diff --git a/client/src/tablet/Sale.tsx b/client/src/tablet/Sale.tsx
index 9177c14..d7ec122 100644
--- a/client/src/tablet/Sale.tsx
+++ b/client/src/tablet/Sale.tsx
@@ -22,6 +22,17 @@ export function Sale({ config, onChangeBar }: Props) {
   const longPressTimer = useRef<number | null>(null);
   const longPressFired = useRef(false);
 
+  // One idempotency key per pending cart, reused across retries of the same
+  // logical submission (e.g. after a timeout/dropped-connection error) so
+  // the server's client_uuid dedup can actually recognise a resend. Reset
+  // whenever the cart is cleared (submitted successfully or cancelled), so
+  // the *next* cart gets its own fresh id.
+  const cartUuidRef = useRef<string | null>(null);
+  function cartUuid() {
+    if (!cartUuidRef.current) cartUuidRef.current = uuid();
+    return cartUuidRef.current;
+  }
+
   const drinkById = useMemo(() => {
     const m = new Map<number, Drink>();
     drinks.forEach(d => m.set(d.id, d));
@@ -72,6 +83,7 @@ export function Sale({ config, onChangeBar }: Props) {
   function clear() {
     setLines([]);
     setPfandReturns(0);
+    cartUuidRef.current = null;
   }
 
   function startLongPress(d: Drink) {
@@ -115,7 +127,7 @@ export function Sale({ config, onChangeBar }: Props) {
     const items: CartItem[] = lines.map(l => ({ drink_id: l.drink_id, qty: l.qty }));
     try {
       await api.createTransaction({
-        client_uuid: uuid(),
+        client_uuid: cartUuid(),
         bar_id: bar.id,
         crew,
         items,
diff --git a/server/src/routes/public.ts b/server/src/routes/public.ts
index d607017..96a4e53 100644
--- a/server/src/routes/public.ts
+++ b/server/src/routes/public.ts
@@ -55,9 +55,12 @@ export function registerPublicRoutes(app: FastifyInstance, db: DB) {
       return reply.code(400).send({ error: 'empty transaction' });
     }
 
-    const existing = db
-      .prepare('SELECT id, total_cents FROM transactions WHERE client_uuid = ?')
-      .get(client_uuid) as { id: number; total_cents: number } | undefined;
+    const findByUuid = () =>
+      db
+        .prepare('SELECT id, total_cents FROM transactions WHERE client_uuid = ?')
+        .get(client_uuid) as { id: number; total_cents: number } | undefined;
+
+    const existing = findByUuid();
     if (existing) {
       const res: CreateTransactionResponse = { id: existing.id, total_cents: existing.total_cents };
       return res;
@@ -118,14 +121,31 @@ export function registerPublicRoutes(app: FastifyInstance, db: DB) {
     );
 
     const createdAt = new Date().toISOString();
-    const txId = db.transaction(() => {
-      const info = insertTx.run(bar_id, createdAt, paidTotal, crew ? 1 : 0, pfand_returns, clientIp, client_uuid);
-      const id = Number(info.lastInsertRowid);
-      for (const p of priced) {
-        insertItem.run(id, p.drink_id, p.qty, p.unit_price_cents, p.pfand_cents_per_unit);
+    let txId: number;
+    try {
+      txId = db.transaction(() => {
+        const info = insertTx.run(bar_id, createdAt, paidTotal, crew ? 1 : 0, pfand_returns, clientIp, client_uuid);
+        const id = Number(info.lastInsertRowid);
+        for (const p of priced) {
+          insertItem.run(id, p.drink_id, p.qty, p.unit_price_cents, p.pfand_cents_per_unit);
+        }
+        return id;
+      })();
+    } catch (e) {
+      // A UNIQUE violation on client_uuid means a concurrent/near-simultaneous
+      // retry of this exact submission won the race between our dedup check
+      // above and this insert — fall back to the idempotent response instead
+      // of surfacing a raw 500 for what is, from the client's perspective, a
+      // successful (already-processed) submission.
+      if (e instanceof Error && e.message.includes('UNIQUE') && e.message.includes('client_uuid')) {
+        const race = findByUuid();
+        if (race) {
+          const res: CreateTransactionResponse = { id: race.id, total_cents: race.total_cents };
+          return res;
+        }
       }
-      return id;
-    })();
+      throw e;
+    }
 
     const res: CreateTransactionResponse = { id: txId, total_cents: paidTotal };
     return res;