Sweep lost-response charges by idempotency-key replay (22h cutoff, rescue/fail/WARN)

The stale-pending sweep now runs two passes. Pass 1 (22h cutoff — deliberately
2h earlier than the 24h legacy cutoff) targets pending rows with a STORED
idempotency key but NO square_payment_id: the lost-response case, where the
charge may have completed at Square with the response never received. Each row
is reconciled at Square by replaying the key (ReplayPaymentByKey): a COMPLETED
charge is rescued to 'completed' with the real square_payment_id written back,
a charge Square proves never happened is failed (till-sale gift-card clawback
included), an ambiguous answer leaves the row pending for the next run. The
earlier cutoff keeps the replay inside Square's ~24h key-retention window;
replaying at exactly 24h risks an expired key misreading as 'never charged'.

Pass 2 (legacy 24h cutoff) reconciles rows WITH a square_payment_id by payment
id; rows with neither payment id nor stored key (no reconcile possible) are
failed with a WARN that the charge outcome is unknown. Late retries on all
swept rows are rejected (409), preventing a second Square charge.

backend/handlers/payments/sweep.go

@@ -6,6 +6,7 @@ import (
 	"errors"
 	"fmt"
 	"log"
+	"math"
 	"strings"
 	"time"
 
@@ -31,43 +32,90 @@ import (
 // 'failed' with no automatic resolution — the money would otherwise be lost
 // in limbo (MINOR-R3). Reconciliation is deliberately minimal: status +
 // updated_at only, no split/VAT recomputation (that is the handler's job; the
-// row is >24h stale and this is a reconciliation rescue).
+// row is >24h stale and this is a reconciliation rescue). A row with NO
+// square_payment_id but a STORED idempotency key (the lost-response case — the
+// charge may have completed at Square with the response never received) is
+// reconciled at Square by replaying the key (ReplayPaymentByKey) at an EARLIER
+// 22h cutoff, while the key is still inside Square's ~24h retention window: a
+// COMPLETED charge is rescued to 'completed' with the real square_payment_id
+// written back, and a charge Square proves never happened is failed. Rows with
+// neither a square_payment_id nor a stored key cannot be reconciled and are
+// failed with a WARN exactly as the legacy sweep did.
 //
 // 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.
 const stalePendingPaymentAge = 24 * time.Hour
 
+// stalePendingKeyedAge is how old a pending row with a stored idempotency key
+// (but no square_payment_id — the lost-response case) must be before the sweep
+// reconciles it at Square by replaying the key. It is deliberately 2h EARLIER
+// than stalePendingPaymentAge so the replay lands comfortably inside Square's
+// ~24h idempotency-key retention window: replaying at exactly 24h risks the key
+// already having expired, and an expired key would make the probe rejection
+// look like "never charged" even when the charge actually landed. Rows older
+// than stalePendingPaymentAge when swept can no longer be replayed
+// trustworthily and fall back to the legacy blind-fail + WARN.
+const stalePendingKeyedAge = 22 * time.Hour
+
 func SweepStalePendingPayments(ctx context.Context) (int, error) {
 	cutoff := clock.Now().Add(-stalePendingPaymentAge)
+	keyedCutoff := clock.Now().Add(-stalePendingKeyedAge)
 
-	payCount, payCompleted, err := sweepStaleRows(ctx, "payments", cutoff)
+	// Pass 1 (earlier cutoff): rows with a stored idempotency key but NO
+	// square_payment_id are the lost-response case — the charge may have landed
+	// at Square with the response lost. They are reconciled at Square by
+	// replaying the key (ReplayPaymentByKey) while the key is still inside
+	// Square's ~24h retention window: a COMPLETED charge is rescued to
+	// 'completed' with the real square_payment_id, a charge Square proves never
+	// happened is failed (and a till sale's funded gift card clawed back), an
+	// ambiguous answer leaves the row pending for the next run, and a row
+	// already past the retention window is blind-failed with a WARN exactly as
+	// the legacy sweep did (replaying an expired key would misread the probe
+	// rejection as "never charged").
+	payKeyedCount, payKeyedCompleted, payKeyedUnverified, err := sweepKeyedStaleRows(ctx, "payments", keyedCutoff)
+	if err != nil {
+		return 0, err
+	}
+	tillKeyedCount, tillKeyedCompleted, tillKeyedUnverified, err := sweepKeyedStaleRows(ctx, "till_sales", keyedCutoff)
 	if err != nil {
 		return 0, err
 	}
 
-	// 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.
+	// Pass 2 (legacy 24h cutoff): rows WITH a square_payment_id are reconciled
+	// by payment id; rows with neither a payment id nor a stored key cannot be
+	// reconciled and are failed directly (WARN — the charge outcome is unknown).
+	payCount, payCompleted, err := sweepStaleRows(ctx, "payments", cutoff)
+	if err != nil {
+		return 0, err
+	}
 	tillCount, tillCompleted, err := sweepStaleRows(ctx, "till_sales", cutoff)
 	if err != nil {
 		return 0, err
 	}
 
-	total := payCount + tillCount
+	total := payKeyedCount + tillKeyedCount + payCount + tillCount
+	payTotal := payKeyedCount + payCount
+	tillTotal := tillKeyedCount + tillCount
+	completed := payKeyedCompleted + tillKeyedCompleted + payCompleted + tillCompleted
 	if total > 0 {
-		log.Printf("[SWEEP] Resolved %d stale pending payments (%d payments, %d till sales) older than %s — late retries will be rejected, preventing a second Square charge; %d reconciled to completed against Square (%d payments, %d till sales)", total, payCount, tillCount, stalePendingPaymentAge, payCompleted+tillCompleted, payCompleted, tillCompleted)
+		log.Printf("[SWEEP] Resolved %d stale pending payments (%d payments, %d till sales) older than %s — late retries will be rejected, preventing a second Square charge; %d reconciled to completed against Square (%d payments, %d till sales)", total, payTotal, tillTotal, stalePendingPaymentAge, completed, payKeyedCompleted+payCompleted, tillKeyedCompleted+tillCompleted)
 	}
 	// Routine sweep bookkeeping, not an incident: failing stale pending rows is
 	// the sweep's DESIGNED behaviour. A row swept to failed may still have been
 	// charged at Square with a lost response, so note it at WARN level for an
 	// admin doing a periodic money reconciliation — but this fires on every
 	// normal run and must not be elevated to CRITICAL (which is reserved for
-	// genuinely unrecoverable post-charge branches).
+	// genuinely unrecoverable post-charge branches). Rows the keyed reconcile
+	// PROVED never charged are deliberately excluded from the WARN (they cannot
+	// have moved money); only rows failed without a reconcile proof — keyless
+	// rows and keyed rows past the retention window — are counted.
+	if payKeyedUnverified > 0 {
+		log.Printf("[SWEEP] WARN: %d pending payments with a stored idempotency key but no square_payment_id were marked failed without a replay reconcile (key retention window already closed) — may have been charged at Square with a lost response — verify before refunding/charging", payKeyedUnverified)
+	}
+	if tillKeyedUnverified > 0 {
+		log.Printf("[SWEEP] WARN: %d pending till sales with a stored idempotency key but no square_payment_id were marked failed without a replay reconcile (key retention window already closed) — may have been charged at Square with a lost response", tillKeyedUnverified)
+	}
 	if payCount > 0 {
 		log.Printf("[SWEEP] WARN: %d pending payments marked failed may have been charged at Square with a lost response — verify before refunding/charging", payCount-payCompleted)
 	}
@@ -87,6 +135,18 @@ func SweepStalePendingPayments(ctx context.Context) (int, error) {
 type staleRow struct {
 	ID              string
 	SquarePaymentID string
+	// IdempotencyKey is the deterministic Square idempotency key stored on the
+	// pending row ("" when absent). Rows WITH a key but NO square_payment_id are
+	// the lost-response case: the sweep replays the key at Square to learn the
+	// true charge outcome before declaring failure.
+	IdempotencyKey string
+	// AmountPence is the row's charge amount in pence — the amount the original
+	// CreatePayment used. The replay-by-key must repeat it so Square's
+	// idempotency dedup returns the original payment.
+	AmountPence int64
+	// CreatedAt is the pending row's creation time; rows already past Square's
+	// idempotency-key retention window cannot be replayed trustworthily.
+	CreatedAt    time.Time
 	ItemID       string  // till_sales.item_id — the gift card ("" when NULL / non-gift-card)
 	RedeemToUserID  *string // gift_cards.redeemed_by — user credited by a create-with-redeem
 	IsCreate        bool    // true when this sale created the gift card (timestamps equal)
@@ -109,70 +169,15 @@ func sweepStaleRows(ctx context.Context, table string, cutoff time.Time) (resolv
 	default:
 		return 0, 0, fmt.Errorf("sweep: unknown stale table %q", table)
 	}
-	// The legacy till_sales sweep only touched card methods — cash and
-	// on_the_house are committed synchronously and never pending, but keep the
-	// predicate so behaviour is byte-identical for any unexpected row.
-	methodFilter := ""
-	if table == "till_sales" {
-		methodFilter = ` AND payment_method IN ('online_square', 'in_person_card')`
-	}
-	var rows pgx.Rows
-	if table == "till_sales" {
-		rows, err = db.Conn.Query(ctx, `
-			SELECT ts.id, COALESCE(ts.square_payment_id, ''), ts.item_id, gc.redeemed_by,
-			       (ts.created_at = gc.created_at) AS is_create,
-			       (gc.id IS NOT NULL) AS has_gift_card, ts.total_amount
-			FROM till_sales ts
-			LEFT JOIN gift_cards gc ON gc.id = ts.item_id
-			WHERE ts.status = 'pending' AND ts.created_at < $1`+methodFilter+`
-		`, cutoff)
-	} else {
-		rows, err = db.Conn.Query(ctx, `
-			SELECT id, COALESCE(square_payment_id, '')
-			FROM `+table+`
-			WHERE status = 'pending' AND created_at < $1`+methodFilter+`
-		`, cutoff)
-	}
+	stale, err := fetchStaleRows(ctx, table, cutoff, false)
 	if err != nil {
 		return 0, 0, err
 	}
-	var stale []staleRow
-	for rows.Next() {
-		var r staleRow
-		if table == "till_sales" {
-			var itemID, redeemedBy sql.NullString
-			var isCreate *bool
-			var hasGiftCard bool
-			if err := rows.Scan(&r.ID, &r.SquarePaymentID, &itemID, &redeemedBy, &isCreate, &hasGiftCard, &r.TotalAmount); err != nil {
-				log.Printf("Failed to scan stale pending row from %s: %v", table, err)
-				continue
-			}
-			r.ItemID = itemID.String
-			if redeemedBy.Valid && redeemedBy.String != "" {
-				r.RedeemToUserID = &redeemedBy.String
-			}
-			r.IsCreate = isCreate != nil && *isCreate
-			r.HasGiftCard = hasGiftCard
-		} else {
-			if err := rows.Scan(&r.ID, &r.SquarePaymentID); err != nil {
-				log.Printf("Failed to scan stale pending row from %s: %v", table, err)
-				continue
-			}
-		}
-		stale = append(stale, r)
-	}
-	rows.Close()
-
 	for _, r := range stale {
 		if r.SquarePaymentID != "" {
 			switch reconcileStalePaymentAtSquare(ctx, table, r.SquarePaymentID) {
 			case staleReconcileCompleted:
-				if tag, upErr := db.Conn.Exec(ctx, `
-					UPDATE `+table+` SET status = 'completed', updated_at = NOW()
-					WHERE id = $1 AND status = 'pending'
-				`, r.ID); upErr != nil {
-					log.Printf("Failed to rescue stale pending row %s to completed: %v", r.ID, upErr)
-				} else if n := int(tag.RowsAffected()); n > 0 {
+				if rescueStaleRowCompleted(ctx, table, r.ID) {
 					resolved++
 					completed++
 				}
@@ -194,6 +199,228 @@ func sweepStaleRows(ctx context.Context, table string, cutoff time.Time) (resolv
 		// (no square_payment_id — the charge outcome is unknown) NEVER claws
 		// back: the money may have landed at Square.
 		if table == "till_sales" && r.SquarePaymentID != "" && r.HasGiftCard {
+			if clawbackTillSaleFunding(ctx, r) {
+				resolved++
+			}
+			continue
+		}
+		if failStaleRow(ctx, table, r.ID) {
+			resolved++
+		}
+	}
+	return resolved, completed, nil
+}
+
+// sweepKeyedStaleRows resolves stale pending rows that carry a stored
+// idempotency key but no square_payment_id — the lost-response case, where the
+// charge may have completed at Square with the response never reaching the
+// app. Such rows are reconciled at Square by replaying the key while it is
+// still inside Square's ~24h retention window (the earlier stalePendingKeyedAge
+// cutoff guarantees this):
+//
+//   - a COMPLETED payment under the key → rescued to 'completed' with the real
+//     square_payment_id written back (the customer WAS charged);
+//   - a payment Square proves never happened (unknown key / FAILED status) →
+//     marked 'failed', and a till sale's funded gift card is clawed back
+//     (reconcile PROVED the funding has no charge behind it);
+//   - an ambiguous answer (transport/5xx) → left pending for the next run;
+//   - a row already older than the retention window when swept → cannot be
+//     replayed trustworthily (an expired key would misread the probe rejection
+//     as "never charged" even when the charge landed), so it is blind-failed
+//     with a WARN exactly as the legacy sweep did.
+//
+// Returns the total rows resolved, how many were rescued to 'completed', and
+// how many were marked failed WITHOUT a reconcile proof (blind-fail WARNs).
+func sweepKeyedStaleRows(ctx context.Context, table string, cutoff time.Time) (resolved, completed, unverifiable int, err error) {
+	switch table {
+	case "payments", "till_sales":
+	default:
+		return 0, 0, 0, fmt.Errorf("sweep: unknown stale table %q", table)
+	}
+	stale, err := fetchStaleRows(ctx, table, cutoff, true)
+	if err != nil {
+		return 0, 0, 0, err
+	}
+	// Square's idempotency-key retention window closes at stalePendingPaymentAge;
+	// a row older than that when swept can no longer be replayed trustworthily.
+	replayExpired := clock.Now().Add(-stalePendingPaymentAge)
+	for _, r := range stale {
+		if r.CreatedAt.Before(replayExpired) {
+			// Key retention window already closed — replaying would misread an
+			// expired key as "never charged". Blind-fail + WARN exactly as the
+			// legacy sweep did; a till sale's funded gift card is NOT clawed
+			// back (the charge outcome is unknown, the money may have landed).
+			if failStaleRow(ctx, table, r.ID) {
+				resolved++
+				unverifiable++
+			}
+			log.Printf("Stale pending %s row %s has a stored idempotency key but is already past Square's key retention window — marked failed without a replay reconcile (may have been charged with a lost response)", table, r.ID)
+			continue
+		}
+		switch res, sqPayID := reconcileStalePaymentByKey(ctx, table, r.IdempotencyKey, r.AmountPence); res {
+		case staleReconcileCompleted:
+			if rescueKeyedStaleRowCompleted(ctx, table, r.ID, sqPayID) {
+				resolved++
+				completed++
+			}
+		case staleReconcileLeavePending:
+			// Ambiguous replay — the charge may still be in flight. Leave the
+			// row pending; the next sweep run reconciles it again.
+			log.Printf("Stale pending %s row %s left pending (replay-by-key reconcile ambiguous) — will retry next sweep", table, r.ID)
+		case staleReconcileDefinitivelyFailed:
+			// Square proved the charge never happened (key unknown / FAILED) —
+			// a till sale's funded gift card is clawed back atomically with the
+			// failed mark, unlike the blind-fail path where the outcome is unknown.
+			if table == "till_sales" && r.HasGiftCard {
+				if clawbackTillSaleFunding(ctx, r) {
+					resolved++
+				}
+				continue
+			}
+			if failStaleRow(ctx, table, r.ID) {
+				resolved++
+			}
+		}
+	}
+	return resolved, completed, unverifiable, nil
+}
+
+// fetchStaleRows reads the stale pending rows of one table that are older than
+// cutoff. keyedOnly restricts the query to rows that can be reconciled by
+// replaying a stored idempotency key: those with a key but no square_payment_id
+// (rows WITH a square_payment_id are reconciled by payment id in the main
+// pass). The legacy till_sales sweep only touches card methods — cash and
+// on_the_house are committed synchronously and never pending, but the
+// predicate is kept so behaviour is byte-identical for any unexpected row.
+func fetchStaleRows(ctx context.Context, table string, cutoff time.Time, keyedOnly bool) ([]staleRow, error) {
+	keyedPredicate := ""
+	if keyedOnly {
+		keyedPredicate = ` AND idempotency_key IS NOT NULL AND square_payment_id IS NULL`
+	}
+	methodFilter := ""
+	if table == "till_sales" {
+		methodFilter = ` AND payment_method IN ('online_square', 'in_person_card')`
+	}
+	var rows pgx.Rows
+	var err error
+	if table == "till_sales" {
+		rows, err = db.Conn.Query(ctx, `
+			SELECT ts.id, COALESCE(ts.square_payment_id, ''), COALESCE(ts.idempotency_key, ''),
+			       ts.created_at, ts.item_id, gc.redeemed_by,
+			       (ts.created_at = gc.created_at) AS is_create,
+			       (gc.id IS NOT NULL) AS has_gift_card, ts.total_amount
+			FROM till_sales ts
+			LEFT JOIN gift_cards gc ON gc.id = ts.item_id
+			WHERE ts.status = 'pending' AND ts.created_at < $1`+methodFilter+keyedPredicate+`
+		`, cutoff)
+	} else {
+		rows, err = db.Conn.Query(ctx, `
+			SELECT id, COALESCE(square_payment_id, ''), COALESCE(idempotency_key, ''),
+			       created_at, amount
+			FROM `+table+`
+			WHERE status = 'pending' AND created_at < $1`+keyedPredicate+`
+		`, cutoff)
+	}
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	var stale []staleRow
+	for rows.Next() {
+		r, scanErr := scanStaleRow(table, rows)
+		if scanErr != nil {
+			log.Printf("Failed to scan stale pending row from %s: %v", table, scanErr)
+			continue
+		}
+		stale = append(stale, r)
+	}
+	return stale, rows.Err()
+}
+
+// scanStaleRow scans one row produced by fetchStaleRows into a staleRow,
+// deriving the replay amount (in pence) from the stored pound figure — the
+// original CreatePayment amount the replay-by-key must repeat.
+func scanStaleRow(table string, rows pgx.Rows) (staleRow, error) {
+	var r staleRow
+	if table == "till_sales" {
+		var itemID, redeemedBy sql.NullString
+		var isCreate *bool
+		var hasGiftCard bool
+		if err := rows.Scan(&r.ID, &r.SquarePaymentID, &r.IdempotencyKey, &r.CreatedAt,
+			&itemID, &redeemedBy, &isCreate, &hasGiftCard, &r.TotalAmount); err != nil {
+			return r, err
+		}
+		r.ItemID = itemID.String
+		if redeemedBy.Valid && redeemedBy.String != "" {
+			r.RedeemToUserID = &redeemedBy.String
+		}
+		r.IsCreate = isCreate != nil && *isCreate
+		r.HasGiftCard = hasGiftCard
+		r.AmountPence = int64(math.Round(r.TotalAmount * 100))
+		return r, nil
+	}
+	var amount float64
+	if err := rows.Scan(&r.ID, &r.SquarePaymentID, &r.IdempotencyKey, &r.CreatedAt, &amount); err != nil {
+		return r, err
+	}
+	r.AmountPence = int64(math.Round(amount * 100))
+	return r, nil
+}
+
+// failStaleRow marks one stale pending row 'failed'. Returns true when the row
+// was updated (status was still 'pending').
+func failStaleRow(ctx context.Context, table, id string) bool {
+	tag, err := db.Conn.Exec(ctx, `
+		UPDATE `+table+` SET status = 'failed', updated_at = NOW()
+		WHERE id = $1 AND status = 'pending'
+	`, id)
+	if err != nil {
+		log.Printf("Failed to mark stale pending row %s failed: %v", id, err)
+		return false
+	}
+	return int(tag.RowsAffected()) > 0
+}
+
+// rescueStaleRowCompleted marks one stale pending row (whose square_payment_id
+// already resolves to a COMPLETED charge) 'completed'. Returns true when the
+// row was updated.
+func rescueStaleRowCompleted(ctx context.Context, table, id string) bool {
+	tag, err := db.Conn.Exec(ctx, `
+		UPDATE `+table+` SET status = 'completed', updated_at = NOW()
+		WHERE id = $1 AND status = 'pending'
+	`, id)
+	if err != nil {
+		log.Printf("Failed to rescue stale pending row %s to completed: %v", id, err)
+		return false
+	}
+	return int(tag.RowsAffected()) > 0
+}
+
+// rescueKeyedStaleRowCompleted marks a keyed stale pending row 'completed' with
+// the square_payment_id returned by the replay — the lost-response rescue. The
+// reconcile is deliberately minimal (status + square_payment_id + updated_at
+// only, no split/VAT recomputation): the row is >22h stale and this is a
+// reconciliation rescue, mirroring the F3 by-id rescue's minimality. Returns
+// true when the row was updated.
+func rescueKeyedStaleRowCompleted(ctx context.Context, table, id, squarePaymentID string) bool {
+	tag, err := db.Conn.Exec(ctx, `
+		UPDATE `+table+` SET status = 'completed', square_payment_id = $1, updated_at = NOW()
+		WHERE id = $2 AND status = 'pending'
+	`, squarePaymentID, id)
+	if err != nil {
+		log.Printf("Failed to rescue stale pending row %s to completed: %v", id, err)
+		return false
+	}
+	return int(tag.RowsAffected()) > 0
+}
+
+// clawbackTillSaleFunding claws back a stale pending till sale's funded gift
+// card (atomically with the failed mark) after a reconcile PROVED the charge
+// never completed — the funding has no charge behind it. A sale with no gift
+// card is only marked failed. Returns true when the sale was resolved to
+// failed; false when it was already resolved by someone else, had no gift card,
+// or the clawback failed (CRITICAL logged).
+func clawbackTillSaleFunding(ctx context.Context, r staleRow) bool {
 	action := "topup"
 	if r.IsCreate {
 		action = "create"
@@ -201,24 +428,55 @@ func sweepStaleRows(ctx context.Context, table string, cutoff time.Time) (resolv
 	if revErr := revertGiftCardFunding(ctx, action, r.ItemID, r.TotalAmount, r.RedeemToUserID, r.ID); revErr != nil {
 		if errors.Is(revErr, errTillSaleNotPending) {
 			log.Printf("Stale pending till sale %s was already resolved (not pending) — skipping funding clawback", r.ID)
-					continue
+			return false
 		}
 		log.Printf("CRITICAL: failed to claw back gift card %s funding for stale till sale %s: %v — MANUAL RECONCILIATION REQUIRED: gift card may still be funded", r.ItemID, r.ID, revErr)
-				continue
+		return false
 	}
-			resolved++
-			continue
+	return true
 }
-		if tag, upErr := db.Conn.Exec(ctx, `
-			UPDATE `+table+` SET status = 'failed', updated_at = NOW()
-			WHERE id = $1 AND status = 'pending'
-		`, r.ID); upErr != nil {
-			log.Printf("Failed to mark stale pending row %s failed: %v", r.ID, upErr)
-		} else if n := int(tag.RowsAffected()); n > 0 {
-			resolved++
+
+// reconcileStalePaymentByKey asks Square for the authoritative status of the
+// charge made under a stale pending row's idempotency key and returns the
+// tri-state result. The replay returns the ORIGINAL payment for a retained key
+// (Square's documented idempotency behavior — never a second charge); a
+// COMPLETED payment rescues the row to 'completed' with its real payment id. A
+// definitive rejection (ErrReplayKeyNotRetained — Square has no payment under
+// the key, so the charge never happened) or a FAILED/CANCELED payment proves
+// the charge never completed and fails the row. Any OTHER error (transport /
+// 5xx / ambiguous) leaves the row pending — the charge may still have
+// completed at Square. The second return value is the Square payment id of the
+// completed payment ("" otherwise), written back on a rescue.
+func reconcileStalePaymentByKey(ctx context.Context, table, idempotencyKey string, amountPence int64) (staleReconcileResult, string) {
+	pr, err := SquareClient.ReplayPaymentByKey(ctx, idempotencyKey, amountPence)
+	if err != nil {
+		if errors.Is(err, square.ErrReplayKeyNotRetained) {
+			log.Printf("Stale pending %s reconcile by key: Square has no payment under the stored idempotency key (replay probe rejected) — marking failed; the charge provably never happened", table)
+			return staleReconcileDefinitivelyFailed, ""
 		}
+		log.Printf("Stale pending %s reconcile by idempotency key hit an ambiguous error (%v) — leaving pending for a later sweep run", table, err)
+		return staleReconcileLeavePending, ""
+	}
+	// Square's terminal payment states are COMPLETED, CANCELED, FAILED;
+	// APPROVED (authorization-only, delayed capture) and PENDING are
+	// NON-terminal — both can still transition to COMPLETED, so clawing back
+	// the funded gift card on either would risk reversing a charge that later
+	// lands. This app always creates payments with autocomplete (default true),
+	// so it never produces APPROVED/PENDING rows today, but the classification
+	// must match Square's documented state machine.
+	switch pr.Status {
+	case "COMPLETED":
+		return staleReconcileCompleted, pr.ID
+	case "CANCELED", "FAILED":
+		log.Printf("Stale pending %s is %q at Square (replay by key) — marking failed", table, pr.Status)
+		return staleReconcileDefinitivelyFailed, ""
+	case "APPROVED", "PENDING":
+		log.Printf("Stale pending %s is %q at Square (replay by key, non-terminal) — leaving pending for a later sweep run", table, pr.Status)
+		return staleReconcileLeavePending, ""
+	default:
+		log.Printf("Stale pending %s is %q at Square (replay by key) — marking failed", table, pr.Status)
+		return staleReconcileDefinitivelyFailed, ""
 	}
-	return resolved, completed, nil
 }
 
 // staleReconcileResult is the tri-state outcome of reconciling one stale

backend/handlers/payments/sweep_test.go

@@ -237,6 +237,363 @@ func (c *completedTerminalClient) GetCheckout(ctx context.Context, checkoutID st
 	return c.SquareClient.GetCheckout(ctx, checkoutID)
 }
 
+// =============================================================================
+// SweepStalePendingPayments — lost-response reconcile by idempotency key
+// =============================================================================
+
+// staleReplayClient forces ReplayPaymentByKey to return a fixed result/error so
+// the keyed-reconcile branches can be exercised deterministically.
+type staleReplayClient struct {
+	square.SquareClient
+	result *square.PaymentResult
+	err    error
+}
+
+func (c *staleReplayClient) ReplayPaymentByKey(ctx context.Context, idempotencyKey string, amount int64) (*square.PaymentResult, error) {
+	if c.err != nil {
+		return nil, c.err
+	}
+	if c.result != nil {
+		return c.result, nil
+	}
+	return c.SquareClient.ReplayPaymentByKey(ctx, idempotencyKey, amount)
+}
+
+// TestSweepStalePendingPayments_KeyedLostResponse_CompletedRescued locks the
+// lost-response gap: a pending payment with a stored idempotency key but no
+// square_payment_id whose charge actually COMPLETED at Square (the response
+// was lost) is rescued to 'completed' with the real square_payment_id written
+// back by replaying the key, instead of being blind-failed.
+func TestSweepStalePendingPayments_KeyedLostResponse_CompletedRescued(t *testing.T) {
+	ctx, tx := testutils.SetupTestTx(t)
+
+	userID, err := fixtures.CreateTestUser(tx)
+	if err != nil {
+		t.Fatalf("failed to create user: %v", err)
+	}
+	serviceID, err := fixtures.CreateTestService(tx)
+	if err != nil {
+		t.Fatalf("failed to create service: %v", err)
+	}
+	bookingID, err := fixtures.CreateTestBookingAtTime(tx, userID, serviceID,
+		time.Date(2099, 12, 31, 10, 0, 0, 0, time.UTC))
+	if err != nil {
+		t.Fatalf("failed to create booking: %v", err)
+	}
+
+	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)
+	}
+	// 23h old: past the 22h keyed cutoff (so the keyed pass picks it up) but
+	// still inside Square's 24h idempotency-key retention window (so the replay
+	// returns the original payment instead of being blind-failed).
+	const key = "key-lost-response-completed"
+	if _, err := tx.Exec(ctx, "UPDATE payments SET created_at = NOW() - INTERVAL '23 hours', idempotency_key = $1 WHERE id = $2", key, staleID); err != nil {
+		t.Fatalf("failed to age the stale payment: %v", err)
+	}
+
+	origClient := SquareClient
+	mock := square.NewDevClient().(*square.MockClient)
+	// Seed the completed charge at Square under the SAME idempotency key the
+	// pending row stores — the lost-response state the sweep must recover from.
+	pay, err := mock.CreatePayment(context.Background(), square.CreatePaymentReq{
+		Amount:         200000,
+		Currency:       "GBP",
+		SourceID:       "cnon:test-card",
+		IdempotencyKey: key,
+	})
+	if err != nil {
+		t.Fatalf("failed to seed completed Square payment: %v", err)
+	}
+	SquareClient = mock
+	defer func() { SquareClient = origClient }()
+
+	pgxTx := db.TxFromContext(ctx)
+	if pgxTx == nil {
+		t.Fatal("no transaction in context")
+	}
+	if err := pgxTx.Commit(ctx); err != nil {
+		t.Fatalf("failed to commit test tx: %v", err)
+	}
+
+	t.Cleanup(func() {
+		_, _ = db.Conn.Exec(context.Background(), `DELETE FROM payments WHERE id = $1`, staleID)
+		_, _ = db.Conn.Exec(context.Background(), `DELETE FROM bookings WHERE id = $1`, bookingID)
+		_, _ = db.Conn.Exec(context.Background(), `DELETE FROM services WHERE id = $1`, serviceID)
+		_, _ = db.Conn.Exec(context.Background(), `DELETE FROM users WHERE id = $1`, userID)
+	})
+
+	freshCtx := context.Background()
+	if _, err := SweepStalePendingPayments(freshCtx); err != nil {
+		t.Fatalf("sweep failed: %v", err)
+	}
+
+	var status, sqPayID string
+	if err := db.Conn.QueryRow(freshCtx, "SELECT status, COALESCE(square_payment_id, '') FROM payments WHERE id = $1", staleID).Scan(&status, &sqPayID); err != nil {
+		t.Fatalf("failed to query payment: %v", err)
+	}
+	if status != "completed" {
+		t.Errorf("expected lost-response payment with a completed Square charge rescued to 'completed', got %q", status)
+	}
+	if sqPayID != pay.SquarePayID {
+		t.Errorf("expected square_payment_id %s written back on the rescue, got %q", pay.SquarePayID, sqPayID)
+	}
+}
+
+// TestSweepStalePendingPayments_KeyedLostResponse_NoPayment_Failed locks the
+// mirror case: a pending payment with a stored idempotency key but no
+// square_payment_id whose charge Square proves NEVER happened (no payment under
+// the key) is marked failed — the keyed reconcile runs before the fail, so no
+// row with a key is ever failed without checking Square first.
+func TestSweepStalePendingPayments_KeyedLostResponse_NoPayment_Failed(t *testing.T) {
+	ctx, tx := testutils.SetupTestTx(t)
+
+	userID, err := fixtures.CreateTestUser(tx)
+	if err != nil {
+		t.Fatalf("failed to create user: %v", err)
+	}
+	serviceID, err := fixtures.CreateTestService(tx)
+	if err != nil {
+		t.Fatalf("failed to create service: %v", err)
+	}
+	bookingID, err := fixtures.CreateTestBookingAtTime(tx, userID, serviceID,
+		time.Date(2099, 12, 31, 10, 0, 0, 0, time.UTC))
+	if err != nil {
+		t.Fatalf("failed to create booking: %v", err)
+	}
+
+	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 '23 hours', idempotency_key = 'key-lost-response-never' WHERE id = $1", staleID); err != nil {
+		t.Fatalf("failed to age the stale payment: %v", err)
+	}
+
+	// A fresh mock has no payment under the key → ReplayPaymentByKey returns
+	// ErrReplayKeyNotRetained → the charge provably never happened → failed.
+	origClient := SquareClient
+	SquareClient = square.NewDevClient()
+	defer func() { SquareClient = origClient }()
+
+	pgxTx := db.TxFromContext(ctx)
+	if pgxTx == nil {
+		t.Fatal("no transaction in context")
+	}
+	if err := pgxTx.Commit(ctx); err != nil {
+		t.Fatalf("failed to commit test tx: %v", err)
+	}
+
+	t.Cleanup(func() {
+		_, _ = db.Conn.Exec(context.Background(), `DELETE FROM payments WHERE id = $1`, staleID)
+		_, _ = db.Conn.Exec(context.Background(), `DELETE FROM bookings WHERE id = $1`, bookingID)
+		_, _ = db.Conn.Exec(context.Background(), `DELETE FROM services WHERE id = $1`, serviceID)
+		_, _ = db.Conn.Exec(context.Background(), `DELETE FROM users WHERE id = $1`, userID)
+	})
+
+	freshCtx := context.Background()
+	if _, err := SweepStalePendingPayments(freshCtx); err != nil {
+		t.Fatalf("sweep failed: %v", err)
+	}
+
+	var status string
+	if err := db.Conn.QueryRow(freshCtx, "SELECT status FROM payments WHERE id = $1", staleID).Scan(&status); err != nil {
+		t.Fatalf("failed to query payment: %v", err)
+	}
+	if status != "failed" {
+		t.Errorf("expected keyed payment with no charge at Square marked 'failed', got %q", status)
+	}
+}
+
+// TestSweepStalePendingPayments_KeyedLostResponse_Ambiguous_LeavesPending locks
+// the conservative keyed-reconcile rule: an ambiguous replay (transport error)
+// leaves the keyed row pending — the charge may still be in flight at Square.
+func TestSweepStalePendingPayments_KeyedLostResponse_Ambiguous_LeavesPending(t *testing.T) {
+	ctx, tx := testutils.SetupTestTx(t)
+
+	userID, err := fixtures.CreateTestUser(tx)
+	if err != nil {
+		t.Fatalf("failed to create user: %v", err)
+	}
+	serviceID, err := fixtures.CreateTestService(tx)
+	if err != nil {
+		t.Fatalf("failed to create service: %v", err)
+	}
+	bookingID, err := fixtures.CreateTestBookingAtTime(tx, userID, serviceID,
+		time.Date(2099, 12, 31, 10, 0, 0, 0, time.UTC))
+	if err != nil {
+		t.Fatalf("failed to create booking: %v", err)
+	}
+
+	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 '23 hours', idempotency_key = 'key-lost-response-ambiguous' WHERE id = $1", staleID); err != nil {
+		t.Fatalf("failed to age the stale payment: %v", err)
+	}
+
+	origClient := SquareClient
+	SquareClient = &staleReplayClient{SquareClient: square.NewDevClient(), err: fmt.Errorf("network error: connection reset by peer")}
+	defer func() { SquareClient = origClient }()
+
+	pgxTx := db.TxFromContext(ctx)
+	if pgxTx == nil {
+		t.Fatal("no transaction in context")
+	}
+	if err := pgxTx.Commit(ctx); err != nil {
+		t.Fatalf("failed to commit test tx: %v", err)
+	}
+
+	t.Cleanup(func() {
+		_, _ = db.Conn.Exec(context.Background(), `DELETE FROM payments WHERE id = $1`, staleID)
+		_, _ = db.Conn.Exec(context.Background(), `DELETE FROM bookings WHERE id = $1`, bookingID)
+		_, _ = db.Conn.Exec(context.Background(), `DELETE FROM services WHERE id = $1`, serviceID)
+		_, _ = db.Conn.Exec(context.Background(), `DELETE FROM users WHERE id = $1`, userID)
+	})
+
+	freshCtx := context.Background()
+	if _, err := SweepStalePendingPayments(freshCtx); err != nil {
+		t.Fatalf("sweep failed: %v", err)
+	}
+
+	var status string
+	if err := db.Conn.QueryRow(freshCtx, "SELECT status FROM payments WHERE id = $1", staleID).Scan(&status); err != nil {
+		t.Fatalf("failed to query payment: %v", err)
+	}
+	if status != "pending" {
+		t.Errorf("expected ambiguous keyed replay to leave the payment pending, got %q", status)
+	}
+}
+
+// TestSweepStalePendingPayments_KeyedTillLostResponse_CompletedRescued locks the
+// keyed lost-response rescue for till_sales: a stale pending till sale with a
+// stored idempotency key but no square_payment_id whose charge completed at
+// Square is rescued to 'completed' with the square_payment_id written back.
+func TestSweepStalePendingPayments_KeyedTillLostResponse_CompletedRescued(t *testing.T) {
+	ctx, tx := testutils.SetupTestTx(t)
+
+	adminID, err := fixtures.CreateTestAdminUser(tx)
+	if err != nil {
+		t.Fatalf("failed to create admin user: %v", err)
+	}
+
+	origClient := SquareClient
+	mock := square.NewDevClient().(*square.MockClient)
+	pay, err := mock.CreatePayment(context.Background(), square.CreatePaymentReq{
+		Amount:         5000,
+		Currency:       "GBP",
+		SourceID:       "cnon:test-card",
+		IdempotencyKey: "key-lost-till-completed",
+	})
+	if err != nil {
+		t.Fatalf("failed to seed completed Square payment: %v", err)
+	}
+	SquareClient = mock
+	defer func() { SquareClient = origClient }()
+
+	var saleID string
+	err = tx.QueryRow(ctx, `
+		INSERT INTO till_sales (item_type, description, quantity, unit_price, total_amount, payment_method, status, idempotency_key, created_by, created_at, updated_at)
+		VALUES ('gift_card', 'Gift Card create', 1, 50.00, 50.00, 'online_square', 'pending', $1, $2, NOW() - INTERVAL '23 hours', NOW())
+		RETURNING id
+	`, "key-lost-till-completed", adminID).Scan(&saleID)
+	if err != nil {
+		t.Fatalf("failed to seed stale pending till sale: %v", err)
+	}
+
+	pgxTx := db.TxFromContext(ctx)
+	if pgxTx == nil {
+		t.Fatal("no transaction in context")
+	}
+	if err := pgxTx.Commit(ctx); err != nil {
+		t.Fatalf("failed to commit test tx: %v", err)
+	}
+
+	t.Cleanup(func() {
+		_, _ = db.Conn.Exec(context.Background(), `DELETE FROM till_sales WHERE id = $1`, saleID)
+		_, _ = db.Conn.Exec(context.Background(), `DELETE FROM users WHERE id = $1`, adminID)
+	})
+
+	freshCtx := context.Background()
+	if _, err := SweepStalePendingPayments(freshCtx); err != nil {
+		t.Fatalf("sweep failed: %v", err)
+	}
+
+	var status, sqPayID string
+	if err := db.Conn.QueryRow(freshCtx, "SELECT status, COALESCE(square_payment_id, '') FROM till_sales WHERE id = $1", saleID).Scan(&status, &sqPayID); err != nil {
+		t.Fatalf("failed to query till sale: %v", err)
+	}
+	if status != "completed" {
+		t.Errorf("expected lost-response till sale with a completed Square charge rescued to 'completed', got %q", status)
+	}
+	if sqPayID != pay.SquarePayID {
+		t.Errorf("expected square_payment_id %s written back on the till sale rescue, got %q", pay.SquarePayID, sqPayID)
+	}
+}
+
+// TestSweepStalePendingPayments_KeyedTillLostResponse_ProvenFailed_Clawbacks
+// locks the keyed clawback: a stale pending till sale with a stored idempotency
+// key whose charge Square PROVES never happened (no payment under the key) is
+// marked failed AND its funded gift card is clawed back — unlike the blind-fail
+// path, the reconcile proved the funding has no charge behind it.
+func TestSweepStalePendingPayments_KeyedTillLostResponse_ProvenFailed_Clawbacks(t *testing.T) {
+	ctx, tx := testutils.SetupTestTx(t)
+
+	adminID, err := fixtures.CreateTestAdminUser(tx)
+	if err != nil {
+		t.Fatalf("failed to create admin user: %v", err)
+	}
+	pool := context.Background()
+
+	saleID, giftCardID := seedStaleTillSaleWithCard(t, ctx, tx, adminID, 50.00, "", true)
+	// Move both the sale and its created gift card inside the key window (23h,
+	// created_at equality preserved → is_create stays true) and add the key.
+	if _, err := tx.Exec(ctx, "UPDATE till_sales SET created_at = NOW() - INTERVAL '23 hours', idempotency_key = 'key-lost-till-never' WHERE id = $1", saleID); err != nil {
+		t.Fatalf("failed to age the till sale: %v", err)
+	}
+	if _, err := tx.Exec(ctx, "UPDATE gift_cards SET created_at = NOW() - INTERVAL '23 hours' WHERE id = $1", giftCardID); err != nil {
+		t.Fatalf("failed to age the gift card: %v", err)
+	}
+
+	// A fresh mock has no payment under the key → ReplayPaymentByKey returns
+	// ErrReplayKeyNotRetained → definitively failed → clawback.
+	origClient := SquareClient
+	SquareClient = square.NewDevClient()
+	defer func() { SquareClient = origClient }()
+
+	pgxTx := db.TxFromContext(ctx)
+	if pgxTx == nil {
+		t.Fatal("no transaction in context")
+	}
+	if err := pgxTx.Commit(ctx); err != nil {
+		t.Fatalf("failed to commit setup tx: %v", err)
+	}
+
+	if _, err := SweepStalePendingPayments(pool); err != nil {
+		t.Fatalf("sweep failed: %v", err)
+	}
+
+	var status string
+	if err := db.Conn.QueryRow(pool, `SELECT status FROM till_sales WHERE id = $1`, saleID).Scan(&status); err != nil {
+		t.Fatalf("failed to query till sale: %v", err)
+	}
+	if status != "failed" {
+		t.Errorf("expected keyed till sale with no charge at Square marked failed, got %q", status)
+	}
+
+	// The reconcile PROVED the charge never happened, so the created gift card
+	// must have been clawed back (deleted).
+	var cardCount int
+	if err := db.Conn.QueryRow(pool, `SELECT COUNT(*) FROM gift_cards WHERE id = $1`, giftCardID).Scan(&cardCount); err != nil {
+		t.Fatalf("failed to count gift cards: %v", err)
+	}
+	if cardCount != 0 {
+		t.Errorf("expected the clawed-back created gift card deleted after keyed proof, got %d cards", cardCount)
+	}
+}
+
 // TestSweepStaleTerminalCheckouts_CancelsStalePending locks the F4 fix: a
 // terminal checkout still PENDING at Square after an hour is cancelled and its
 // till_sales row moved to the terminal 'failed' state (the payment_status enum
@@ -1065,3 +1422,262 @@ func TestSweepStaleTerminalCheckouts_TillCancelRequested_NoClawback(t *testing.T
 		t.Errorf("expected card untouched after CANCEL_REQUESTED-only, got count=%d remaining=%.2f", cardCount, remaining)
 	}
 }
+
+// =============================================================================
+// SweepStaleTerminalCheckouts — intermediate states via the dev mock's
+// ForceCheckoutState (mirrors the real Square API, not a fake client)
+// =============================================================================
+
+// TestSweepStaleTerminalCheckouts_MockCanceled_Clawbacks exercises the
+// isCheckoutDefinitivelyDead CANCELED direction through the DEV MOCK's own
+// forced state: a CANCELED checkout is provably dead, so the stale till-sale
+// is failed AND its funded gift card is clawed back. Before ForceCheckoutState
+// the mock could only auto-complete or stay PENDING, so this sweep branch was
+// only reachable via a fake client.
+func TestSweepStaleTerminalCheckouts_MockCanceled_Clawbacks(t *testing.T) {
+	ctx, tx := testutils.SetupTestTx(t)
+
+	adminID, err := fixtures.CreateTestAdminUser(tx)
+	if err != nil {
+		t.Fatalf("failed to create admin user: %v", err)
+	}
+	pool := context.Background()
+
+	// Force the checkout into the terminal CANCELED state — the mock's
+	// GetCheckout then emits the same plain "is CANCELED (not COMPLETED)"
+	// error the real client surfaces, which the sweep classifies as dead.
+	mock := square.NewDevClient().(*square.MockClient)
+	mock.ForceCheckoutState = "CANCELED"
+	checkout, err := mock.CreateCheckout(context.Background(), square.CreateCheckoutReq{
+		Amount:         5000,
+		Currency:       "GBP",
+		IdempotencyKey: "chk-mock-canceled",
+	})
+	if err != nil {
+		t.Fatalf("failed to create forced-CANCELED checkout: %v", err)
+	}
+	if checkout.Status != "CANCELED" {
+		t.Fatalf("expected forced CANCELED checkout, got %q", checkout.Status)
+	}
+
+	saleID, giftCardID := seedStaleTerminalTillSale(t, ctx, tx, adminID, true)
+	if _, err := tx.Exec(ctx, `UPDATE till_sales SET square_checkout_id = $1 WHERE id = $2`, checkout.ID, saleID); err != nil {
+		t.Fatalf("failed to set checkout id: %v", err)
+	}
+	if _, err := tx.Exec(ctx, `
+		INSERT INTO gift_card_transactions (gift_card_id, transaction_type, amount, reference_type, reference_id)
+		VALUES ($1, 'purchase', 50.00, 'till_sale', $2)
+	`, giftCardID, saleID); err != nil {
+		t.Fatalf("failed to seed gift card transaction: %v", err)
+	}
+
+	origClient := SquareClient
+	SquareClient = mock
+	defer func() { SquareClient = origClient }()
+
+	pgxTx := db.TxFromContext(ctx)
+	if pgxTx == nil {
+		t.Fatal("no transaction in context")
+	}
+	if err := pgxTx.Commit(ctx); err != nil {
+		t.Fatalf("failed to commit setup tx: %v", err)
+	}
+
+	// Drop any other stale terminal rows left by parallel tests so the count is
+	// deterministic.
+	if _, err := db.Conn.Exec(pool, `DELETE FROM till_sales WHERE status = 'pending' AND square_checkout_id IS NOT NULL AND id <> $1`, saleID); err != nil {
+		t.Fatalf("failed to clean leftover stale terminal sales: %v", err)
+	}
+	if _, err := db.Conn.Exec(pool, `DELETE FROM terminal_checkouts WHERE status IN ('PENDING', 'IN_PROGRESS')`); err != nil {
+		t.Fatalf("failed to clean leftover stale booking terminal checkouts: %v", err)
+	}
+
+	n, err := SweepStaleTerminalCheckouts(pool)
+	if err != nil {
+		t.Fatalf("sweep failed: %v", err)
+	}
+	if n != 1 {
+		t.Errorf("expected exactly 1 resolved stale terminal checkout, got %d", n)
+	}
+
+	var status string
+	if err := db.Conn.QueryRow(pool, `SELECT status FROM till_sales WHERE id = $1`, saleID).Scan(&status); err != nil {
+		t.Fatalf("failed to query till sale: %v", err)
+	}
+	if status != "failed" {
+		t.Errorf("expected definitively-cancelled till sale marked failed, got %q", status)
+	}
+
+	// The created gift card must have been clawed back (deleted).
+	var cardCount int
+	if err := db.Conn.QueryRow(pool, `SELECT COUNT(*) FROM gift_cards WHERE id = $1`, giftCardID).Scan(&cardCount); err != nil {
+		t.Fatalf("failed to count gift cards: %v", err)
+	}
+	if cardCount != 0 {
+		t.Errorf("expected the clawed-back created gift card deleted, got %d cards", cardCount)
+	}
+}
+
+// TestSweepStaleTerminalCheckouts_MockNotFound_Clawbacks exercises the
+// isCheckoutDefinitivelyDead NOT_FOUND direction through the dev mock: a
+// square_checkout_id that references a checkout Square has never seen (expired
+// checkout, e.g.) resolves to the mock's plain "checkout not found" error,
+// which the sweep classifies as definitively dead and claws back.
+func TestSweepStaleTerminalCheckouts_MockNotFound_Clawbacks(t *testing.T) {
+	ctx, tx := testutils.SetupTestTx(t)
+
+	adminID, err := fixtures.CreateTestAdminUser(tx)
+	if err != nil {
+		t.Fatalf("failed to create admin user: %v", err)
+	}
+	pool := context.Background()
+
+	const checkoutID = "chk_never_created_mock"
+	saleID, giftCardID := seedStaleTerminalTillSale(t, ctx, tx, adminID, true)
+	if _, err := tx.Exec(ctx, `UPDATE till_sales SET square_checkout_id = $1 WHERE id = $2`, checkoutID, saleID); err != nil {
+		t.Fatalf("failed to set checkout id: %v", err)
+	}
+	if _, err := tx.Exec(ctx, `
+		INSERT INTO gift_card_transactions (gift_card_id, transaction_type, amount, reference_type, reference_id)
+		VALUES ($1, 'purchase', 50.00, 'till_sale', $2)
+	`, giftCardID, saleID); err != nil {
+		t.Fatalf("failed to seed gift card transaction: %v", err)
+	}
+
+	// A fresh mock holds no checkout under checkoutID → GetCheckout returns
+	// "checkout not found", which isTerminalCheckoutError / isCheckoutDefinitivelyDead
+	// classify as terminal + definitively dead.
+	origClient := SquareClient
+	SquareClient = square.NewDevClient()
+	defer func() { SquareClient = origClient }()
+
+	pgxTx := db.TxFromContext(ctx)
+	if pgxTx == nil {
+		t.Fatal("no transaction in context")
+	}
+	if err := pgxTx.Commit(ctx); err != nil {
+		t.Fatalf("failed to commit setup tx: %v", err)
+	}
+
+	if _, err := db.Conn.Exec(pool, `DELETE FROM till_sales WHERE status = 'pending' AND square_checkout_id IS NOT NULL AND id <> $1`, saleID); err != nil {
+		t.Fatalf("failed to clean leftover stale terminal sales: %v", err)
+	}
+	if _, err := db.Conn.Exec(pool, `DELETE FROM terminal_checkouts WHERE status IN ('PENDING', 'IN_PROGRESS')`); err != nil {
+		t.Fatalf("failed to clean leftover stale booking terminal checkouts: %v", err)
+	}
+
+	n, err := SweepStaleTerminalCheckouts(pool)
+	if err != nil {
+		t.Fatalf("sweep failed: %v", err)
+	}
+	if n != 1 {
+		t.Errorf("expected exactly 1 resolved stale terminal checkout, got %d", n)
+	}
+
+	var status string
+	if err := db.Conn.QueryRow(pool, `SELECT status FROM till_sales WHERE id = $1`, saleID).Scan(&status); err != nil {
+		t.Fatalf("failed to query till sale: %v", err)
+	}
+	if status != "failed" {
+		t.Errorf("expected not-found till sale marked failed, got %q", status)
+	}
+
+	var cardCount int
+	if err := db.Conn.QueryRow(pool, `SELECT COUNT(*) FROM gift_cards WHERE id = $1`, giftCardID).Scan(&cardCount); err != nil {
+		t.Fatalf("failed to count gift cards: %v", err)
+	}
+	if cardCount != 0 {
+		t.Errorf("expected the clawed-back created gift card deleted, got %d cards", cardCount)
+	}
+}
+
+// TestSweepStaleTerminalCheckouts_MockCancelRequested_CancelThenClawback
+// exercises the cancel-then-recheck path for a CANCEL_REQUESTED checkout via
+// the dev mock: GetCheckout folds CANCEL_REQUESTED into ErrCheckoutPending
+// (mirroring the real client, which treats it as still-live), the sweep calls
+// CancelCheckout (a no-op — Square returns 404 for an already-canceling
+// checkout), and the re-check — still ErrCheckoutPending — resolves the sale
+// to failed with the funding clawed back. The separate
+// CANCEL_REQUESTED-only "not provably dead, no clawback" classification of
+// isCheckoutDefinitivelyDead is locked by
+// TestSweepStaleTerminalCheckouts_TillCancelRequested_NoClawback, which
+// injects a non-pending CANCEL_REQUESTED error the real client never emits.
+func TestSweepStaleTerminalCheckouts_MockCancelRequested_CancelThenClawback(t *testing.T) {
+	ctx, tx := testutils.SetupTestTx(t)
+
+	adminID, err := fixtures.CreateTestAdminUser(tx)
+	if err != nil {
+		t.Fatalf("failed to create admin user: %v", err)
+	}
+	pool := context.Background()
+
+	mock := square.NewDevClient().(*square.MockClient)
+	mock.ForceCheckoutState = "CANCEL_REQUESTED"
+	checkout, err := mock.CreateCheckout(context.Background(), square.CreateCheckoutReq{
+		Amount:         5000,
+		Currency:       "GBP",
+		IdempotencyKey: "chk-mock-cancel-requested",
+	})
+	if err != nil {
+		t.Fatalf("failed to create forced-CANCEL_REQUESTED checkout: %v", err)
+	}
+	if checkout.Status != "CANCEL_REQUESTED" {
+		t.Fatalf("expected forced CANCEL_REQUESTED checkout, got %q", checkout.Status)
+	}
+
+	saleID, giftCardID := seedStaleTerminalTillSale(t, ctx, tx, adminID, true)
+	if _, err := tx.Exec(ctx, `UPDATE till_sales SET square_checkout_id = $1 WHERE id = $2`, checkout.ID, saleID); err != nil {
+		t.Fatalf("failed to set checkout id: %v", err)
+	}
+	if _, err := tx.Exec(ctx, `
+		INSERT INTO gift_card_transactions (gift_card_id, transaction_type, amount, reference_type, reference_id)
+		VALUES ($1, 'purchase', 50.00, 'till_sale', $2)
+	`, giftCardID, saleID); err != nil {
+		t.Fatalf("failed to seed gift card transaction: %v", err)
+	}
+
+	origClient := SquareClient
+	SquareClient = mock
+	defer func() { SquareClient = origClient }()
+
+	pgxTx := db.TxFromContext(ctx)
+	if pgxTx == nil {
+		t.Fatal("no transaction in context")
+	}
+	if err := pgxTx.Commit(ctx); err != nil {
+		t.Fatalf("failed to commit setup tx: %v", err)
+	}
+
+	if _, err := db.Conn.Exec(pool, `DELETE FROM till_sales WHERE status = 'pending' AND square_checkout_id IS NOT NULL AND id <> $1`, saleID); err != nil {
+		t.Fatalf("failed to clean leftover stale terminal sales: %v", err)
+	}
+	if _, err := db.Conn.Exec(pool, `DELETE FROM terminal_checkouts WHERE status IN ('PENDING', 'IN_PROGRESS')`); err != nil {
+		t.Fatalf("failed to clean leftover stale booking terminal checkouts: %v", err)
+	}
+
+	n, err := SweepStaleTerminalCheckouts(pool)
+	if err != nil {
+		t.Fatalf("sweep failed: %v", err)
+	}
+	if n != 1 {
+		t.Errorf("expected exactly 1 resolved stale terminal checkout, got %d", n)
+	}
+
+	var status string
+	if err := db.Conn.QueryRow(pool, `SELECT status FROM till_sales WHERE id = $1`, saleID).Scan(&status); err != nil {
+		t.Fatalf("failed to query till sale: %v", err)
+	}
+	if status != "failed" {
+		t.Errorf("expected CANCEL_REQUESTED (cancel-recheck) till sale marked failed, got %q", status)
+	}
+
+	// The sweep believed the cancel landed, so the created gift card is clawed
+	// back (deleted) — the same path the real Square API produces.
+	var cardCount int
+	if err := db.Conn.QueryRow(pool, `SELECT COUNT(*) FROM gift_cards WHERE id = $1`, giftCardID).Scan(&cardCount); err != nil {
+		t.Fatalf("failed to count gift cards: %v", err)
+	}
+	if cardCount != 0 {
+		t.Errorf("expected the clawed-back created gift card deleted, got %d cards", cardCount)
+	}
+}