The Flag That Fired Old Code — JavaScript Bug Hunt

Briefing

Inspired by Knight Capital's 2012 collapse: a decommissioned feature flag was repurposed, and servers still carrying the OLD code path blasted the market with orders. $460M gone in 45 minutes.

Here, the legacy module is locked (you can't delete it — that's the point). The router must treat the dead flag as dead and clamp order quantity, no matter what.

Bug report

BUG-KCG-2012 · Priority: Existential · Reported by: risk desk

Spec for route(order, flags):

• The "power_peg" flag is DEAD. Its presence must change nothing.
• Quantity is always clamped to MAX_QTY (100) — never more, never negative.
• Exactly ONE order comes out for one order in.

Observed: with the flag set, the legacy blaster emits 1000x child orders.

Logs

[router] flags=["power_peg"] in qty=50 -> out orders=50000 (!!)

The code as shipped

src/trade/router.js (editable)

var legacy = require("./legacy");

var MAX_QTY = 100;

// Routes one inbound order. flags is an array of active flag names.
exports.route = function (order, flags) {
  if (flags.indexOf("power_peg") !== -1) {
    return legacy.blast(order);
  }
  return [{ symbol: order.symbol, qty: order.qty }];
};

Read-only context: src/trade/legacy.js.