fix(marketplace): escrow-required guard, ask-seller on active, scoped receipts

Correctness batch from MARKETPLACE_FLOW_AUDIT.md:
- canBuy is disabled when the seller requires escrow (item.escrow ===
  'required'), so a direct Buy-with-sats cannot bypass it.
- ask-seller (31872) is available on an active listing, not only once sold,
  so a buyer who paid off-app is no longer at a dead end.
- payment receipts (lib/receipts.ts) are scoped to the payer's pubkey, so a
  stale or foreign receipt cannot be attached to a trade by another account
  viewing the same listing.

MARKETPLACE_FLOW_AUDIT.md

@@ -218,6 +218,10 @@ Second batch (payment, attestation, escrow):
     documented in NIP.md; the buyer's escrow dialog includes that mint in the
     picker and prefers it, so the buyer locks at a mint the seller can redeem
     from. (Still open: seller-side receive from a mint they do not already have.)
+13. **Correctness guards:** fixed-price Buy is disabled when the seller requires
+    escrow (`item.escrow === 'required'`); ask-seller is available on an active
+    listing (not only once sold); payment receipts are scoped to the payer's
+    pubkey, so a stale/foreign receipt cannot be attached by another account.
 
 ## 7. Recommended order
 

src/components/ListingOffersPanel.tsx

@@ -338,7 +338,7 @@ export function ListingOffersPanel({ item, isOwner }: { item: MarketplaceItem; i
                 currency={payFor.latest.currency}
             onPaid={(receipt) => {
               // Carry the verifiable receipt to the confirm step (same coord key).
-              if (receipt) saveReceipt(payFor.listingCoord, receipt);
+              if (receipt) saveReceipt(payFor.listingCoord, receipt, 'payment', user?.pubkey ?? '');
               setPaidThreads((prev) => new Set(prev).add(`${payFor.listingCoord}:${payFor.buyer}`));
             }}
           />

src/components/ListingTradeActions.tsx

@@ -94,6 +94,8 @@ export function ListingTradeActions({ item }: { item: MarketplaceItem }) {
     !isSold &&
     !isExpired &&
     !iConfirmedTrade &&
+    // A seller who requires escrow must not be paid directly.
+    item.escrow !== 'required' &&
     item.priceType === 'fixed' &&
     typeof buyAmountSats === 'number' &&
     buyAmountSats > 0;
@@ -134,12 +136,12 @@ export function ListingTradeActions({ item }: { item: MarketplaceItem }) {
     // Attach the Lightning receipts captured at Pay time, if any — this is what
     // makes the trade payment-VERIFIED (sha256(preimage) === payment_hash), and
     // gives a barter a verifiable DEPOSIT cost.
-    const receipt = getReceipt(coord);
+    const receipt = getReceipt(coord, 'payment', user?.pubkey ?? '');
     const paymentProof =
       receipt?.preimage && receipt.paymentHash
         ? { preimage: receipt.preimage, paymentHash: receipt.paymentHash }
         : undefined;
-    const depositReceipt = getReceipt(coord, 'deposit');
+    const depositReceipt = getReceipt(coord, 'deposit', user?.pubkey ?? '');
     const depositProof =
       depositReceipt?.preimage && depositReceipt.paymentHash
         ? { preimage: depositReceipt.preimage, paymentHash: depositReceipt.paymentHash }
@@ -154,8 +156,8 @@ export function ListingTradeActions({ item }: { item: MarketplaceItem }) {
         paymentProof,
         depositProof,
       });
-      clearReceipt(coord);
-      clearReceipt(coord, 'deposit');
+      clearReceipt(coord, 'payment', user?.pubkey ?? '');
+      clearReceipt(coord, 'deposit', user?.pubkey ?? '');
       toast({
         title: t('marketUi.tradeActions.tradeConfirmed'),
         description:
@@ -251,7 +253,7 @@ export function ListingTradeActions({ item }: { item: MarketplaceItem }) {
       )}
 
       {/* Buyer: ask the seller to record the sale (kind 31872 request) */}
-      {!canEscrow && user && !isOwnListing && isSold && !iConfirmedTrade && !sellerNamedMe && !iRequestedConfirmation && (
+      {!canEscrow && user && !isOwnListing && !iConfirmedTrade && !sellerNamedMe && !iRequestedConfirmation && (
         <Button
           size="sm"
           variant="outline"
@@ -350,7 +352,7 @@ export function ListingTradeActions({ item }: { item: MarketplaceItem }) {
           sellerPubkey={item.pubkey}
           amountSats={Number(depositAmount) > 0 ? Number(depositAmount) : undefined}
           onPaid={(receipt) => {
-            if (receipt) saveReceipt(coord, receipt, 'deposit');
+            if (receipt) saveReceipt(coord, receipt, 'deposit', user?.pubkey ?? '');
             toast({
               title: t('marketUi.tradeActions.depositPaid'),
               description: t('marketUi.tradeActions.depositPaidBody'),
@@ -373,7 +375,7 @@ export function ListingTradeActions({ item }: { item: MarketplaceItem }) {
           amountSats={buyAmountSats ?? undefined}
           onPaid={(receipt) => {
             if (receipt) {
-              saveReceipt(`${MARKETPLACE_ITEM_KIND}:${item.pubkey}:${item.identifier}`, receipt);
+              saveReceipt(`${MARKETPLACE_ITEM_KIND}:${item.pubkey}:${item.identifier}`, receipt, 'payment', user?.pubkey ?? '');
             }
             toast({
               title: t('marketUi.tradeActions.paid'),

src/lib/receipts.ts

@@ -66,10 +66,6 @@ const STORAGE_KEY = 'skatespots:payment-receipts-v1';
 /** A trade can carry two receipts: the payment and (for barter) a deposit. */
 export type ReceiptSlot = 'payment' | 'deposit';
 
-function keyFor(coord: string, slot: ReceiptSlot): string {
-  return slot === 'deposit' ? `${coord}#deposit` : coord;
-}
-
 function loadAll(): Record<string, PaymentReceipt> {
   try {
     return JSON.parse(localStorage.getItem(STORAGE_KEY) ?? '{}') as Record<string, PaymentReceipt>;
@@ -78,24 +74,31 @@ function loadAll(): Record<string, PaymentReceipt> {
   }
 }
 
-export function saveReceipt(coord: string, receipt: PaymentReceipt, slot: ReceiptSlot = 'payment'): void {
+function keyFor(coord: string, slot: ReceiptSlot, owner: string): string {
+  const base = slot === 'deposit' ? `${coord}#deposit` : coord;
+  // Scope to the payer: a receipt must never be attached to a trade by a
+  // different account that happens to view the same listing.
+  return owner ? `${owner}|${base}` : base;
+}
+
+export function saveReceipt(coord: string, receipt: PaymentReceipt, slot: ReceiptSlot = 'payment', owner = ''): void {
   try {
     const all = loadAll();
-    all[keyFor(coord, slot)] = receipt;
+    all[keyFor(coord, slot, owner)] = receipt;
     localStorage.setItem(STORAGE_KEY, JSON.stringify(all));
   } catch {
     /* storage unavailable — the receipt just isn't carried forward */
   }
 }
 
-export function getReceipt(coord: string, slot: ReceiptSlot = 'payment'): PaymentReceipt | undefined {
-  return loadAll()[keyFor(coord, slot)];
+export function getReceipt(coord: string, slot: ReceiptSlot = 'payment', owner = ''): PaymentReceipt | undefined {
+  return loadAll()[keyFor(coord, slot, owner)];
 }
 
-export function clearReceipt(coord: string, slot: ReceiptSlot = 'payment'): void {
+export function clearReceipt(coord: string, slot: ReceiptSlot = 'payment', owner = ''): void {
   try {
     const all = loadAll();
-    delete all[keyFor(coord, slot)];
+    delete all[keyFor(coord, slot, owner)];
     localStorage.setItem(STORAGE_KEY, JSON.stringify(all));
   } catch {
     /* ignore */