I build the software small businesses run on.

The client's rule was that no customer ever gets a message they did not ask for. So every send passes one gate, and there is no override flag for a bug or a bad prompt to flip.

// guard.ts (Masvingo Chicks WhatsApp assistant)
async function dmDecision(redis: Redis, number: string): Promise<SendDecision> {
  if (!/^\d{8,15}$/.test(number)) {
    return { allowed: false, reason: "not a personal number" };
  }
  if (isStaff(number)) return { allowed: true, reason: "staff" };

  const seen = await redis.get(inboundKey(number));
  if (!seen) {
    // The branch that makes an unsolicited customer message impossible.
    log.warn("blocked outbound to a number with no open inbound window", { number });
    return { allowed: false, reason: "no inbound message inside the reply window" };
  }
  if (expired(seen)) return { allowed: false, reason: "reply window expired" };

  return { allowed: true, reason: "reply" };
}

The WhatsApp bot reads a customer's message and fills in the details. It never writes a price. Every figure comes from one pure function that the website also uses, with its own tests.

// engine.js (The Draught Man): no I/O, runs in the browser and in the bot
export function planKegs({ guests, occasionId, beersPerGuestOverride, kegsOverride }) {
  const occasion = OCCASION_BY_ID[occasionId];
  const perKeg = servingsPerKeg();

  const recommendedPerGuest =
    beersPerGuestOverride != null ? beersPerGuestOverride
    : occasion ? occasion.recommendedBeersPerGuest : 4;

  const recommendedKegs = Math.max(1, Math.ceil((guests * recommendedPerGuest) / perKeg));
  const kegs = kegsOverride != null ? Math.max(1, Math.floor(kegsOverride)) : recommendedKegs;

  return { perKeg, recommendedKegs, kegs, servingsSupplied: kegs * perKeg };
}

Customers started receiving each other's quotes. The database lookup combined its two conditions with OR by default, so every contact matched the same open conversation. The fix was one setting, applied to every filtered lookup so it cannot come back.

// Find Conversation, simplified. Before: the default, invisible in the export
{ "conditions": ["contact_id = :contact", "is_active = true"] }
// matched: contact_id = :contact OR is_active = true

// after
{ "conditions": ["contact_id = :contact", "is_active = true"],
  "matchType": "allFilters" }
// matched: contact_id = :contact AND is_active = true

I tested whether copying top crypto traders could pay after fees. The answer was no, so I switched it off and wrote down why, before any real money went in.

# Research summary (copy-trading study, Sept to Oct 2026)
wallets on the leaderboard          47,095
wallets with enough history          5,636
survived multiple-testing check         11
basket paper-traded for 2 weeks         10
entry batches                           35
mean result per trade, after fees   -1.25%

# Verdict: their edge is real, but not catchable an hour late. Stopped.