diff --git a/lib/auto-trade.ts b/lib/auto-trade.ts
index 9a890c3..161192b 100644
--- a/lib/auto-trade.ts
+++ b/lib/auto-trade.ts
@@ -1373,8 +1373,9 @@ async function copyTradeLocked(lease: number, lane: string): Promise<unknown[]>
  * The one rule it overrides is "one trade per day" for unsplit accounts: an
  * account that already booked something today may take another leg toward
  * what's left of its target. Everything else still applies — flat, history
- * loaded, the daily-loss room, the firm's trading hours, its lane flat and
- * no batch in flight there.
+ * loaded, the daily-loss room, the firm's trading hours, no batch in flight
+ * in its lane — and a lane with positions open is only joined on the same
+ * instrument and side.
  */
 export async function fireManualLeg(accountId: number, action: 'Buy' | 'Sell' | 'Auto'): Promise<LegResult> {
     const found = firmClients().ready.find(({ client }) => client.accountList.some((a) => a.id === accountId));
@@ -1398,14 +1399,28 @@ export async function fireManualLeg(accountId: number, action: 'Buy' | 'Sell' |
         room = gate.room;
     }
 
+    // A lane with positions open may only be joined on the same instrument
+    // and side — what a batch of like accounts would have done — never the
+    // other side (that is hedging).
     const lane = laneOf(firm);
-    const open = countOpenPositions(inLane(firmClients().ready, lane));
-    if (open > 0) throw new Error(`${open} position(s) still open in the ${laneName(lane)} lane`);
+    const held = inLane(firmClients().ready, lane).flatMap(({ client: c }) => c.accountList
+        .map((a) => c.positions[a.id])
+        .filter((p): p is NonNullable<typeof p> => !!p));
+    const heldSides = new Set(held.map((p) => (p.netPos > 0 ? 'Buy' : 'Sell')));
+    const heldContracts = new Set(held.map((p) => String(p.contractId)));
+    if (heldSides.size > 1 || heldContracts.size > 1) throw new Error(`the ${laneName(lane)} lane holds mixed positions — not adding to it`);
+    const heldSide: 'Buy' | 'Sell' | null = held.length > 0 ? (held[0].netPos > 0 ? 'Buy' : 'Sell') : null;
+    if (heldSide && action !== 'Auto' && action !== heldSide) {
+        throw new Error(`the ${laneName(lane)} lane is ${heldSide === 'Buy' ? 'long' : 'short'} — a ${action} would hedge it`);
+    }
     const state = getState();
     const symbol = state.symbol !== 'Auto' ? state.symbol : 'NQ';
-    const resolvedAction: 'Buy' | 'Sell' = action === 'Auto' ? (Math.random() < 0.5 ? 'Buy' : 'Sell') : action;
+    const resolvedAction: 'Buy' | 'Sell' = heldSide ?? (action === 'Auto' ? (Math.random() < 0.5 ? 'Buy' : 'Sell') : action);
     const contract = await client.findFrontMonthContract(symbol);
     if (!contract) throw new Error(`no instrument for ${symbol}`);
+    if (held.length > 0 && String(contract.id) !== [...heldContracts][0]) {
+        throw new Error(`the ${laneName(lane)} lane holds ${[...heldContracts][0]}, not ${contract.id} — not adding to it`);
+    }
     const pv = contract.pointValue ?? POINT_VALUES[symbol];
     if (!pv) throw new Error(`no point value for ${symbol}`);