fix(futures): MARKET cap uses discovered price (part of #126)

src/execution/futures.ts

@@ -1405,10 +1405,17 @@ export function createFuturesExecutionService(config: FuturesConfig): FuturesExe
   const maxPositionSize = config.maxPositionSize ?? 10000; // $10k default
 
   async function resolveOrderPrice(request: FuturesOrderRequest): Promise<number> {
-    if (request.price !== undefined && Number.isFinite(request.price) && request.price > 0) {
+    // MARKET orders fill at the venue's current price, which the exchange
+    // determines at execution time. A caller-supplied price is never forwarded
+    // for MARKET submissions (see placeBinanceFuturesOrder), so trusting it
+    // here would let a low `price` shrink the notional cap check while the
+    // order still fills at market. MARKET (and orderType-less, which submits
+    // as MARKET) must therefore value exclusively off discovered price.
+    const isMarketOrder = request.orderType === undefined || request.orderType === 'MARKET';
+    if (!isMarketOrder && request.price !== undefined && Number.isFinite(request.price) && request.price > 0) {
       return request.price;
     }
-    if (request.stopPrice !== undefined && Number.isFinite(request.stopPrice) && request.stopPrice > 0) {
+    if (!isMarketOrder && request.stopPrice !== undefined && Number.isFinite(request.stopPrice) && request.stopPrice > 0) {
       return request.stopPrice;
     }
 
@@ -1452,7 +1459,12 @@ export function createFuturesExecutionService(config: FuturesConfig): FuturesExe
       try {
         if (request.platform === 'mexc' && config.mexc) {
           const valuation = await getMexcOrderValuation(config.mexc, request.symbol);
-          checkPrice = request.price ?? request.stopPrice ?? valuation.price;
+          // Same MARKET rule as resolveOrderPrice: caller price is never the
+          // fill price for MARKET orders, so the cap must use venue price.
+          const isMarketOrder = request.orderType === undefined || request.orderType === 'MARKET';
+          checkPrice = isMarketOrder
+            ? valuation.price
+            : request.price ?? request.stopPrice ?? valuation.price;
           contractSize = valuation.contractSize;
         } else {
           checkPrice = await resolveOrderPrice(request);

tests/trading/futures-pre-trade.test.ts

@@ -98,4 +98,32 @@ describe('futures pre-trade enforcement', () => {
       globalThis.fetch = originalFetch;
     }
   });
+
+  it('ignores caller-supplied price for MARKET notional cap (#126)', async () => {
+    configurePreTradeGate({ maxOrderSize: 1000 });
+    const originalFetch = globalThis.fetch;
+    // Venue discovers BTC at $60,000: 1 BTC = $60,000 notional > $1,000 cap.
+    // A caller-smuggled `price: 1` must not shrink the cap check to $1.
+    globalThis.fetch = async () =>
+      new Response(JSON.stringify({ markPrice: '60000' }), { status: 200 });
+
+    try {
+      const service = createFuturesExecutionService({
+        binance: { apiKey: 'test', secretKey: 'test' },
+        dryRun: true,
+      });
+      const result = await service.placeMarketOrder({
+        platform: 'binance',
+        symbol: 'BTCUSDT',
+        side: 'long',
+        size: 1,
+        price: 1,
+      } as unknown as Omit<Parameters<typeof service.placeMarketOrder>[0], 'price'>);
+
+      assert.equal(result.success, false);
+      assert.match(result.error ?? '', /exceeds max \$1000/);
+    } finally {
+      globalThis.fetch = originalFetch;
+    }
+  });
 });