreateTestPayment(tx, bookingID, 2000.00, "online_square", "full", "pending")
+	if err != nil {
+		t.Fatalf("failed to create stale pending payment: %v", err)
+	}
+	if _, err := tx.Exec(ctx, "UPDATE payments SET created_at = NOW() - INTERVAL '25 hours' WHERE id = $1", staleID); err != nil {
+		t.Fatalf("failed to age the stale payment: %v", err)
+	}
+
+	_, err = SweepStalePendingPayments(ctx)
+	if err != nil {
+		t.Fatalf("sweep failed: %v", err)
+	}
+
+	// Stale pending → failed; fresh pending untouched.
+	var staleStatus, freshStatus string
+	if err := tx.QueryRow(ctx, "SELECT status FROM payments WHERE id = $1", staleID).Scan(&staleStatus); err != nil {
+		t.Fatalf("failed to query stale payment: %v", err)
+	}
+	if err := tx.QueryRow(ctx, "SELECT status FROM payments WHERE id = $1", freshID).Scan(&freshStatus); err != nil {
+		t.Fatalf("failed to query fresh payment: %v", err)
+	}
+	if staleStatus != "failed" {
+		t.Errorf("expected stale pending payment to be marked failed, got %q", staleStatus)
+	}
+	if freshStatus != "pending" {
+		t.Errorf("expected fresh pending payment to stay pending, got %q", freshStatus)
+	}
+}
+
+// TestSavedCardPayment_LostResponseRetry_Dedups verifies the R1 fix: two
+// "Charge Saved Card" requests with identical inputs (booking + type + amount +
+// card) derive the SAME deterministic idempotency key, so a lost-response
+// retry reuses the completed payment instead of charging twice. Before the fix,
+// every request used a fresh random key → the second click double-charged.
+func TestSavedCardPayment_LostResponseRetry_Dedups(t *testing.T) {
+	t.Parallel()
+	ctx, tx := testutils.SetupTestTx(t)
+
+	userID, bookingID, _ := setupTestData(t, ctx, tx)
+	adminID, err := fixtures.CreateTestAdminUser(tx)
+	if err != nil {
+		t.Fatalf("failed to create admin user: %v", err)
+	}
+	adminToken := jwt.GenerateTestToken(adminID, "admin")
+
+	cardID, err := fixtures.CreateTestPaymentMethod(tx, userID, "ccof:saved-card-test", "VISA", "4242")
+	if err != nil {
+		t.Fatalf("failed to create saved card: %v", err)
+	}
+
+	handler := CreateTerminalPayment
+	reqBody := CreateTerminalPaymentRequest{
+		Amount:          5000,
+		PaymentType:     "full",
+		PaymentMethod:   strPtr("saved_card"),
+		UserSavedCardID: &cardID,
+	}
+
+	// First charge.
+	w1 := makePaymentRequest(handler, "POST", "/api/admin/bookings/"+bookingID+"/payment", reqBody, adminToken, ctx)
+	if w1.Code != http.StatusOK {
+		t.Fatalf("first saved-card charge: expected 200, got %d. body: %s", w1.Code, w1.Body.String())
+	}
+
+	// Same-input retry (lost response) — must dedup, not double-charge.
+	w2 := makePaymentRequest(handler, "POST", "/api/admin/bookings/"+bookingID+"/payment", reqBody, adminToken, ctx)
+	if w2.Code != http.StatusOK {
+		t.Fatalf("retry saved-card charge: expected 200, got %d. body: %s", w2.Code, w2.Body.String())
+	}
+
+	// Exactly ONE payment record for this booking.
+	var payCount int
+	if err := tx.QueryRow(ctx, `SELECT COUNT(*) FROM payments WHERE booking_id = $1 AND payment_method = 'online_square' AND amount = 50.00`, bookingID).Scan(&payCount); err != nil {
+		t.Fatalf("failed to count payments: %v", err)
+	}
+	if payCount != 1 {
+		t.Errorf("expected exactly 1 payment record (dedup), got %d — double-charge!", payCount)
+	}
+}
+
+// TestSavedCardPayment_SweptFailed_Rejected verifies the R2 fix: after the
+// sweep marks a pending payment failed, a same-key retry is cleanly rejected
+// with 409 instead of 500-ing on the idempotency_key UNIQUE constraint.
+func TestSavedCardPayment_SweptFailed_Rejected(t *testing.T) {
+	t.Parallel()
+	ctx, tx := testutils.SetupTestTx(t)
+
+	userID, bookingID, _ := setupTestData(t, ctx, tx)
+	adminID, err := fixtures.CreateTestAdminUser(tx)
+	if err != nil {
+		t.Fatalf("failed to create admin user: %v", err)
+	}
+	adminToken := jwt.GenerateTestToken(adminID, "admin")
+
+	cardID, err := fixtures.CreateTestPaymentMethod(tx, userID, "ccof:swept-card-test", "VISA", "1111")
+	if err != nil {
+		t.Fatalf("failed to create saved card: %v", err)
+	}
+
+	// Seed a failed payment with the deterministic key the handler will derive.
+	scKey := bookingID + "-sc-full-5000-" + cardID
+	if _, err := tx.Exec(ctx, `
+		INSERT INTO payments (booking_id, payment_type, payment_method, status, amount, idempotency_key, user_saved_card_id, created_by, created_at, updated_at)
+		VALUES ($1, 'full', 'online_square', 'failed', 50.00, $2, $3, $4, NOW(), NOW())
+	`, bookingID, scKey, cardID, adminID); err != nil {
+		t.Fatalf("failed to seed failed payment: %v", err)
+	}
+
+	handler := CreateTerminalPayment
+	reqBody := CreateTerminalPaymentRequest{
+		Amount:          5000,
+		PaymentType:     "full",
+		PaymentMethod:   strPtr("saved_card"),
+		UserSavedCardID: &cardID,
+	}
+	w := makePaymentRequest(handler, "POST", "/api/admin/bookings/"+bookingID+"/payment", reqBody, adminToken, ctx)
+	if w.Code != http.StatusConflict {
+		t.Fatalf("expected 409 (swept-failed rejection), got %d. body: %s", w.Code, w.Body.String())
+	}
+
+	// No new payment row was inserted.
+	var payCount int
+	if err := tx.QueryRow(ctx, `SELECT COUNT(*) FROM payments WHERE booking_id = $1 AND idempotency_key = $2`, bookingID, scKey).Scan(&payCount); err != nil {
+		t.Fatalf("failed to count payments: %v", err)
+	}
+	if payCount != 1 {
+		t.Errorf("expected exactly 1 (failed) payment row, got %d", payCount)
+	}
+}
+
+
+// TestSweepStalePendingPayments_CoversTillSales verifies the R3 fix: the sweep
+// also marks stale pending till_sales rows (card payments) as failed, so a
+// lost-response till sale can't stay pending past Square's key retention.
+func TestSweepStalePendingPayments_CoversTillSales(t *testing.T) {
+	t.Parallel()
+	ctx, tx := testutils.SetupTestTx(t)
+
+	adminID, err := fixtures.CreateTestAdminUser(tx)
+	if err != nil {
+		t.Fatalf("failed to create admin user: %v", err)
+	}
+
+	// A stale pending till sale (card payment, 25h old).
+	var tillSaleID string
+	err = tx.QueryRow(ctx, `
+		INSERT INTO till_sales (item_type, description, quantity, unit_price, total_amount, payment_method, status, created_by, created_at, updated_at)
+		VALUES ('gift_card', 'Gift Card create', 1, 50.00, 50.00, 'online_square', 'pending', $1, NOW() - INTERVAL '25 hours', NOW())
+		RETURNING id
+	`, adminID).Scan(&tillSaleID)
+	if err != nil {
+		t.Fatalf("failed to seed pending till sale: %v", err)
+	}
+
+	// A fresh pending till sale that must NOT be swept.
+	var freshSaleID string
+	err = tx.QueryRow(ctx, `
+		INSERT INTO till_sales (item_type, description, quantity, unit_price, total_amount, payment_method, status, created_by, created_at, updated_at)
+		VALUES ('gift_card', 'Gift Card create', 1, 30.00, 30.00, 'online_square', 'pending', $1, NOW(), NOW())
+		RETURNING id
+	`, adminID).Scan(&freshSaleID)
+	if err != nil {
+		t.Fatalf("failed to seed fresh till sale: %v", err)
+	}
+
+	_, err = SweepStalePendingPayments(ctx)
+	if err != nil {
+		t.Fatalf("sweep failed: %v", err)
+	}
+
+	var staleStatus, freshStatus string
+	if err := tx.QueryRow(ctx, "SELECT status FROM till_sales WHERE id = $1", tillSaleID).Scan(&staleStatus); err != nil {
+		t.Fatalf("failed to query stale till sale: %v", err)
+	}
+	if err := tx.QueryRow(ctx, "SELECT status FROM till_sales WHERE id = $1", freshSaleID).Scan(&freshStatus); err != nil {
+		t.Fatalf("failed to query fresh till sale: %v", err)
+	}
+	if staleStatus != "failed" {
+		t.Errorf("expected stale pending till sale to be marked failed, got %q", staleStatus)
+	}
+	if freshStatus != "pending" {
+		t.Errorf("expected fresh pending till sale to stay pending, got %q", freshStatus)
+	}
+}
diff --git a/backend/handlers/payments/refunds.go b/backend/handlers/payments/refunds.go
index 9b61b6a..5203669 100644
--- a/backend/handlers/payments/refunds.go
+++ b/backend/handlers/payments/refunds.go
@@ -1052,13 +1052,26 @@ func processChargeGroup(ctx context.Context, chargeID string, rows []pendingChar
 	})
 	switch {
 	case sqErr == nil:
+		// Resolve by Square's status: COMPLETED resolves the group; PENDING
+		// leaves the rows pending (a later sweep reconciles them via
+		// ListPaymentRefunds); FAILED/REJECTED is a definitive failure that
+		// must not be marked completed (that would block the amount in the
+		// over-refund guard forever).
+		sqStatus := "completed"
+		if sqResult.Status == "PENDING" {
+			sqStatus = "pending"
+			log.Printf("Square refund %s for charge %s is PENDING — leaving refunds pending for the sweep", sqResult.ID, chargeID)
+		} else if sqResult.Status == "FAILED" || sqResult.Status == "REJECTED" {
+			sqStatus = "failed"
+			log.Printf("Square refund %s for charge %s FAILED — marking refunds failed", sqResult.ID, chargeID)
+		}
 		// ATOMIC — one statement for the whole group, never per-row. Keeps
 		// crash-retry amounts identical so Square's key-dedup returns the
 		// original refund.
 		if _, upErr := db.Conn.Exec(ctx, `
-			UPDATE refunds SET status = 'completed', square_refund_id = $1
-			WHERE id = ANY($2) AND status = 'pending'
-		`, sqResult.ID, idsOf(pending)); upErr != nil {
+			UPDATE refunds SET status = $1, square_refund_id = $2
+			WHERE id = ANY($3) AND status = 'pending'
+		`, sqStatus, sqResult.ID, idsOf(pending)); upErr != nil {
 			log.Printf("CRITICAL: Square refund committed (%s) but DB update for charge %s failed — manual reconciliation required: %v", sqResult.ID, chargeID, upErr)
 		}
 		return len(pending), nil
diff --git a/backend/handlers/payments/service.go b/backend/handlers/payments/service.go
index 5782b32..b3f1c8f 100644
--- a/backend/handlers/payments/service.go
+++ b/backend/handlers/payments/service.go
@@ -332,6 +332,12 @@ func (s *PaymentService) CheckIdempotencyByKey(ctx context.Context, idempotencyK
 
 func (s *PaymentService) GetPaymentByID(ctx context.Context, paymentID string) (*PaymentRecord, error) {
 	var p PaymentRecord
+	// booking_id / vendor_code / gift_card_id / invoice_number are nullable
+	// (e.g. gift-card purchases have no booking). Scan into Null* and map so a
+	// NULL value doesn't 500 the scan (N-3: the same fix class as
+	// CheckIdempotencyByKey).
+	var bookingID, vendorCode, giftCardID sql.NullString
+	var invoiceNumber sql.NullInt64
 	err := db.Conn.QueryRow(ctx, `
 		SELECT id, booking_id, payment_type, payment_method, vendor_code, invoice_number,
 		       status, amount, is_vat_applicable, vat_rate, vat_amount, net_amount,
@@ -340,15 +346,26 @@ func (s *PaymentService) GetPaymentByID(ctx context.Context, paymentID string) (
 		FROM payments
 		WHERE id = $1
 	`, paymentID).Scan(
-		&p.ID, &p.BookingID, &p.PaymentType, &p.PaymentMethod, &p.VendorCode, &p.InvoiceNumber,
+		&p.ID, &bookingID, &p.PaymentType, &p.PaymentMethod, &vendorCode, &invoiceNumber,
 		&p.Status, &p.Amount, &p.IsVATApplicable, &p.VATRate, &p.VATAmount, &p.NetAmount,
 		&p.UserSavedCardID, &p.SquarePaymentID, &p.IdempotencyKey, &p.Fees,
-		&p.CreatedAt, &p.UpdatedAt, &p.CreatedBy, &p.GiftCardID,
+		&p.CreatedAt, &p.UpdatedAt, &p.CreatedBy, &giftCardID,
 	)
 
 	if err != nil {
 		return nil, err
 	}
+	p.BookingID = bookingID.String
+	if vendorCode.Valid {
+		p.VendorCode = &vendorCode.String
+	}
+	if giftCardID.Valid {
+		p.GiftCardID = &giftCardID.String
+	}
+	if invoiceNumber.Valid {
+		n := int(invoiceNumber.Int64)
+		p.InvoiceNumber = &n
+	}
 	return &p, nil
 }
 
@@ -536,10 +553,22 @@ func (s *PaymentService) CreatePaymentMethodFromToken(ctx context.Context, userI
 
 	var savedCardID string
 	var isDefault bool
+	// ON CONFLICT (square_card_id): a response-lost retry re-tokenizes the same
+	// card (CreateCardOnFile's deterministic key returns the same ccof: id), so
+	// the UNIQUE constraint would otherwise 500 on the duplicate. Upsert instead
+	// so the retry returns the existing saved card (N-8).
 	err = db.Conn.QueryRow(ctx, `
 		INSERT INTO user_saved_cards (user_id, square_card_id, brand, last_4, exp_month, exp_year, fingerprint, is_default)
 		SELECT $1, $2, $3, $4, $5, $6, $7,
 			NOT EXISTS(SELECT 1 FROM user_saved_cards WHERE user_id = $1 AND deleted_at IS NULL)
+		ON CONFLICT (square_card_id) DO UPDATE SET
+			brand = EXCLUDED.brand,
+			last_4 = EXCLUDED.last_4,
+			exp_month = EXCLUDED.exp_month,
+			exp_year = EXCLUDED.exp_year,
+			fingerprint = EXCLUDED.fingerprint,
+			deleted_at = NULL,
+			retained_until = NULL
 		RETURNING id, is_default
 	`, userID, cardOnFile.CardID, cardOnFile.Brand, cardOnFile.Last4, cardOnFile.ExpMonth, cardOnFile.ExpYear, cardOnFile.Fingerprint).Scan(&savedCardID, &isDefault)
 	if err != nil {
diff --git a/backend/handlers/payments/sweep.go b/backend/handlers/payments/sweep.go
new file mode 100644
index 0000000..9835e69
--- /dev/null
+++ b/backend/handlers/payments/sweep.go
@@ -0,0 +1,74 @@
+package payments
+
+import (
+	"context"
+	"log"
+	"time"
+
+	"crussell/clock"
+	"crussell/db"
+)
+
+// SweepStalePendingPayments marks pending payment records that are older than
+// Square's idempotency-key retention window (~24h) as 'failed'. A pending
+// record means the DB committed but the Square charge outcome is unknown; it
+// normally resolves on a same-key client retry. But if the client abandoned
+// the attempt, the record stays pending forever — and retrying it after the
+// key expires would ISSUE A SECOND CHARGE (Square no longer dedups). Failing
+// stale pendings closes that double-charge window: a late retry finds a
+// 'failed' record and stops instead of charging again.
+//
+// Only online/till card payments can be pending — cash/giftcard/on_the_house
+// are committed synchronously and never enter this state. Both the payments
+// table and till_sales carry pending card-sale rows and are swept here.
+//
+// A swept row may have been genuinely charged at Square with a lost response —
+// it is flagged with a CRITICAL manual-reconciliation log (like the refund
+// sweep) so the money is not silently lost in limbo (MINOR-R3).
+const stalePendingPaymentAge = 24 * time.Hour
+
+func SweepStalePendingPayments(ctx context.Context) (int, error) {
+	cutoff := clock.Now().Add(-stalePendingPaymentAge)
+
+	tag, err := db.Conn.Exec(ctx, `
+		UPDATE payments
+		SET status = 'failed', updated_at = NOW()
+		WHERE status = 'pending'
+		  AND created_at < $1
+	`, cutoff)
+	if err != nil {
+		return 0, err
+	}
+	payCount := int(tag.RowsAffected())
+
+	// till_sales rows for card payments (stored as 'online_square' or
+	// 'in_person_card' in the payment_method enum — saved_card/online_square/
+	// card_machine requests all persist as one of those) can also be pending.
+	// Sweep them too — a lost-response till sale would otherwise stay pending
+	// and a retry after key retention would reuse the stored key → Square sees
+	// an expired key → second charge (R3). Cash / on_the_house are committed
+	// synchronously and never pending.
+	tillTag, err := db.Conn.Exec(ctx, `
+		UPDATE till_sales
+		SET status = 'failed', updated_at = NOW()
+		WHERE status = 'pending'
+		  AND created_at < $1
+		  AND payment_method IN ('online_square', 'in_person_card')
+	`, cutoff)
+	if err != nil {
+		return 0, err
+	}
+	tillCount := int(tillTag.RowsAffected())
+
+	total := payCount + tillCount
+	if total > 0 {
+		log.Printf("[SWEEP] Marked %d stale pending payments (%d payments, %d till sales) as failed (older than %s) — late retries will be rejected, preventing a second Square charge", total, payCount, tillCount, stalePendingPaymentAge)
+	}
+	if payCount > 0 {
+		log.Printf("CRITICAL: %d pending payments swept to failed may have been charged at Square with a lost response — manual reconciliation required before refunding/charging", payCount)
+	}
+	if tillCount > 0 {
+		log.Printf("CRITICAL: %d pending till sales swept to failed may have been charged at Square with a lost response — manual reconciliation required", tillCount)
+	}
+	return total, nil
+}
diff --git a/backend/handlers/payments/till.go b/backend/handlers/payments/till.go
index 4e42ae1..45cd25f 100644
--- a/backend/handlers/payments/till.go
+++ b/backend/handlers/payments/till.go
@@ -56,6 +56,12 @@ func uniqueTillKey() string {
 
 func CreateTillSale(w http.ResponseWriter, r *http.Request) {
 	ctx := r.Context()
+	// Defense-in-depth admin check (S-1) — a till sale moves money (charges a
+	// card / funds a gift card), so it must stay admin-only.
+	if !isAdminRequest(r) {
+		http.Error(w, "Admin access required", http.StatusForbidden)
+		return
+	}
 	adminID, _ := ctx.Value(mw.UserIDKey).(string)
 
 	var req TillSaleRequest
@@ -70,9 +76,6 @@ func CreateTillSale(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	// M8
-	// L5
-
 	if req.ItemType != "gift_card" {
 		http.Error(w, "Unsupported item type", http.StatusBadRequest)
 		return
@@ -180,6 +183,13 @@ func CreateTillSale(w http.ResponseWriter, r *http.Request) {
 				existingPendingID = existingID
 				existingPendingGiftCard = existingItemID
 			}
+			if existingStatus == "failed" {
+				// Swept as stale (>24h) or definitively rejected — a retry would
+				// risk a second Square charge. Reject cleanly (R2).
+				log.Printf("Till-sale retry rejected: record %s was marked failed", existingID)
+				http.Error(w, "This till sale previously failed and can no longer be retried", http.StatusConflict)
+				return
+			}
 		}
 	}
 
@@ -558,6 +568,11 @@ func CreateTillSale(w http.ResponseWriter, r *http.Request) {
 				http.Error(w, "card_token is required for online_square payment — use a Square Web Payments nonce", http.StatusBadRequest)
 				return
 			}
+			// Tokenize the till card. The reference_id is the synthetic
+			// "till-<giftCardID>" namespace, NOT a real user — this card is
+			// ephemeral (used once for this charge) and is never stored in
+			// user_saved_cards or re-listed. The prefix can't collide with a
+			// real CHAR(12)-hex user ID.
 			cardOnFile, cardErr := SquareClient.CreateCardOnFile(ctx, "till-"+giftCardID, req.CardToken)
 			if cardErr != nil {
 				log.Printf("Failed to tokenize card: %v", cardErr)
@@ -630,6 +645,11 @@ func CreateTillSale(w http.ResponseWriter, r *http.Request) {
 }
 
 func GetTillCheckoutStatus(w http.ResponseWriter, r *http.Request) {
+	// Defense-in-depth admin check (S-1).
+	if !isAdminRequest(r) {
+		http.Error(w, "Admin access required", http.StatusForbidden)
+		return
+	}
 	checkoutID := chi.URLParam(r, "checkout_id")
 	if checkoutID == "" {
 		http.Error(w, "Checkout ID is required", http.StatusBadRequest)
@@ -675,6 +695,33 @@ func GetTillCheckoutStatus(w http.ResponseWriter, r *http.Request) {
 	}
 
 	if paymentResult.Status == "COMPLETED" {
+		// Serialize terminal-completion records per till sale — the one payment
+		// writer that previously lacked the advisory-lock pattern every other
+		// path uses. Two concurrent polls of the same checkout could both run
+		// the UPDATE + VAT (idempotent today, but a double-apply is a latent
+		// bug). Lock on the till-sale id so only one goroutine completes it.
+		pinConn, err := db.Conn.Acquire(r.Context())
+		if err != nil {
+			log.Printf("Failed to acquire connection for till-completion lock: %v", err)
+			http.Error(w, "internal server error", http.StatusInternalServerError)
+			return
+		}
+		defer pinConn.Release()
+		if _, err := pinConn.Exec(r.Context(), `
+			SELECT pg_advisory_lock(hashtext('crussell:tillcomplete:' || $1))
+		`, tillSaleID); err != nil {
+			log.Printf("Failed to acquire till-completion serialization lock for %s: %v", tillSaleID, err)
+			http.Error(w, "internal server error", http.StatusInternalServerError)
+			return
+		}
+		defer func() {
+			if _, err := pinConn.Exec(context.Background(), `
+				SELECT pg_advisory_unlock(hashtext('crussell:tillcomplete:' || $1))
+			`, tillSaleID); err != nil {
+				log.Printf("Failed to release till-completion serialization lock for %s: %v", tillSaleID, err)
+			}
+		}()
+
 		tx, err := db.Conn.Begin(r.Context())
 		if err != nil {
 			log.Printf("Failed to begin transaction: %v", err)
diff --git a/backend/handlers/payments/till_test.go b/backend/handlers/payments/till_test.go
index 5edfbaf..e9042d5 100644
--- a/backend/handlers/payments/till_test.go
+++ b/backend/handlers/payments/till_test.go
@@ -416,6 +416,7 @@ func TestGetTillCheckoutStatus_NotFound(t *testing.T) {
 	rctx.URLParams.Add("checkout_id", "nonexistent")
 	reqCtx := context.WithValue(req.Context(), chi.RouteCtxKey, rctx)
 	req = req.WithContext(reqCtx)
+	req = adminRequestCtx(req)
 
 	w := httptest.NewRecorder()
 	GetTillCheckoutStatus(w, req)
@@ -482,6 +483,8 @@ func TestGetTillCheckoutStatus_Pending(t *testing.T) {
 	statusReqCtx = db.ContextWithTx(statusReqCtx, tx.(pgx.Tx))
 	statusReq = statusReq.WithContext(statusReqCtx)
 
+	statusReq = adminRequestCtx(statusReq)
+
 	wStatus := httptest.NewRecorder()
 	GetTillCheckoutStatus(wStatus, statusReq)
 
@@ -555,6 +558,8 @@ func TestGetTillCheckoutStatus_Completed(t *testing.T) {
 	statusReqCtx = db.ContextWithTx(statusReqCtx, tx.(pgx.Tx))
 	statusReq = statusReq.WithContext(statusReqCtx)
 
+	statusReq = adminRequestCtx(statusReq)
+
 	wStatus := httptest.NewRecorder()
 	GetTillCheckoutStatus(wStatus, statusReq)
 
@@ -624,6 +629,8 @@ func TestGetTillCheckoutStatus_AlreadyCompleted(t *testing.T) {
 	statusReqCtx := context.WithValue(statusReq.Context(), chi.RouteCtxKey, statusRCtx)
 	statusReq = statusReq.WithContext(statusReqCtx)
 
+	statusReq = adminRequestCtx(statusReq)
+
 	wStatus := httptest.NewRecorder()
 	GetTillCheckoutStatus(wStatus, statusReq)
 
@@ -640,9 +647,11 @@ func TestGetTillCheckoutStatus_EmptyCheckoutID(t *testing.T) {
 	rctx.URLParams.Add("checkout_id", "")
 	reqCtx := context.WithValue(req.Context(), chi.RouteCtxKey, rctx)
 	req = req.WithContext(reqCtx)
+	req = adminRequestCtx(req)
 
 	w := httptest.NewRecorder()
 	GetTillCheckoutStatus(w, req)
+	req = adminRequestCtx(req)
 
 	if w.Code != http.StatusBadRequest {
 		t.Errorf("expected status 400, got %d. body: %s", w.Code, w.Body.String())
diff --git a/backend/handlers/webhooks/square.go b/backend/handlers/webhooks/square.go
index 91067f7..10bd03d 100644
--- a/backend/handlers/webhooks/square.go
+++ b/backend/handlers/webhooks/square.go
@@ -34,23 +34,30 @@ func HandleSquareWebhook(w http.ResponseWriter, r *http.Request) {
 	// in env vars (see Square Developer Console → Webhooks → Subscription).
 	// Reference: https://developer.squareup.com/docs/webhooks/step3validate
 
+	// Fail closed: a missing signing key means the webhook cannot be verified,
+	// so reject rather than process unauthenticated events (S-4). Square
+	// always sends the signature header, so an unset key in production is a
+	// misconfiguration that must not silently accept forged events.
 	signingKey := os.Getenv("SQUARE_WEBHOOK_SIGNATURE_KEY")
 	notificationURL := os.Getenv("SQUARE_WEBHOOK_NOTIFICATION_URL")
 	if notificationURL == "" {
 		notificationURL = "http://localhost:8080/webhooks/square"
 	}
-	if signingKey != "" {
-		signature := r.Header.Get("x-square-hmacsha256-signature")
-		if signature == "" {
-			log.Printf("Missing Square webhook signature header")
-			http.Error(w, "Invalid signature", http.StatusForbidden)
-			return
-		}
-		if !verifySquareSignature(body, signature, signingKey, notificationURL) {
-			log.Printf("Invalid Square webhook signature")
-			http.Error(w, "Invalid signature", http.StatusForbidden)
-			return
-		}
+	if signingKey == "" {
+		log.Printf("SQUARE_WEBHOOK_SIGNATURE_KEY is not set — rejecting webhook (fail-closed)")
+		http.Error(w, "webhook signature verification unavailable", http.StatusServiceUnavailable)
+		return
+	}
+	signature := r.Header.Get("x-square-hmacsha256-signature")
+	if signature == "" {
+		log.Printf("Missing Square webhook signature header")
+		http.Error(w, "Invalid signature", http.StatusForbidden)
+		return
+	}
+	if !verifySquareSignature(body, signature, signingKey, notificationURL) {
+		log.Printf("Invalid Square webhook signature")
+		http.Error(w, "Invalid signature", http.StatusForbidden)
+		return
 	}
 
 	var event SquareWebhookEvent
diff --git a/backend/handlers/webhooks/webhooks_test.go b/backend/handlers/webhooks/webhooks_test.go
index 552cb97..9715395 100644
--- a/backend/handlers/webhooks/webhooks_test.go
+++ b/backend/handlers/webhooks/webhooks_test.go
@@ -111,8 +111,20 @@ func makeWebhookRequest(body []byte, signature string, ctx context.Context) *htt
 	return w
 }
 
+// webhookTestEnv sets a signing key and returns a valid signature for the body
+// (the fail-closed handler requires a verifiable signature on every request).
+func webhookTestEnv(t *testing.T, body []byte) (signature string) {
+	t.Helper()
+	tKey := "test-signing-key"
+	tURL := "http://localhost:8080/webhooks/square"
+	mac := hmac.New(sha256.New, []byte(tKey))
+	mac.Write([]byte(tURL))
+	mac.Write(body)
+	t.Setenv("SQUARE_WEBHOOK_SIGNATURE_KEY", tKey)
+	return base64.StdEncoding.EncodeToString(mac.Sum(nil))
+}
+
 func TestHandleSquareWebhook_PaymentUpdated(t *testing.T) {
-	t.Parallel()
 	event := SquareWebhookEvent{
 		Type:      "payment.updated",
 		EventID:   "evt_payment_1",
@@ -120,7 +132,8 @@ func TestHandleSquareWebhook_PaymentUpdated(t *testing.T) {
 		Data:      json.RawMessage(`{"id":"payment_1"}`),
 	}
 	body, _ := json.Marshal(event)
-	w := makeWebhookRequest(body, "", context.Background())
+	sig := webhookTestEnv(t, body)
+	w := makeWebhookRequest(body, sig, context.Background())
 	if w.Code != http.StatusOK {
 		t.Errorf("expected 200, got %d. body: %s", w.Code, w.Body.String())
 	}
@@ -130,7 +143,6 @@ func TestHandleSquareWebhook_PaymentUpdated(t *testing.T) {
 }
 
 func TestHandleSquareWebhook_RefundUpdated(t *testing.T) {
-	t.Parallel()
 	event := SquareWebhookEvent{
 		Type:      "refund.updated",
 		EventID:   "evt_refund_1",
@@ -138,14 +150,14 @@ func TestHandleSquareWebhook_RefundUpdated(t *testing.T) {
 		Data:      json.RawMessage(`{"id":"refund_1"}`),
 	}
 	body, _ := json.Marshal(event)
-	w := makeWebhookRequest(body, "", context.Background())
+	sig := webhookTestEnv(t, body)
+	w := makeWebhookRequest(body, sig, context.Background())
 	if w.Code != http.StatusOK {
 		t.Errorf("expected 200, got %d. body: %s", w.Code, w.Body.String())
 	}
 }
 
 func TestHandleSquareWebhook_DisputeCreated(t *testing.T) {
-	t.Parallel()
 	event := SquareWebhookEvent{
 		Type:      "dispute.created",
 		EventID:   "evt_dispute_1",
@@ -153,14 +165,14 @@ func TestHandleSquareWebhook_DisputeCreated(t *testing.T) {
 		Data:      json.RawMessage(`{"id":"dispute_1"}`),
 	}
 	body, _ := json.Marshal(event)
-	w := makeWebhookRequest(body, "", context.Background())
+	sig := webhookTestEnv(t, body)
+	w := makeWebhookRequest(body, sig, context.Background())
 	if w.Code != http.StatusOK {
 		t.Errorf("expected 200 for dispute.created, got %d. body: %s", w.Code, w.Body.String())
 	}
 }
 
 func TestHandleSquareWebhook_UnknownEventType(t *testing.T) {
-	t.Parallel()
 	event := SquareWebhookEvent{
 		Type:      "invoice.created",
 		EventID:   "evt_unknown_1",
@@ -168,25 +180,27 @@ func TestHandleSquareWebhook_UnknownEventType(t *testing.T) {
 		Data:      json.RawMessage(`{"id":"inv_1"}`),
 	}
 	body, _ := json.Marshal(event)
-	w := makeWebhookRequest(body, "", context.Background())
+	sig := webhookTestEnv(t, body)
+	w := makeWebhookRequest(body, sig, context.Background())
 	if w.Code != http.StatusOK {
 		t.Errorf("expected 200 for unknown event type, got %d. body: %s", w.Code, w.Body.String())
 	}
 }
 
 func TestHandleSquareWebhook_InvalidJSON(t *testing.T) {
-	t.Parallel()
-	w := makeWebhookRequest([]byte(`{invalid json}`), "", context.Background())
+	body := []byte(`{invalid json}`)
+	sig := webhookTestEnv(t, body)
+	w := makeWebhookRequest(body, sig, context.Background())
 	if w.Code != http.StatusBadRequest {
 		t.Errorf("expected 400 for invalid JSON, got %d. body: %s", w.Code, w.Body.String())
 	}
 }
 
 func TestHandleSquareWebhook_BodyTooLarge(t *testing.T) {
-	t.Parallel()
 	// 600KB body exceeds the 512KB limit
 	largeBody := []byte(strings.Repeat("a", 600*1024))
-	w := makeWebhookRequest(largeBody, "", context.Background())
+	sig := webhookTestEnv(t, largeBody)
+	w := makeWebhookRequest(largeBody, sig, context.Background())
 	if w.Code != http.StatusRequestEntityTooLarge {
 		t.Errorf("expected 413 for oversized body, got %d. body: %s", w.Code, w.Body.String())
 	}
@@ -236,14 +250,15 @@ func TestHandleSquareWebhook_NoSignatureWhenKeySet(t *testing.T) {
 	}
 }
 
-func TestHandleSquareWebhook_SignatureSkippedWhenKeyEmpty(t *testing.T) {
+func TestHandleSquareWebhook_RejectedWhenKeyEmpty(t *testing.T) {
 
 	t.Setenv("SQUARE_WEBHOOK_SIGNATURE_KEY", "")
 
 	body := []byte(`{"type":"payment.updated","event_id":"evt_1"}`)
-	// Bad signature but key is empty, so verification should be skipped
+	// Fail-closed: an unset signing key means the webhook cannot be verified,
+	// so the request is rejected rather than accepted with a bad signature.
 	w := makeWebhookRequest(body, "some-signature", context.Background())
-	if w.Code != http.StatusOK {
-		t.Errorf("expected 200 when no key configured (dev stub), got %d. body: %s", w.Code, w.Body.String())
+	if w.Code != http.StatusServiceUnavailable {
+		t.Errorf("expected 503 when no key configured (fail-closed), got %d. body: %s", w.Code, w.Body.String())
 	}
 }
diff --git a/backend/internal/jobs/cleanup.go b/backend/internal/jobs/cleanup.go
index b8115ea..b9fe852 100644
--- a/backend/internal/jobs/cleanup.go
+++ b/backend/internal/jobs/cleanup.go
@@ -56,6 +56,16 @@ func RegisterAll(s *Scheduler) {
 		Handler:     payments.SweepPendingSquareRefunds,
 	})
 
+	// Offset from the refund sweep (which also writes payments rows) by one
+	// minute to avoid the two sweeps contending on the same table.
+	s.Register(Job{
+		Name:        "sweep-stale-pending-payments",
+		Schedule:    "1,6,11,16,21,26,31,36,41,46,51,56 * * * *",
+		Timeout:     60 * time.Second,
+		Concurrency: 1,
+		Handler:     payments.SweepStalePendingPayments,
+	})
+
 	// === MID FREQUENCY — every minute (progressive rate limiter was on 30s) ===
 
 	s.Register(Job{
diff --git a/backend/internal/jobs/scheduler_test.go b/backend/internal/jobs/scheduler_test.go
index 41ed830..3e705ee 100644
--- a/backend/internal/jobs/scheduler_test.go
+++ b/backend/internal/jobs/scheduler_test.go
@@ -413,8 +413,8 @@ func TestRegisterAll_RegistersExpectedJobs(t *testing.T) {
 	s := New()
 	RegisterAll(s)
 
-	if got := len(s.registry); got != 21 {
-		t.Fatalf("RegisterAll() registered %d jobs, want 21", got)
+	if got := len(s.registry); got != 22 {
+		t.Fatalf("RegisterAll() registered %d jobs, want 22", got)
 	}
 
 	registered := make(map[string]Job, len(s.registry))
@@ -473,6 +473,7 @@ func expectedJobNames() map[string]bool {
 		"cleanup-rate-limiters":               true,
 		"cleanup-gdpr-export-cache":           true,
 		"sweep-pending-square-refunds":        true,
+		"sweep-stale-pending-payments":        true,
 		"cleanup-progressive-rate-limiter":    true,
 		"cleanup-expired-loyalty-redemptions": true,
 		"cleanup-old-idempotency-keys":        true,
diff --git a/backend/internal/square/square_dev.go b/backend/internal/square/square_dev.go
index f236a6f..cfb47ce 100644
--- a/backend/internal/square/square_dev.go
+++ b/backend/internal/square/square_dev.go
@@ -108,7 +108,16 @@ func (m *MockClient) CreatePayment(ctx context.Context, req CreatePaymentReq) (*
 	if m.ShouldFail {
 		return nil, fmt.Errorf("mock: payment declined (simulated failure)")
 	}
-	log.Printf("[SQUARE-MOCK] CreatePayment: amount=%d, reference=%s, source=%s", req.Amount, req.ReferenceID, req.SourceID)
+	// Do NOT log the full source token — it is a single-use nonce (cnon:) or a
+	// card reference (ccof:) that could be replayed. Log only its prefix and
+	// length for debugging (S-2).
+	sourcePrefix := ""
+	if len(req.SourceID) > 8 {
+		sourcePrefix = req.SourceID[:8] + "..."
+	} else {
+		sourcePrefix = req.SourceID
+	}
+	log.Printf("[SQUARE-MOCK] CreatePayment: amount=%d, reference=%s, source=%s", req.Amount, req.ReferenceID, sourcePrefix)
 	mockSleep(1 * time.Second)
 
 	m.mu.Lock()
@@ -199,7 +208,6 @@ func (m *MockClient) CreateCheckout(ctx context.Context, req CreateCheckoutReq)
 		Status:      "PENDING",
 		AmountMoney: req.Amount,
 		Currency:    req.Currency,
-		DeviceID:    req.DeviceID,
 		ReferenceID: req.ReferenceID,
 		Note:        req.Note,
 		CreatedAt:   now.Format(time.RFC3339),
@@ -383,7 +391,11 @@ func (m *MockClient) CreateCardOnFile(ctx context.Context, userID, cardToken str
 	brand, last4 := detectCardInfo(cardToken)
 	card := &CardOnFile{
 		ID:             cardID,
-		CardID:         fmt.Sprintf("ccof_mock_%d", now.UnixNano()),
+		// Prefix "ccof:" so the mock's own entry-method detection (and any
+		// consumer checking the prefix) sees ON_FILE, matching production where
+		// saved-card tokens are "ccof:xxx". An "ccof_mock_" id would silently
+		// exercise the KEYED path in tests while prod runs ON_FILE.
+		CardID:         fmt.Sprintf("ccof:mock_%d", now.UnixNano()),
 		Brand:          brand,
 		Last4:          last4,
 		ExpMonth:       12,
diff --git a/backend/internal/square/square_http_client.go b/backend/internal/square/square_http_client.go
index 801e235..2582860 100644
--- a/backend/internal/square/square_http_client.go
+++ b/backend/internal/square/square_http_client.go
@@ -39,6 +39,7 @@ type httpClient struct {
 	baseURL    string
 	token      string
 	locationID string
+	deviceID   string
 	http       *http.Client
 }
 
@@ -52,6 +53,7 @@ func newHTTPClient() *httpClient {
 		baseURL:    baseURL,
 		token:      os.Getenv("SQUARE_ACCESS_TOKEN"),
 		locationID: os.Getenv("SQUARE_LOCATION_ID"),
+		deviceID:   os.Getenv("SQUARE_TERMINAL_DEVICE_ID"),
 		http:       &http.Client{Timeout: defaultHTTPTimeout},
 	}
 }
@@ -174,9 +176,12 @@ type sqCard struct {
 	CreatedAt      string `json:"created_at"`
 }
 
+// sqFee matches Square's processing_fee object. The fee amount lives in
+// amount_money.amount, NOT a top-level amount field — reading the wrong shape
+// made every PaymentResult.Fees 0 against the real API (N-9).
 type sqFee struct {
-	Amount int64  `json:"amount"`
-	Type   string `json:"type"`
+	AmountMoney sqMoney `json:"amount_money"`
+	Type        string  `json:"type"`
 }
 
 // --- Terminal Checkout types ---
@@ -206,7 +211,6 @@ type sqTerminalCheckout struct {
 	ID          string   `json:"id"`
 	Status      string   `json:"status"`
 	AmountMoney sqMoney  `json:"amount_money"`
-	DeviceID    string   `json:"device_id,omitempty"`
 	ReferenceID string   `json:"reference_id,omitempty"`
 	Note        string   `json:"note,omitempty"`
 	PaymentIDs  []string `json:"payment_ids,omitempty"`
@@ -268,7 +272,8 @@ type sqCreateCardResponse struct {
 }
 
 type sqListCardsResponse struct {
-	Cards []sqCard `json:"cards"`
+	Cards  []sqCard `json:"cards"`
+	Cursor string   `json:"cursor"`
 }
 
 type sqDisableCardResponse struct {
@@ -312,6 +317,13 @@ func createCheckoutHTTP(ctx context.Context, req CreateCheckoutReq) (*CheckoutRe
 }
 
 func createCheckoutHTTPWithClient(ctx context.Context, req CreateCheckoutReq, hc *httpClient) (*CheckoutResult, error) {
+	// device_options is REQUIRED by Square's TerminalCheckout API. Prefer the
+	// per-request device ID, falling back to the env-configured terminal
+	// (SQUARE_TERMINAL_DEVICE_ID) so the field is always present.
+	deviceID := req.DeviceID
+	if deviceID == "" {
+		deviceID = hc.deviceID
+	}
 	body := sqTerminalCheckoutRequest{
 		IdempotencyKey: req.IdempotencyKey,
 		Checkout: sqTerminalCheckoutPayload{
@@ -319,11 +331,11 @@ func createCheckoutHTTPWithClient(ctx context.Context, req CreateCheckoutReq, hc
 			ReferenceID: req.ReferenceID,
 			Note:        req.Note,
 			CustomerID:  req.CustomerID,
+			DeviceOptions: &sqDeviceOptions{
+				DeviceID: deviceID,
+			},
 		},
 	}
-	if req.DeviceID != "" {
-		body.Checkout.DeviceOptions = &sqDeviceOptions{DeviceID: req.DeviceID}
-	}
 	var resp sqTerminalCheckoutResponse
 	if err := hc.doJSON(ctx, http.MethodPost, "/v2/terminals/checkouts", body, &resp); err != nil {
 		return nil, err
@@ -342,7 +354,11 @@ func getCheckoutHTTPWithClient(ctx context.Context, checkoutID string, hc *httpC
 	}
 	tc := tcResp.Checkout
 	if tc.Status != "COMPLETED" {
-		if tc.Status == "PENDING" || tc.Status == "IN_PROGRESS" {
+		// PENDING / IN_PROGRESS / CANCEL_REQUESTED all mean the terminal
+		// hasn't finished — treat as still-polling. Anything else (e.g.
+		// CANCELED) is terminal but not a completed payment.
+		switch tc.Status {
+		case "PENDING", "IN_PROGRESS", "CANCEL_REQUESTED":
 			return nil, ErrCheckoutPending
 		}
 		return nil, fmt.Errorf("square: checkout %s is %s (not COMPLETED)", checkoutID, tc.Status)
@@ -372,13 +388,15 @@ func (e *squareAPIError) Unwrap() error { return e.err }
 // Definitive Square refund rejection codes — the refund was declined and can
 // never succeed, so retrying is pointless and the refund record should be
 // marked 'failed'. Anything else (transport errors, 5xx) is left ambiguous so
-// callers leave the refund 'pending' for a scheduler retry. Note that
-// PAYMENT_ALREADY_REFUNDED is intentionally absent — the money has already
-// moved, so it maps to ErrRefundAlreadyProcessed instead of ErrRefundDeclined.
+// callers leave the refund 'pending' for a scheduler retry. Codes match
+// Square's documented Refunds error list (REFUND_DECLINED, REFUND_AMOUNT_INVALID,
+// PAYMENT_NOT_REFUNDABLE); note PAYMENT_ALREADY_REFUNDED and
+// REFUND_ALREADY_PENDING are intentionally absent — money is in flight or has
+// moved, so they map to ErrRefundAlreadyProcessed instead of ErrRefundDeclined.
 var definitiveRefundCodes = map[string]bool{
-	"REFUND_DECLINED":                true,
-	"PAYMENT_REFUND_AMOUNT_EXCEEDED": true,
-	"INVALID_PAYMENT_ID":             true,
+	"REFUND_DECLINED":       true,
+	"REFUND_AMOUNT_INVALID": true,
+	"PAYMENT_NOT_REFUNDABLE": true,
 }
 
 func refundPaymentHTTP(ctx context.Context, req RefundPaymentReq) (*RefundResult, error) {
@@ -398,7 +416,7 @@ func refundPaymentHTTPWithClient(ctx context.Context, req RefundPaymentReq, hc *
 		if errors.As(err, &sqErr) && definitiveRefundCodes[sqErr.Code] {
 			return nil, fmt.Errorf("%w: %v", ErrRefundDeclined, err)
 		}
-		if errors.As(err, &sqErr) && sqErr.Code == "PAYMENT_ALREADY_REFUNDED" {
+		if errors.As(err, &sqErr) && (sqErr.Code == "PAYMENT_ALREADY_REFUNDED" || sqErr.Code == "REFUND_ALREADY_PENDING") {
 			return nil, fmt.Errorf("%w: %v", ErrRefundAlreadyProcessed, err)
 		}
 		return nil, err
@@ -442,9 +460,11 @@ func createCardOnFileHTTPWithClient(ctx context.Context, userID, cardToken strin
 	// Deterministic idempotency key derived from user + card (not time-based)
 	// so that retries with the same details don't create duplicate cards.
 	// SHA-256 hash prevents recovering the card token from the key itself.
+	// Truncated to ≤45 chars — Square's documented idempotency-key limit for
+	// /v2/cards (a full 64-hex hash would be rejected with a 400).
 	ikHash := sha256.Sum256([]byte(userID + "|" + cardToken))
 	body := sqCreateCardRequest{
-		IdempotencyKey: fmt.Sprintf("create-card-%x", ikHash),
+		IdempotencyKey: "card-" + fmt.Sprintf("%x", ikHash)[:38],
 		SourceID:       cardToken,
 		Card: sqCardPayload{
 			// The app does not provision Square customers, so the local user
@@ -469,15 +489,25 @@ func getCardsOnFileHTTPWithClient(ctx context.Context, userID string, hc *httpCl
 	// Filter by reference_id natively: Square's List Cards API supports the
 	// reference_id query param, and cards are created with reference_id = the
 	// local user ID (the app has no Square customers, so customer_id cannot be
-	// used). This avoids both the invalid customer_id filter and a client-side
-	// filter across a cursor-paginated list.
-	var resp sqListCardsResponse
-	if err := hc.doJSON(ctx, http.MethodGet, "/v2/cards?reference_id="+url.QueryEscape(userID), nil, &resp); err != nil {
-		return nil, err
+	// used). List Cards pages at 25 cards, so loop on the cursor to avoid
+	// silently truncating a large saved-card list (N-10).
+	var cards []CardOnFile
+	path := "/v2/cards?reference_id=" + url.QueryEscape(userID)
+	for page := 0; page < 20; page++ {
+		var resp sqListCardsResponse
+		if err := hc.doJSON(ctx, http.MethodGet, path, nil, &resp); err != nil {
+			return nil, err
+		}
+		for i := range resp.Cards {
+			cards = append(cards, *cardFromSquare(&resp.Cards[i], userID))
+		}
+		if resp.Cursor == "" {
+			break
+		}
+		path = "/v2/cards?reference_id=" + url.QueryEscape(userID) + "&cursor=" + url.QueryEscape(resp.Cursor)
 	}
-	cards := make([]CardOnFile, 0, len(resp.Cards))
-	for i := range resp.Cards {
-		cards = append(cards, *cardFromSquare(&resp.Cards[i], userID))
+	if cards == nil {
+		cards = []CardOnFile{}
 	}
 	return cards, nil
 }
@@ -515,7 +545,7 @@ func paymentFromSquare(sq *sqPayment) *PaymentResult {
 		r.TipAmount = sq.TipMoney.Amount
 	}
 	for _, f := range sq.ProcessingFee {
-		r.Fees += f.Amount
+		r.Fees += f.AmountMoney.Amount
 	}
 	if sq.CardDetails != nil {
 		cd := sq.CardDetails
@@ -543,7 +573,6 @@ func checkoutFromSquare(sq *sqTerminalCheckout) *CheckoutResult {
 		Status:      sq.Status,
 		AmountMoney: sq.AmountMoney.Amount,
 		Currency:    sq.AmountMoney.Currency,
-		DeviceID:    sq.DeviceID,
 		ReferenceID: sq.ReferenceID,
 		Note:        sq.Note,
 		PaymentIDs:  sq.PaymentIDs,
diff --git a/backend/internal/square/square_http_client_test.go b/backend/internal/square/square_http_client_test.go
index 5402d45..02c96c2 100644
--- a/backend/internal/square/square_http_client_test.go
+++ b/backend/internal/square/square_http_client_test.go
@@ -284,7 +284,9 @@ func TestCreatePaymentHTTP_TipMoneyAbsentWhenNil(t *testing.T) {
 }
 
 // TestRefundPaymentHTTP_CodeClassification verifies definitive refund rejection
-// codes map to ErrRefundDeclined, PAYMENT_ALREADY_REFUNDED maps to
+// codes (Square's documented list: REFUND_DECLINED, REFUND_AMOUNT_INVALID,
+// PAYMENT_NOT_REFUNDABLE) map to ErrRefundDeclined, the money-in-flight codes
+// (PAYMENT_ALREADY_REFUNDED, REFUND_ALREADY_PENDING) map to
 // ErrRefundAlreadyProcessed, and ambiguous errors pass through unwrapped.
 func TestRefundPaymentHTTP_CodeClassification(t *testing.T) {
 	cases := []struct {
@@ -294,9 +296,10 @@ func TestRefundPaymentHTTP_CodeClassification(t *testing.T) {
 		wantErrNil bool
 	}{
 		{name: "refund_declined", code: "REFUND_DECLINED", wantErrIs: ErrRefundDeclined},
-		{name: "amount_exceeded", code: "PAYMENT_REFUND_AMOUNT_EXCEEDED", wantErrIs: ErrRefundDeclined},
-		{name: "invalid_payment_id", code: "INVALID_PAYMENT_ID", wantErrIs: ErrRefundDeclined},
+		{name: "amount_invalid", code: "REFUND_AMOUNT_INVALID", wantErrIs: ErrRefundDeclined},
+		{name: "payment_not_refundable", code: "PAYMENT_NOT_REFUNDABLE", wantErrIs: ErrRefundDeclined},
 		{name: "already_refunded", code: "PAYMENT_ALREADY_REFUNDED", wantErrIs: ErrRefundAlreadyProcessed},
+		{name: "already_pending", code: "REFUND_ALREADY_PENDING", wantErrIs: ErrRefundAlreadyProcessed},
 		{name: "ambiguous_code", code: "INTERNAL_SERVER_ERROR", wantErrIs: nil},
 		{name: "ambiguous_non_json", code: "", wantErrIs: nil}, // raw text body
 	}
@@ -551,10 +554,15 @@ func TestCreateCardOnFileHTTP_IdempotencyKey(t *testing.T) {
 	}
 
 	sum := sha256.Sum256([]byte("user_1|cnon:test-card"))
-	wantIK := fmt.Sprintf("create-card-%x", sum)
+	wantIK := "card-" + fmt.Sprintf("%x", sum)[:38]
 	if captured["idempotency_key"] != wantIK {
 		t.Errorf("expected idempotency_key %q, got %v", wantIK, captured["idempotency_key"])
 	}
+	// Square's documented idempotency-key limit for /v2/cards is 45 chars —
+	// the truncated key must never exceed it (C-1 regression guard).
+	if len(wantIK) > 45 {
+		t.Errorf("idempotency_key %q is %d chars, exceeds Square's 45-char limit", wantIK, len(wantIK))
+	}
 	if captured["source_id"] != "cnon:test-card" {
 		t.Errorf("expected source_id cnon:test-card, got %v", captured["source_id"])
 	}
diff --git a/backend/internal/square/types.go b/backend/internal/square/types.go
index c3d9963..d0c41f8 100644
--- a/backend/internal/square/types.go
+++ b/backend/internal/square/types.go
@@ -100,7 +100,6 @@ type CheckoutResult struct {
 	Status      string   // "PENDING", "IN_PROGRESS", "COMPLETED", "CANCELED", "FAILED"
 	AmountMoney int64    // checkout amount in pence
 	Currency    string   // "GBP"
-	DeviceID    string   // terminal device ID
 	ReferenceID string   // client reference
 	Note        string   // optional note
 	PaymentIDs  []string // payment ID(s) once completed
diff --git a/backend/internal/validators/validators.go b/backend/internal/validators/validators.go
index 5dee1e0..ae4ff80 100644
--- a/backend/internal/validators/validators.go
+++ b/backend/internal/validators/validators.go
@@ -35,6 +35,19 @@ func IsValidID(id string) bool {
 	return validIDRegex.MatchString(id)
 }
 
+// Square checkout IDs are opaque strings (e.g. "08YceKh7B3ZqO") — NOT local
+// 12-hex DB IDs, so IsValidID must not gate them (it would 404 every real
+// checkout). Accept any non-empty ID matching Square's character set with a
+// sane length bound, and reject anything that could inject into the URL path.
+var squareCheckoutIDRegex = regexp.MustCompile(`^[A-Za-z0-9_\-]{8,64}$`)
+
+func IsValidSquareCheckoutID(id string) bool {
+	if id == "" {
+		return false
+	}
+	return squareCheckoutIDRegex.MatchString(id)
+}
+
 // ParseCursor splits a "createdAt|id" cursor string into its components.
 func ParseCursor(cursor string) (time.Time, string, error) {
 	parts := strings.SplitN(cursor, "|", 2)
diff --git a/backend/internal/validators/validators_test.go b/backend/internal/validators/validators_test.go
index e1ecad6..58fd6b1 100644
--- a/backend/internal/validators/validators_test.go
+++ b/backend/internal/validators/validators_test.go
@@ -76,3 +76,18 @@ func TestValidate_ValidStruct(t *testing.T) {
 	err := Validate.Struct(validStruct{Name: "hello"})
 	assert.NoError(t, err)
 }
+
+func TestIsValidSquareCheckoutID_AcceptsRealSquareID(t *testing.T) {
+	t.Parallel()
+	// Real Square checkout IDs are opaque UUIDs, not local 12-hex DB IDs.
+	assert.True(t, IsValidSquareCheckoutID("08YceKh7B3ZqO"))
+	assert.True(t, IsValidSquareCheckoutID("a1b2c3d4e5f6"))
+}
+
+func TestIsValidSquareCheckoutID_RejectsInvalid(t *testing.T) {
+	t.Parallel()
+	assert.False(t, IsValidSquareCheckoutID(""))
+	assert.False(t, IsValidSquareCheckoutID("../etc/passwd"))
+	assert.False(t, IsValidSquareCheckoutID("has spaces"))
+	assert.False(t, IsValidSquareCheckoutID("abc")) // too short
+}
diff --git a/frontend/src/lib/components/payments/PaymentModal.svelte b/frontend/src/lib/components/payments/PaymentModal.svelte
index a7f745c..9d0648f 100644
--- a/frontend/src/lib/components/payments/PaymentModal.svelte
+++ b/frontend/src/lib/components/payments/PaymentModal.svelte
@@ -67,9 +67,10 @@
 	let savedCardList = $state<
 		Array<{
 			id: string;
-			card_brand: string;
-			card_last4: string;
-			card_expiry: string;
+			brand: string;
+			last_4: string;
+			exp_month: number;
+			exp_year: number;
 			cardholder_name?: string;
 		}>
 	>([]);
@@ -559,13 +560,16 @@
 		}
 	}
 
-	// Saved cards
+	// Saved cards — fields match the backend SavedCard shape (brand, last_4,
+	// exp_month, exp_year), not the old card_brand/card_last4/card_expiry names
+	// which rendered blank.
 	let savedCards = $state<
 		Array<{
 			id: string;
-			card_brand: string;
-			card_last4: string;
-			card_expiry: string;
+			brand: string;
+			last_4: string;
+			exp_month: number;
+			exp_year: number;
 			cardholder_name?: string;
 		}>
 	>([]);
@@ -1183,11 +1187,11 @@
 											<rect x="1" y="4" width="22" height="16" rx="2" ry="2" />
 											<line x1="1" y1="10" x2="23" y2="10" />
 										</svg>
-										<span class="font-medium text-gray-900"
-											>{card.card_brand} ••••{card.card_last4}</span
-										>
+										<span class="font-medium text-gray-900">{card.brand} ••••{card.last_4}</span>
 									</div>
-									<span class="text-xs text-gray-500">{card.card_expiry}</span>
+									<span class="text-xs text-gray-500"
+										>{String(card.exp_month).padStart(2, '0')}/{card.exp_year}</span
+									>
 								</div>
 								{#if card.cardholder_name}
 									<div class="mt-1 text-xs text-gray-500">{card.cardholder_name}</div>
diff --git a/frontend/src/lib/square/square.ts b/frontend/src/lib/square/square.ts
index 804bd6d..aad0ea1 100644
--- a/frontend/src/lib/square/square.ts
+++ b/frontend/src/lib/square/square.ts
@@ -22,12 +22,18 @@ export function getSquareConfig(): SquareConfig | null {
 	return { appId: APP_ID, locationId: LOCATION_ID };
 }
 
+// Pinned SDK version: Square.js is loaded from the /v1/ path, which is
+// Square's stable major version. Square does not publish SRI hashes, so no
+// integrity attribute can be set — the /v1/ version pin is the supply-chain
+// control (S-3). Monitor Square's release notes before major bumps.
+const SQUARE_SDK_VERSION = 'v1';
+
 function sdkUrl(): string {
 	const env = (import.meta.env.VITE_SQUARE_ENVIRONMENT as string | undefined) ?? '';
 	const isSandbox = env === 'sandbox' || (APP_ID !== '' && APP_ID.startsWith('sandbox-'));
 	return isSandbox
-		? 'https://sandbox.web.squarecdn.com/v1/square.js'
-		: 'https://web.squarecdn.com/v1/square.js';
+		? `https://sandbox.web.squarecdn.com/${SQUARE_SDK_VERSION}/square.js`
+		: `https://web.squarecdn.com/${SQUARE_SDK_VERSION}/square.js`;
 }
 
 let sdkPromise: Promise<unknown> | null = null;
diff --git a/init-scripts/init-script.sql b/init-scripts/init-script.sql
index ec9b034..093014e 100644
--- a/init-scripts/init-script.sql
+++ b/init-scripts/init-script.sql
@@ -1984,7 +1984,9 @@ CREATE INDEX idx_user_saved_cards_active ON user_saved_cards(user_id, deleted_at
 CREATE TABLE refunds (
     id CHAR(12) PRIMARY KEY DEFAULT generate_refund_id(),
     payment_id CHAR(12) NOT NULL REFERENCES payments(id) ON DELETE CASCADE,
-    booking_id CHAR(12) NOT NULL REFERENCES bookings(id) ON DELETE CASCADE,
+    -- booking_id is NULL for non-booking payments (e.g. gift-card purchase
+    -- refunds); the payment row still links the refund via payment_id.
+    booking_id CHAR(12) REFERENCES bookings(id) ON DELETE CASCADE,
     amount NUMERIC(10,2) NOT NULL CHECK (amount > 0),
     square_refund_id TEXT,
     status payment_status NOT NULL DEFAULT 'pending',
diff --git a/obsidian/Crussell/Feature Catalog.md b/obsidian/Crussell/Feature Catalog.md
index d7e8352..3be681a 100644
--- a/obsidian/Crussell/Feature Catalog.md	
+++ b/obsidian/Crussell/Feature Catalog.md	
@@ -205,11 +205,11 @@ Multi-method payment system accepting Square (card terminal & online), cash, gif
 **Related:** [[Booking System|1. Booking System]] (completed bookings trigger tip eligibility), [[Today Page|7. Today Page]] (daily tips summary)
 
 ### 2.7 Refunds
-**What it does:** Admin processes refunds with automatic routing by payment method. Square card payments are refunded via Square API (post-DB-commit). Cash refunds are credited as gift card balance. Gift card payments are returned to the card's balance.
+**What it does:** Admin processes refunds with automatic routing by payment method. Square card payments are refunded via Square API (post-DB-commit). Cash refunds are credited as gift card balance. Gift card payments are returned to the card's balance. Refunds are resolved by Square's actual status (COMPLETED→completed, PENDING→left pending for the sweep, FAILED/REJECTED→failed) so an in-flight refund never blocks the over-refund guard. A background sweep (`sweep-pending-square-refunds`) retries/reconciles stuck refunds with a 23h age guard and surfaces failures as admin notifications.
 
 **Layman summary:** "If a booking is cancelled, the system automatically refunds the right amount to the right place."
 
-**Related:** [[Cancellation|1.11 Cancellation]], [[Refund to Gift Card|4.11 Refund to Gift Card]]
+**Related:** [[Cancellation|1.11 Cancellation]], [[Refund to Gift Card|4.11 Refund to Gift Card]], [[Background Jobs|13. Background Jobs]] (refund sweep)
 
 ### 2.8 Payment Split Logic (`buildSplitRecords`)
 **What it does:** When a customer pays online, a single Square charge is automatically split into up to 3 records: deposit portion (first 50%), balance portion (remaining owed), and tip portion (overflow beyond the total). This protects the deposit accounting.
@@ -219,11 +219,11 @@ Multi-method payment system accepting Square (card terminal & online), cash, gif
 **Related:** [[Deposit System|1.2 Deposit System]], [[Tips|2.6 Tips]]
 
 ### 2.9 Double-Payment Prevention
-**What it does:** Two mechanisms prevent accidental double-charges: PostgreSQL advisory locks (serialize payment attempts per-booking at the database level) and idempotency keys (client-generated unique IDs).
+**What it does:** Two mechanisms prevent accidental double-charges: PostgreSQL advisory locks (serialize payment attempts per-booking at the database level) and idempotency keys (client-generated unique IDs, or deterministic keys derived from booking+type+amount+card for the admin saved-card path). Same-key retries reuse the original pending record instead of charging again. A background sweep fails stale pending payments older than Square's ~24h key-retention window, so a late retry is cleanly rejected rather than issuing a second charge.
 
 **Layman summary:** "If you open two tabs and try to pay twice, only one payment goes through."
 
-**Related:** [[Idempotency Keys|1.12 Idempotency Keys]], [[Idempotent Purchases|4.10 Idempotent Purchases]]
+**Related:** [[Idempotency Keys|1.12 Idempotency Keys]], [[Idempotent Purchases|4.10 Idempotent Purchases]], [[Background Jobs|13. Background Jobs]] (stale-pending sweep)
 
 ### 2.10 VAT Calculation
 **What it does:** Applies VAT to payments and till sales based on business settings (rate, registration status, SPV/MPV voucher type). Discount, on-the-house, and tip payments are exempt.
@@ -473,7 +473,7 @@ The central management hub for salon operations — managing users, bookings, se
 **Related:** [[Patch Tests|1.6 Patch Tests]], [[Services Catalog|1.5 Services Catalog]]
 
 ### 5.9 Till Purchases (POS)
-**What it does:** Point-of-sale interface for selling gift cards at the counter (cash, card machine, saved card, online card entry, on the house).
+**What it does:** Point-of-sale interface for selling gift cards at the counter (cash, card machine, saved card, online card entry, on the house). The saved-card path charges the customer's card-on-file directly via Square (pending-first, deterministic idempotency key, advisory lock per booking); card-machine sales create a Square Terminal checkout and are completed by polling. Pending card till-sales are failed by the stale-pending sweep after Square's ~24h key-retention window.
 
 **Layman summary:** "Sell gift cards at the till — take cash or card."
 
@@ -842,7 +842,7 @@ The platform infrastructure — Docker Compose stack, CI/CD, local development e
 
 ## 13. Background Jobs (Cron Scheduler)
 
-A centralized cron scheduler that runs 20 maintenance jobs for cleanup, transitions, and data management.
+A centralized cron scheduler that runs 22 maintenance jobs for cleanup, transitions, and data management.
 
 **Related:** [[Availability & Scheduling|3. Scheduling]] (hours apply), [[GDPR & Compliance|9. GDPR & Compliance]] (cleanup), [[Gift Cards|4. Gift Cards]] (expiry/cleanup), [[Payments|2. Payments]] (idempotency cleanup)
 
@@ -851,8 +851,10 @@ A centralized cron scheduler that runs 20 maintenance jobs for cleanup, transiti
 - **cleanup-expired-deposits**: Move unpaid bookings to `pending_release` state
 - **cleanup-rate-limiters**: Purge stale rate limiter entries
 - **cleanup-gdpr-export-cache**: Expire old GDPR export caches
+- **sweep-pending-square-refunds**: Reconcile/retry stuck Square refunds (23h age guard; aggregates per charge, single refund per charge, resolves by Square status, notifies on failure) — starts on the `:00` ticks
+- **sweep-stale-pending-payments**: Fail stale pending payments and till-sales older than Square's ~24h idempotency-key retention, so a late retry is cleanly rejected instead of issuing a second charge — starts on the `:01` ticks, offset one minute from the refund sweep to avoid table contention
 
-**Related:** [[Slot Reservation TTLs|1.14 Slot Reservation TTLs]], [[Deposit System|1.2 Deposit System]]
+**Related:** [[Slot Reservation TTLs|1.14 Slot Reservation TTLs]], [[Deposit System|1.2 Deposit System]], [[Payments|2. Payments]] (refund sweeps, stale-pending payment sweep)
 
 ### 13.2 Every Minute
 - **cleanup-progressive-rate-limiter**: Clean progressive rate limiter state
diff --git a/obsidian/Crussell/Future Work - Gap Backlog.md b/obsidian/Crussell/Future Work - Gap Backlog.md
index 067d6f3..fad19fa 100644
--- a/obsidian/Crussell/Future Work - Gap Backlog.md	
+++ b/obsidian/Crussell/Future Work - Gap Backlog.md	
@@ -1,10 +1,10 @@
 # Future Work — Gap Backlog
 
-**Last Updated:** July 2026
+**Last Updated:** August 2026
 **Status:** Living backlog — add to this as gaps are discovered
 **Previous version:** OUT OF DATE — this replaces the prior document. Completed items removed, new items added from exhaustive codebase audit.
 
-This document has three lists: **Pre-Launch** (integration tasks), **MVP** (missing features for daily ops), **Stretch** (nice-to-have). Items are numbered sequentially. All done items are removed without tracking.
+This document has three lists: **Pre-Launch** (integration tasks), **MVP** (missing features for daily ops), **Stretch** (nice-to-have). Items are numbered sequentially. All done items are removed without tracking (see "Previously Completed" sections).
 
 ### Development Context
 
@@ -25,17 +25,16 @@ These are things that work fine in dev (with mocks) but need real implementation
 
 | # | Task | Effort | Area | Dev Status | Notes |
 |---|---|---|---|---|---|
-| P1 | **Square payments: wire prod client alongside dev mock** | XL (5-7d) | Backend | ✅ **COMPLETED Aug 2026** — `internal/square/square_http_client.go` implements the real REST client (payments, terminal checkouts, refunds, cards, list-refunds). Prod client (`internal/square/square.go`) and dev `devProdClient` (`square_dev.go`) both call real Square when `SQUARE_ENVIRONMENT=sandbox|production`; `mock` uses the in-memory client. The health endpoint reports `"mock"`/`"ok"` accordingly (was `"not_implemented"`). | |
 | P2 | **S3/R2 storage: implement prod side of the abstraction** | M (2-3d) | Backend | Dev works (`internal/s3/s3_dev.go` — RustFS + in-memory fallback). Prod side (`internal/s3/s3.go:52-62`) returns "not implemented" for Upload/Download/Delete. The prod `S3Client` struct lacks the `*s3.Client` field entirely — it was never populated. | The storage abstraction was defined early and the dev side got a full implementation. The prod side needs the AWS SDK v2 dependency and real S3/R2 calls. Portfolio images and profile pictures will start working in prod once this is done. |
 | P3 | **Square webhook event handling: from log-only to action** | S (1d) | Backend | Webhook signature verification works (HMAC-SHA256, references Square docs). Event parsing works. But `handlePaymentUpdated` and `handleRefundUpdated` (`square.go:88-94`) only log the event data — they never update booking/payment state. | The webhook receiver was built first (parse + verify). The handlers that act on events were deferred. Now they need to: update payment status on `payment.updated`, update refund status on `refund.updated`. |
-| P4 | **Payment reconciliation: add recovery for split-brain scenarios** | L (3-5d) | Backend | 11 `log.Printf("CRITICAL: ... manual reconciliation required")` calls exist across payment, refund, and till handlers. When Square succeeds but the DB transaction fails afterwards, state diverges with no automated recovery. | This happens when the application correctly processes a Square payment but then hits a DB error on commit. In dev, this was handled by just logging it. For prod, we need a reconciliation job or retry mechanism. |
+| P4 | **Payment reconciliation: add recovery for split-brain scenarios** | L (3-5d) | Backend | 20 `log.Printf("CRITICAL: ... manual reconciliation required")` calls exist across payment, refund, and till handlers. When Square succeeds but the DB transaction fails afterwards, state diverges with no automated recovery. | This happens when the application correctly processes a Square payment but then hits a DB error on commit. In dev, this was handled by just logging it. For prod, we need a reconciliation job or retry mechanism. (Count grew from 18 to 20 with the stale-pending sweep's manual-reconciliation warnings in the Aug 2026 review round.) |
 | P5 | **Till Purchases: wire the backend payment flow** | M (1d) | Frontend + Backend | Frontend (`TillPurchases.svelte:203-208`) has the UI built but the Charge button is disabled with "Payment flow and backend integration coming soon." The till sale submission path was deferred. | The till UI is fully designed — service selection, gift card types, payment method selection. Only the final "submit payment" path was left as a placeholder. Needs the backend `till.go` sale endpoint wired. |
 | 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 | ✅ 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: re-enable new-card entry with nonce-based flow** | S-M (2-3d) | Frontend | ✅ **COMPLETED Aug 2026** — `SquareCardInput.svelte` tokenizes cards to `cnon:` nonces via the Web Payments SDK (env-gated on `VITE_SQUARE_APPLICATION_ID`/`VITE_SQUARE_LOCATION_ID`); all 8 flows re-enabled (tips ×3, booking payment, deposit, Buy a Gift Card, account Add Card, till `online_square`); `CardEntryUnavailable` kept only as the no-credentials fallback. See `plans/p11-square-web-payments-sdk.md`. | |
+| P12 | **Square sandbox smoke test (pre-go-live gate)** | S-M (1d, once credentials available) | E2E | **BLOCKED — no real Square credentials available.** Must exercise the real API path end-to-end: new-card tokenization → payment → saved card → refund → reconcile, against Square's sandbox. Also verifies the M-8 open question (is `card.customer_id` enforced as Required?). | The dev mock cannot exercise Square's real wire contract (key-length limits, `device_options`, refund statuses, error codes). This is the sole remaining item before the production flip. See `plans/p11-square-web-payments-sdk.md` Remaining Items. |
+| P13 | **Reconcile deterministically-keyed saved-card charges** | S (2-3h) | Backend | **Deferred — deliberate trade-off (N-OBS-1).** The admin "Charge Saved Card" idempotency key `bookingID-sc-type-amount-cardID` dedups two *identical* repeat charges on one booking. Not UI-reachable today (PaymentModal always sends the current `totalDue`, which changes after each charge). | Revisit if the admin flow ever gains a "charge exact amount twice" path — the key would then need a client nonce or attempt counter. Tracked from the final payment review. |
 
 ---
 
@@ -50,7 +49,6 @@ These are missing functionality that prevents daily operations, legal compliance
 | M3 | **Email verification calls wrong API endpoint** | S (2h) | Frontend | `+layout.svelte:33` calls `/api/verify-email` which 404s. Correct endpoints: `POST /api/verify/generate` and `POST /api/verify/check`. Every login triggers a silent failure. |
 | M4 | **CSRF protection** | S (2-3h) | Backend | SvelteKit handles CSRF for its own forms, but direct API calls to `/api/*` bypass it. |
 | M5 | **XSS input sanitization** | S (2-3h) | Backend | Backend validates format (regex, length) but doesn't sanitize HTML entities in stored fields. CSP mitigates but doesn't eliminate risk. |
-| M6 | **Square webhook signature verification — enforce always** | S (1-2h) | Backend | Currently skips if `SQUARE_WEBHOOK_SIGNATURE_KEY` is empty. Prod must always verify. Implementation exists (HMAC-SHA256), just needs enforcement. |
 | M7 | **Booking cancellation UI from user account** | S (2-3h) | Frontend | `UserBookingModal` shows details but has no cancel button. Backend `DELETE /api/bookings/{id}` exists. |
 | M8 | **Business settings management UI** | M (1-2d) | Frontend | `GET/PUT /api/admin/settings` endpoints exist. No admin page — staff use curl or SQL. |
 | M9 | **CSV/Excel export for bookings/payments** | M (1d) | Backend | No endpoint for accounting software export. SQL functions exist but not wired. |
@@ -98,21 +96,28 @@ These don't add features but reduce maintenance cost and risk.
 | T4 | **Create or remove documented `update_data_consent()` function** | S (1h) | DB Schema | Listed in FUNCTION USAGE SUMMARY comment (~line 2401) but no `CREATE FUNCTION` exists. |
 | T5 | **Resolve 2 route-conflicted lint-ignored handlers** | S (1h) | Backend | `manage.go:27,314` — handlers exist only for tests but routes conflict. |
 | T6 | **Resolve portfolio lint-ignored handler** | S (1h) | Backend | `images.go:53` — handler referenced from tests only, never routed. |
-| T7 | **Fix README job count: 20 not 21** | S (5min) | Docs | README says "21 maintenance jobs", code registers 20. |
+| T7 | **Fix README job count: 22 not 21** | S (5min) | Docs | ✅ **COMPLETED Aug 2026** — README updated to 22 maintenance jobs (the two payment sweeps added in the review round: `sweep-pending-square-refunds`, `sweep-stale-pending-payments`). |
 | T8 | **Audit 18 silent catch blocks** | M (1d) | Frontend | 1 `catch (e) {}`, 17 `catch (_err)` — errors swallowed silently. Many should show user-facing toasts. |
 | T9 | **33 `svelte/no-navigation-without-resolve` suppressions** | M (1d) | Frontend | Create a project-wide `goto` wrapper instead of suppressing per-file. |
 | 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 | ✅ 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. |
+| T14 | **Error tracking / monitoring (Sentry)** | M (1-2d) | Backend | `log.Printf()` only. No alerting on 5xx. 39 ALERT + 20 CRITICAL logs will never be seen. |
 
 ---
 
+## Previously Completed Items (August 2026 backlog)
+
+- ~~**Square payments: wire prod client alongside dev mock (P1)** — `internal/square/square_http_client.go` implements the real REST client (payments, terminal checkouts, refunds, cards, list-refunds). Prod client (`internal/square/square.go`) and dev `devProdClient` (`square_dev.go`) both call real Square when `SQUARE_ENVIRONMENT=sandbox|production`; `mock` uses the in-memory client. The health endpoint reports `"mock"`/`"ok"` accordingly (was `"not_implemented"`).~~
+- ~~**Square Web Payments SDK: re-enable new-card entry with nonce-based flow (P11)** — `SquareCardInput.svelte` tokenizes cards to `cnon:` nonces via the Web Payments SDK (env-gated on `VITE_SQUARE_APPLICATION_ID`/`VITE_SQUARE_LOCATION_ID`); all 8 flows re-enabled (tips ×3, booking payment, deposit, Buy a Gift Card, account Add Card, till `online_square`); `CardEntryUnavailable` kept only as the no-credentials fallback. See `plans/p11-square-web-payments-sdk.md`.~~
+- ~~**Square webhook signature verification — enforce always (M6)** — the webhook handler is now **fail-closed**: rejects with 503 when `SQUARE_WEBHOOK_SIGNATURE_KEY` is unset and 403 when the signature header is missing/invalid (`handlers/webhooks/square.go`).~~
+- ~~**Fix README job count (T7)** — README updated to 22 maintenance jobs.~~
+- ~~**Fix `devProdClient` rune-arithmetic in test (T13)** — `rune('0'+idx)` replaced with `fmt.Sprintf("concurrent-key-%d", idx)`.~~
+
 ## 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)`.~~
+- ~~**Tip payments: replace placeholder card tokens (P9)** — `card_token: 'placeholder'` replaced with real saved card selection + CardInput with Luhn/expiry/CVC validation across all 3 tip pages. CardBrandIcon SVGs added for all Square-supported brands.~~
 
 ## Previously Completed Items (June 2026 backlog)
 
diff --git a/obsidian/Crussell/Overview.md b/obsidian/Crussell/Overview.md
index 569bd90..c3e9d31 100644
--- a/obsidian/Crussell/Overview.md
+++ b/obsidian/Crussell/Overview.md
@@ -34,7 +34,7 @@ Square integration has two build-tagged implementations:
 - **Dev** (`//go:build dev`): Mock client simulates async checkout with polling. No real payments.
 - **Prod** (`//go:build !dev`): Connects to live Square API. Requires Square credentials in `.env`.
 
-Saved cards stored in `user_saved_cards` with soft delete (`retained_until` for 7-year UK compliance). Refunds tracked in `refunds` table — partial or full. Square webhooks at `/api/webhooks/square` receive payment/refund events (HMAC-verified; currently log-only — status is tracked via the synchronous + sweep/reconcile paths, backlog P3).
+Saved cards stored in `user_saved_cards` with soft delete (`retained_until` for 7-year UK compliance). Refunds tracked in `refunds` table — partial or full. Square webhooks at `/api/webhooks/square` receive payment/refund events (HMAC-verified **fail-closed** — 503 without the signing key, 403 on bad signature; currently log-only — status is tracked via the synchronous + sweep/reconcile paths, backlog P3).
 
 Fees column on `payments` stores actual Square deductions. `square_deposits` table for bank reconciliation (matching batch deposits to Mettle account).
 
@@ -53,7 +53,7 @@ Expiry is 24 months from last use (not from purchase). Each use resets the timer
 
 Accounts idle 2+ years (no balance) or 5+ years (with balance) are anonymized. Balances before deletion move to `gift_card_expired_balances`. `CleanupIdleAccounts()` runs on availability fetch.
 
-VAT treatment: gift cards are Single-Purpose Vouchers (SPVs) by default — VAT charged at purchase, not redemption. Configurable to Multi-Purpose Voucher (MPV) in business settings. Gift card purchases now insert a pending payment record with VAT applied before calling Square — the DB transaction commits first, so Square failures leave a retryable pending record rather than losing the payment.
+VAT treatment: gift cards are Single-Purpose Vouchers (SPVs) by default — VAT charged at purchase, not redemption. Configurable to Multi-Purpose Voucher (MPV) in business settings. Gift card purchases now insert a pending payment record with VAT applied before calling Square — the DB transaction commits first, so Square failures leave a retryable pending record rather than losing the payment. Two background sweeps close Square's ~24h idempotency-key retention window: `sweep-pending-square-refunds` reconciles/retries stuck refunds, and `sweep-stale-pending-payments` fails stale pending payments and till-sales so a late retry cannot issue a second charge.
 
 ### Scheduling
 
@@ -87,7 +87,7 @@ Campaign lifecycle: `draft → active → completed` (or any → `cancelled`, `a
 
 ### Compliance
 
-**GDPR Article 15**: Full data export via `/gdpr` frontend. Async Go endpoint (`GET /api/user/gdpr-export`) with 12h in-memory cache and background generation (navigation away doesn't cancel). 21-section JSON export: user profile, bookings with overrides, payments, refunds, saved cards, social logins, loyalty redemptions, booking discounts, edit requests, affiliate payouts, forgiven no-shows, patch tests, referrals, referral discounts, notification preferences, gift_card_balance, gift_card_transactions, gift_cards, admin_audit_log, login_audit, refresh_tokens, name_history, export metadata. **Verification codes excluded** (authentication tokens are not personal data under GDPR Art 15). Frontend: skeleton loading, 2s polling, styled report cards/tables, PDF export (print CSS hides navbar + verification banner), raw JSON download.
+**GDPR Article 15**: Full data export via `/gdpr` frontend. Async Go endpoint (`GET /api/user/gdpr-export`) with 12h in-memory cache and background generation (navigation away doesn't cancel). 23-section JSON export: user profile, bookings with overrides, payments, refunds, saved cards, social logins, loyalty redemptions, booking discounts, edit requests, affiliate payouts, forgiven no-shows, patch tests, referrals, referral discounts, notification preferences, gift_card_balance, gift_card_transactions, gift_cards, admin_audit_log, login_audit, refresh_tokens, name_history, export metadata. **Verification codes excluded** (authentication tokens are not personal data under GDPR Art 15). Frontend: skeleton loading, 2s polling, styled report cards/tables, PDF export (print CSS hides navbar + verification banner), raw JSON download.
 
 **Account deletion**: Registered users → `anonymize_user()` SQL function extended with child table PII scrubbing (social logins deleted, saved cards soft-deleted with PCI data cleared, verification codes expired, time blocker reservations scrubbed including `RESERVATION:edit_request:%` entries, edit request notes nulled, notification preferences deleted). External system scrubbing: S3 profile picture, Square saved cards. Guests → `delete_guest_user()` for full removal.
 
diff --git a/obsidian/Crussell/Technical Manual.md b/obsidian/Crussell/Technical Manual.md
index 3ac0045..7d85a1e 100644
--- a/obsidian/Crussell/Technical Manual.md	
+++ b/obsidian/Crussell/Technical Manual.md	
@@ -64,7 +64,7 @@ Backend (:8080)
 | `handlers/auth` | local.go, social.go | Registration (with referral code validation), login, refresh, email verification |
 | `handlers/bookings` | bookings.go, reserve.go, manage.go, admin_reserve.go, cancel_reservation.go, admin_cancel_reservation.go, closing_time.go | Booking CRUD, reservations with **self-blocking prevention** (`excludeUserID` parameter on `CheckTimeBlockerOverlap` + pre-overlap DELETE with IP hash anon cleanup), admin management, edit requests, discounts, closing hours validation (`checkClosingHours` + `getClosingTimeForDate` resolves staged default hours for bookings), active booking limits, GetBookingsByCreatedRange, created_by_name resolution, **explicit reservation cancellation** (`DELETE /api/bookings/reserve` for users, `DELETE /api/admin/bookings/reserve` for admin walk-in/call-in) |
 | `handlers/payments` | handlers.go, service.go, validators.go, giftcards.go, till.go, refunds.go, refund_policy.go | Square payments: terminal, online, refunds, tips, saved cards, gift cards (CRUD, topup, transfer, redeem, buy, expired balances, till sales). Refund calculation with notice-period tiers and deposit protection |
-| `handlers/webhooks` | square.go | Square webhook handler for payment status updates. **Fail-closed signature check** — rejects requests with 403 when `SQUARE_WEBHOOK_SIGNATURE_KEY` is set but header is missing. Dev mode: skips verification when env var is empty. HMAC-SHA256 signature verified per Square spec (base64 output, `x-square-hmacsha256-signature` header, notificationURL + body). `payment.updated`/`refund.updated` events are currently **log-only** (backlog P3 — status flows through the synchronous + sweep/reconcile paths instead). |
+| `handlers/webhooks` | square.go | Square webhook handler for payment status updates. **Fail-closed signature check** — rejects with 503 when `SQUARE_WEBHOOK_SIGNATURE_KEY` is unset, and 403 when the `x-square-hmacsha256-signature` header is missing or invalid. HMAC-SHA256 signature verified per Square spec (base64 output, notificationURL + body). `payment.updated`/`refund.updated` events are currently **log-only** (backlog P3 — status flows through the synchronous + sweep/reconcile paths instead). |
 | `handlers/admin` | users.go, analytics.go, custom_services.go, discount_campaigns.go, settings.go | Admin user management, custom services CRUD (list/create/get/update/promote/delete), discount campaigns, analytics (stub), business settings (GET/PUT with VAT, gift card config) |
 | `handlers/today` | today.go | Current/next appointment, today's grid, pending approvals, `DoneForDay` state with daily/weekly summary (`DailySummary` with `total_bookings`, `customers_served`, `summary_scope`), auto-status transitions, closed-day aggregation via `findWeekSummaryRange` + `computeAggregateSummary`. Exceptional hours lookup uses `exceptional_group_applications.week_start` (0=Monday). |
 | `handlers/user` | profile.go, account.go, guest.go, loyalty.go, customer_relationship.go, gdpr_export.go | User profile, guest creation (with CheckEmailHandler for registered-email detection), loyalty, contact info, GDPR export (async with 12h cache) |
@@ -259,7 +259,7 @@ Added in the June 2026 security pass:
 | Fix | File | Description |
 |-----|------|-------------|
 | Removed verification code logging | `handlers/auth/local.go:545` | Deleted `log.Printf("DEBUG: Verification code for %s: %s ...")` — was leaking verification codes to stdout |
-| Webhook signature fail-closed | `handlers/webhooks/square.go:59-69` | Changed from "skip verification if header missing" to "reject 403 if key set but header missing" |
+| Webhook signature fail-closed | `handlers/webhooks/square.go:34-60` | Webhook verification is fully **fail-closed**: 503 when `SQUARE_WEBHOOK_SIGNATURE_KEY` is unset (a misconfigured deployment must not silently accept forged events), 403 when the signature header is missing or invalid. Previously it skipped verification when the key was empty. |
 | S3 delete error checking | `handlers/portfolio/images.go:975` | Changed `s3.Client.Delete(...)` (ignored return) → `if err := s3.Client.Delete(...); err != nil { log.Printf(...) }` |
 
 CORS uses `*` in local dev. In production behind Cloudflare, nginx handles CORS. No CSP violations expected — the SvelteKit SPA doesn't load external scripts or fonts.
@@ -417,7 +417,7 @@ CORS uses `*` in local dev. In production behind Cloudflare, nginx handles CORS.
 | `payment_type` | `deposit`, `full`, `tip`, `balance`, `partial` |
 | `payment_method` | `online_square`, `in_person_card`, `cash`, `giftcard`, `discount`, `on_the_house` |
 | `payment_status` | `pending`, `completed`, `failed`, `refunded` |
-| `admin_notification_reason` | `pending_booking`, `cancelled_booking`, `rescheduled_booking`, `1_week_no_pay`, `1_month_no_pay`, `affiliate_claim`, `late_cancellation`, `no_deposit`, `deposit_paid`, `edit_request`, `new_booking`, `edit_requested`, `deposit_not_paid_by_deadline`, `default_hours_changed` |
+| `admin_notification_reason` | `pending_booking`, `cancelled_booking`, `rescheduled_booking`, `1_week_no_pay`, `1_month_no_pay`, `affiliate_claim`, `late_cancellation`, `no_deposit`, `deposit_paid`, `edit_request`, `new_booking`, `edit_requested`, `deposit_not_paid_by_deadline`, `default_hours_changed`, `gift_card_purchased_for_friend`, `refund_failed` |
 | `campaign_type` | `time_based`, `milestone` |
 | `milestone_type` | `per_user_booking_count`, `global_booking_count`, `anniversary` |
 | `milestone_unit` | `bookings`, `months`, `years` |
@@ -450,7 +450,7 @@ CORS uses `*` in local dev. In production behind Cloudflare, nginx handles CORS.
 | `forgiven_no_shows` | Tracks no-shows forgiven by admin (booking_id, forgiven_by FK to users, created_at). Used by `CountUnforgivenNoShows()` to exclude forgiven records |
 | `payments` | Payment transactions (VAT fields, invoice_number sequence, fees column for Square deductions, saved_card_id, gift_card_id) |
 | `user_saved_cards` | Saved card details (square_card_id, brand, last4, fingerprint, soft delete with retained_until) |
-| `refunds` | Refund records linked to bookings (amount, reason, square_refund_id, created_by FK to users, ON DELETE SET NULL) |
+| `refunds` | Refund records linked to a payment (amount, reason, `square_refund_id`, `refund_attempts` int, `origin` manual|cancellation, `idempotency_key` unique, `created_by` FK to users, ON DELETE SET NULL; `booking_id` is nullable — NULL for non-booking payments such as gift-card purchase refunds) |
 | `financial_aggregates` | Monthly aggregated financial statistics (no PII) — populated when granular records expire |
 | `square_deposits` | Square deposit batch tracking for bank reconciliation (batch_id, total_amount, deposited_at) |
 | `affiliate_payouts` | Affiliate commission tracking |
@@ -481,7 +481,7 @@ CORS uses `*` in local dev. In production behind Cloudflare, nginx handles CORS.
 | `generate_referral_code()` | 12-char referral code with collision detection |
 | `anonymize_user(target_id)` | GDPR right-to-be-erased for registered users — child table PII scrubbing |
 | `delete_guest_user(target_id)` | Full removal of guest account |
-| `export_all_user_data(target_user_id)` | GDPR Article 15 SAR — 21-section JSON export (excludes verification_codes; includes admin_audit_log, gift_cards, name_history) |
+| `export_all_user_data(target_user_id)` | GDPR Article 15 SAR — 23-section JSON export (excludes verification_codes; includes admin_audit_log, gift_cards, name_history) |
 | `get_vat_return_data(start, end)` | VAT return summary for MTD. **Updated:** Now includes `till_sales` via `UNION ALL` — till sales (gift cards, merchandise, services) are counted alongside booking payments for VAT reporting. |
 | `export_sales_transactions(start, end, include_vat)` | Tax-compatible transaction export. **Updated:** Uses dynamic `vat_rate` from the `payments` table (or `business_settings.default_vat_rate`) instead of hardcoded 1.20. |
 | `get_monthly_business_summary(start, end)` | Monthly revenue breakdown |
@@ -1807,7 +1807,7 @@ FROM bookings b LEFT JOIN payments p ON p.booking_id = b.id WHERE b.user_id = $1
 | Frequency | Jobs | Cron |
 |-----------|------|------|
 | Every min | Progressive rate limiter cleanup | `* * * * *` |
-| Every 5 min | Reservation cleanup, expired deposits, rate limiter cleanup, GDPR cache cleanup | `*/5 * * * *` |
+| Every 5 min | Reservation cleanup, expired deposits, rate limiter cleanup, GDPR cache cleanup, **refund sweep** (`sweep-pending-square-refunds`), **stale-pending payment/till-sale sweep** (`sweep-stale-pending-payments`, offset +1 min) | `*/5 * * * *` |
 | Hourly | Loyalty redemptions, idempotency keys, revoked JTIs, stale login entries, discount campaign auto-transition | `0 * * * *` |
 | Daily 7am | Unpaid booking notifications (1-week and 1-month overdue) | `0 7 * * *` |
 | Daily 2am | Expired verification codes, expired/revoked refresh tokens | `0 2 * * *` |
diff --git a/obsidian/Crussell/plans/p11-square-web-payments-sdk.md b/obsidian/Crussell/plans/p11-square-web-payments-sdk.md
index 5e5633d..961787f 100644
--- a/obsidian/Crussell/plans/p11-square-web-payments-sdk.md
+++ b/obsidian/Crussell/plans/p11-square-web-payments-sdk.md
@@ -1,6 +1,6 @@
 # P11 — Square Web Payments SDK Implementation Plan
 
-**Status:** ✅ COMPLETE (implemented August 2026 — all 8 flows re-enabled; new-card entry tokenized via `cnon:` nonces)
+**Status:** ✅ COMPLETE — IMPLEMENTED (August 2026). All 8 flows re-enabled; new-card entry tokenized via `cnon:` nonces. Two follow-up items remain intentionally open (see [Remaining Items](#remaining-items--why-deferred) — both require real Square credentials and gate the production flip).
 **Owner:** Agent implementing P11 (Square Web Payments SDK)
 **Estimated effort:** 2-3 days (backend groundwork already landed; this is now a frontend-only integration)
 **Backlog reference:** `Future Work - Gap Backlog.md` item P11
@@ -109,13 +109,27 @@ All 8 flows render `SquareCardInput` and send the resulting `cnon:xxx` as `new_c
 
 ---
 
-## Definition of Done (ALL COMPLETE)
+## Definition of Done
 
+### Completed (all verified in the final review round)
 - [x] Square Web Payments SDK loads (sandbox + prod URLs, env-gated)
 - [x] `SquareCardInput` tokenizes cards → `cnon:xxx`
 - [x] All 8 flows re-enabled to send nonces, not PANs (tip ×3, booking payment, deposit, Buy a Gift Card, account Add Card, admin till `online_square`)
 - [x] `CardEntryUnavailable` kept only as the no-credentials fallback
 - [x] Backend nonce paths verified unchanged (Step 4/5 done)
 - [x] Frontend checks pass: svelte-check 0 errors, eslint 0 errors, build succeeds
-- [ ] Sandbox smoke test (BLOCKED — no real Square credentials available; must run before any production flip): new-card tokenization → payment → saved card → refund → reconcile, exercised against a real Square endpoint
 - [x] Docs updated (README, Gap Backlog, Feature Catalog, Technical Manual)
+
+## Remaining Items & Why Deferred
+
+> Both items below require **real Square credentials** (sandbox or production). They cannot be exercised against the dev mock — the mock does not enforce Square's real wire contract. They are the **sole gate on the production flip** and are tracked as open backlog items.
+
+| # | Item | Why deferred |
+|---|---|---|
+| R1 | **Sandbox smoke test** — new-card tokenization → payment → saved card → refund → reconcile, exercised against a real Square endpoint | **BLOCKED — no real Square credentials available.** The full end-to-end path (Web Payments SDK nonce → `POST /v2/cards` → `POST /v2/payments` → refund → `ListRefunds` reconcile) can only be validated against Square's sandbox. Must run before any production flip. |
+| R2 | **M-8 open question: is `card.customer_id` enforced as Required at runtime?** | The app deliberately omits `customer_id` (no Square customer provisioning — linkage uses `reference_id`). Square's API reference documents `customer_id` as Required, but integrations report cards can be created without it. If a sandbox `POST /v2/cards` 400s with `MISSING_REQUIRED_PARAMETER`, the app must provision Square customers before go-live. Gated on the same sandbox credentials as R1. |
+| R3 | **N-OBS-1: saved_card deterministic idempotency key dedups identical repeat charges** | **Deliberate, accepted trade-off** (not a credential blocker). The admin "Charge Saved Card" key `bookingID-sc-type-amount-cardID` means two *identical* charges on one booking dedup to the first. Not UI-reachable today (PaymentModal always sends the current `totalDue`, which changes after a charge), and the double-click protection is worth more than a hypothetical "charge exact amount twice" path. Flagged for revisit in the Gap Backlog if that path ever appears. |
+
+---
+
+*Plan record — implementation complete. Remaining items require external credentials and are the pre-go-live gate.*