diff --git a/src/core/order-coordinator.ts b/src/core/order-coordinator.ts
index 1bb36bf..a0caec4 100644
--- a/src/core/order-coordinator.ts
+++ b/src/core/order-coordinator.ts
@@ -89,7 +89,14 @@ export async function deduplicateOrders(
   side: string,
   log: LogHandler
 ): Promise<void> {
-  const sameTypeOrders = openOrders.filter((o) => o.type === type && o.side === side);
+  // Treat STOP orders on some exchanges (e.g., Lighter) as LIMIT with stopPrice populated.
+  const sameTypeOrders = openOrders.filter((o) => {
+    const normalizedType = String(o.type).toUpperCase();
+    const isStopLike = Number.isFinite(Number(o.stopPrice)) && Number(o.stopPrice) > 0;
+    const matchesStop = type === "STOP_MARKET" && isStopLike && o.side === side;
+    const exactMatch = normalizedType === type && o.side === side;
+    return exactMatch || matchesStop;
+  });
   if (sameTypeOrders.length <= 1) return;
   sameTypeOrders.sort((a, b) => {
     const ta = b.updateTime || b.time || 0;
@@ -241,7 +248,6 @@ export async function placeStopLossOrder(
   }
   const priceTick = opts?.priceTick ?? 0.1;
   const qtyStep = opts?.qtyStep ?? 0.001;
-  const isAster = String((adapter as any).id ?? "").toLowerCase() === "aster";
   const params: CreateOrderParams = {
     symbol,
     side,
@@ -249,14 +255,10 @@ export async function placeStopLossOrder(
     stopPrice: roundDownToTick(stopPrice, priceTick),
     closePosition: "true",
     timeInForce: "GTC",
-    // Do not round down stop quantity here to avoid underflow to exchange min; gateway will quantize precisely
     quantity,
     triggerType: "STOP_LOSS",
   };
-  // For Aster futures, STOP orders must not include reduceOnly; omit it specifically.
-  if (!isAster) {
-    params.reduceOnly = "true";
-  }
+
   // Avoid forcing price for STOP_MARKET globally; keep this exchange-specific in gateways
   await deduplicateOrders(adapter, symbol, openOrders, locks, timers, pendings, type, side, log);
   lockOperating(locks, timers, pendings, type, log);
@@ -299,8 +301,6 @@ export async function placeTrailingStopOrder(
     symbol,
     side,
     type,
-    // Do not round down trailing-stop quantity to avoid underflowing small positions to zero;
-    // let the exchange adapter handle precise quantization.
     quantity,
     reduceOnly: "true",
     activationPrice: roundDownToTick(activationPrice, priceTick),
@@ -351,8 +351,6 @@ export async function marketClose(
     side,
     type,
     quantity: safeQty,
-    reduceOnly: "true",
-    // Hint exchanges (like Paradex) to close the whole position and tolerate omitted size
     closePosition: "true",
   };
   await deduplicateOrders(adapter, symbol, openOrders, locks, timers, pendings, type, side, log);
diff --git a/src/exchanges/lighter/adapter.ts b/src/exchanges/lighter/adapter.ts
index 726432d..e00fe27 100644
--- a/src/exchanges/lighter/adapter.ts
+++ b/src/exchanges/lighter/adapter.ts
@@ -108,13 +108,14 @@ export class LighterExchangeAdapter implements ExchangeAdapter {
 
   async cancelOrder(params: { symbol: string; orderId: number | string }): Promise<void> {
     await this.ensureInitialized("cancelOrder");
-    await this.gateway.cancelOrder({ orderId: params.orderId });
+    // Accept both clientOrderId and order_index as strings; forward as-is to preserve precision
+    await this.gateway.cancelOrder({ orderId: String(params.orderId) });
   }
 
   async cancelOrders(params: { symbol: string; orderIdList: Array<number | string> }): Promise<void> {
     await this.ensureInitialized("cancelOrders");
     for (const orderId of params.orderIdList) {
-      await this.gateway.cancelOrder({ orderId });
+      await this.gateway.cancelOrder({ orderId: String(orderId) });
     }
   }
 
diff --git a/src/exchanges/lighter/gateway.ts b/src/exchanges/lighter/gateway.ts
index 99a652c..e74967c 100644
--- a/src/exchanges/lighter/gateway.ts
+++ b/src/exchanges/lighter/gateway.ts
@@ -312,7 +312,14 @@ export class LighterGateway {
     await this.ensureInitialized();
     const marketIndex = params.marketIndex ?? this.marketId;
     if (marketIndex == null) throw new Error("Market index unknown");
-    const indexValue = BigInt(typeof params.orderId === "string" ? Number(params.orderId) : params.orderId);
+    // Parse order id to BigInt without precision loss; prefer string input
+    let indexValue: bigint;
+    if (typeof params.orderId === "string") {
+      indexValue = BigInt(params.orderId);
+    } else {
+      // Fallback for numeric ids (may be unsafe if beyond 2^53-1)
+      indexValue = BigInt(Math.trunc(params.orderId));
+    }
     const { apiKeyIndex, nonce } = this.nonceManager.next();
     try {
       const signed = await this.signer.signCancelOrder({
@@ -323,6 +330,11 @@ export class LighterGateway {
       });
       const auth = await this.ensureAuthToken();
       await this.http.sendTransaction(signed.txType, signed.txInfo, { authToken: auth });
+      // Optimistically remove the order locally to avoid stale duplicates until WS confirms
+      const key = String(params.orderId);
+      this.orderMap.delete(key);
+      this.orders = Array.from(this.orderMap.values());
+      this.emitOrders();
     } catch (error) {
       this.nonceManager.acknowledgeFailure(apiKeyIndex);
       throw error;
diff --git a/src/exchanges/lighter/mappers.ts b/src/exchanges/lighter/mappers.ts
index 663ff11..5e4c21c 100644
--- a/src/exchanges/lighter/mappers.ts
+++ b/src/exchanges/lighter/mappers.ts
@@ -78,7 +78,8 @@ export function lighterOrderToAster(symbol: string, order: LighterOrder): AsterO
     ? "SELL"
     : "BUY";
   return {
-    orderId: order.order_index,
+    // Use string order id to avoid precision loss; prefer on-chain order_index for cancellation
+    orderId: String(order.order_index ?? order.client_order_index ?? ""),
     clientOrderId: String(order.client_order_index ?? order.order_index ?? ""),
     symbol,
     side,