One side per machine: no lane opens against a position another lane holds

Each lane chose its batch's side on its own coin flip. So one person's
machine could be long NQ in the futures lane while its Vest accounts sat
short NDX, hedging that person against themselves across firms.

- Every new entry now takes the side of whatever the machine holds in any
  lane (machineSide in trading-logic). That includes another firm's
  positions and hand trades on any of the machine's accounts.
- With positions on both sides already, nothing is added: the batch reports
  positions-open with the reason, and a manual leg is refused.
- A side chosen with nothing held is reserved while its batch places it, so
  a lane deciding meanwhile follows it.
- It works on the side, not the instrument: NQ against an NDX perp is the
  same bet, and the indices and crypto are close enough that one side for
  everything is the only rule that never hedges.
- Unchanged: one direction per batch within a lane, and the DXtrade and Vest
  clients' own guards against opening opposite another of their accounts.
  The fleet still doesn't coordinate sides across people.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

lib/auto-trade.ts

@@ -18,7 +18,7 @@ import {
     BIG_DAY_THRESHOLD, LEG_COMPLETION_EPSILON, MAX_LEGS_PER_DAY,
     FALLBACK_COMMISSION_PER_CONTRACT, MAX_COMMISSION_PER_CONTRACT, DLL_MIN_STOP,
     CME_EVENING_OPEN_MIN, foldReason, withinFirmCaps,
-    fundRowsKey, markFinishedCycle, unbookedPayoutDrop,
+    fundRowsKey, markFinishedCycle, unbookedPayoutDrop, machineSide,
     type DayPlan, type FinishedCycleMark,
 } from './trading-logic';
 import { getSetting, setSetting, loadAccountMeta, saveAccountMeta } from './db';
@@ -65,6 +65,10 @@ interface TradeRuntime {
     /** Lane → when the batch holding that lane's trade mutex took it (absent
      *  = no batch in flight there). See laneOf. */
     tradeInFlight?: Map<string, number>;
+    /** The side a lane's batch (or manual leg) chose with nothing held on the
+     *  machine, while it places it: another lane deciding meanwhile takes the
+     *  same side (see sideForEntry). Only counts while its lease holds. */
+    sideReservation?: { side: 'Buy' | 'Sell'; lane: string; lease: number };
     /** Accounts whose exit the broker refused — a bracket while a hard daily
      *  loss limit was on, or a lone take-profit: the position was flattened
      *  and the account sits out the trade date rather than bleed a round trip
@@ -453,6 +457,32 @@ function holdsTradeMutex(lease: number, lane: string): boolean {
  *  release the batch that took over from it. */
 function releaseTradeMutex(lease: number, lane: string): void {
     if (holdsTradeMutex(lease, lane)) runtime().tradeInFlight?.delete(lane);
+    const r = runtime().sideReservation;
+    if (r && r.lane === lane && r.lease === lease) runtime().sideReservation = undefined;
+}
+
+/**
+ * The side a new entry in `lane` must take (machineSide): the side of every
+ * position on this machine in any lane, else the side another lane's batch is
+ * placing right now. One person's machine must never be long in one firm and
+ * short in another, whatever the instruments.
+ */
+function sideForEntry(lane: string): 'Buy' | 'Sell' | 'mixed' | null {
+    const net = firmClients().ready.flatMap(({ client }) => client.accountList
+        .map((a) => (client.positions[a.id]?.netPos ?? 0) as number)
+        .filter((n) => n !== 0));
+    const r = runtime().sideReservation;
+    const reserved = r && r.lane !== lane && holdsTradeMutex(r.lease, r.lane) ? r.side : null;
+    return machineSide(net, reserved);
+}
+
+/** Why `action` can't be entered in `lane` without a hedge, or null. */
+function hedgeBlock(side: ReturnType<typeof sideForEntry>, action: 'Buy' | 'Sell' | 'Auto'): string | null {
+    if (side === 'mixed') return 'this machine holds long and short positions — no side to join until one of them closes';
+    if (side && action !== 'Auto' && action !== side) {
+        return `this machine is ${side === 'Buy' ? 'long' : 'short'} elsewhere — a ${action} would hedge it`;
+    }
+    return null;
 }
 
 /** What a firm's tiny legs (drain, extra-day) trade: a futures firm the
@@ -973,10 +1003,21 @@ async function runTradeLocked(
     }
     const open = laneReady.filter(({ firm }) => !isInNoTradeWindow(firm));
 
-    // One direction per batch: every account trades the same side.
-    const resolvedAction: 'Buy' | 'Sell' = action === 'Auto'
-        ? (Math.random() < 0.5 ? 'Buy' : 'Sell')
-        : action;
+    // One direction per batch, and per machine: every account trades the side
+    // of whatever this machine already holds in any lane (another firm, a hand
+    // trade), so nothing the batch opens hedges the person against themselves.
+    // Free only when nothing is held or being placed; the choice is then held
+    // while the batch places it, so a lane deciding meanwhile follows it.
+    const side = sideForEntry(lane);
+    const blocked = hedgeBlock(side, action);
+    if (blocked) {
+        console.log(`[auto-trade] ${laneName(lane)}: ${blocked} — skipping`);
+        return { outcome: 'positions-open', results: [], detail: blocked };
+    }
+    const resolvedAction: 'Buy' | 'Sell' = side === 'Buy' || side === 'Sell'
+        ? side
+        : action === 'Auto' ? (Math.random() < 0.5 ? 'Buy' : 'Sell') : action;
+    if (!side) runtime().sideReservation = { side: resolvedAction, lane, lease };
     const futuresLane = lane === FUTURES_LANE;
     // An explicit symbol (the scheduler's, or a manual Trade) is the
     // operator's pick; 'Auto' is drawn per batch from the batch firm's list.
@@ -1826,7 +1867,13 @@ export async function fireManualLeg(accountId: number, action: 'Buy' | 'Sell' |
         if (heldSide && action !== 'Auto' && action !== heldSide) {
             throw new Error(`the ${laneName(lane)} lane is ${heldSide === 'Buy' ? 'long' : 'short'} — a ${action} would hedge it`);
         }
-        const resolvedAction: 'Buy' | 'Sell' = heldSide ?? (action === 'Auto' ? (Math.random() < 0.5 ? 'Buy' : 'Sell') : action);
+        // …nor against what the machine holds in any other lane.
+        const side = sideForEntry(lane);
+        const blocked = hedgeBlock(side, heldSide ?? action);
+        if (blocked) throw new Error(blocked);
+        const resolvedAction: 'Buy' | 'Sell' = heldSide
+            ?? (side === 'Buy' || side === 'Sell' ? side : action === 'Auto' ? (Math.random() < 0.5 ? 'Buy' : 'Sell') : action);
+        if (!side) runtime().sideReservation = { side: resolvedAction, lane, lease };
         const sizingItem: SizingItem = {
             firmName: firm.name, firm, client, acc,
             cash: ev.cash, dailyPnL: ev.dailyPnL, plan: ev.plan, drain: ev.drain,