How it works

Nothing here is hidden. Every shopkeeper works out its own options, scores them, and has the result checked against its spending rules before a single coin moves. This is that, taken apart.

A worked example

One turn, start to finish

Tick 40. The bakery is out of flour, and Bram is due a decision. Everything below is on screen while it happens — the town does not write it up afterwards.

1 · What Bram could see

The town puts this in plain words. The same six lines go to the inspector and, on the turns where a model is asked, to the model — there is no second, hidden version.

Bram the Baker has 18.70 USDC to spend and 6.30 USDC left in this stretch's budget.
Carrying nothing.
The Bakery has 4 bread at 0.36 USDC.
Recipe: 2 flour makes 4 bread, once every 4 ticks. Last worked 2 ticks ago.
Bram cannot work without flour — 2 short of a batch. Cheapest is The Mill at 0.45 USDC (6 left).
Bram likes to keep 2 bread on hand and has 4 out front. Nothing pressing there.

2 · The five things he could have done

Every move open to him, scored from 0 to 1. The town keeps the ones it threw out, which is what makes the choice readable rather than magical.

Buy 2 Flour from The MillChosen0.76

Bram cannot work without flour — 2 short of a batch. The Mill has 6 at 0.45 USDC each, at or under the usual 0.45 USDC. Total 0.90 USDC.

Raise Bread to 0.39 USDC0.36

Only 4 left on the shelf, so Bram can ask more than 0.36 USDC.

Wait and see0.15

Always available. Wins only when nothing else is worth doing.

Make 3 bread0.00

Needs 2 flour and has 0.

Buy Meal0.00

Nobody in town is selling meal right now.

3 · Why the flour won

Flour scored 0.76 because Bram cannot bake without it — an urgent need, at a price that is exactly the usual one. Raising the price of bread came second at 0.36. A gap of 0.40 is far past the 0.25 the town needs to call a choice obvious, so Bram acted on it himself.

“Buy 2 Flour from The Mill” scored 0.76 against 0.36 for the next best — clear enough to act without asking anyone.

No model was asked. This turn cost nothing, and most turns in the town look like it.

4 · The seven rules that checked the payment

0.90 USDC from Bram to Odette. Every rule reports back, including the ones that had nothing to complain about.

Town circuit breakerThe town is running, so payments are allowed.

Passed

Bram's statusBram is trading normally.

Passed

Spending switchBram's spending is switched on.

Passed

Per-purchase limit0.90 USDC is inside the 4.00 USDC limit for a single purchase.

Passed

Budget for this stretch6.60 USDC of 12.00 USDC used once this goes through.

Passed

Approved payeeOdette is on Bram's approved list.

Passed

Money on handBram holds 18.70 USDC that is not already committed.

Passed

5 · What happened

Deciding to spend and spending are separate. Bram has to walk there first, and the money is held back the whole time.

Tick 40

Bram is off to The Mill for 2 flour.

0.90 USDC set aside. Every spending rule passed.

Ticks 41–49

Bram walks the nine tiles west to the mill.

The 0.90 stays held back the whole way, so his spendable balance reads 17.80 while he is on the road.

Tick 49

Bram agreed to buy 2 flour from Odette for 0.90 USDC.

Odette was still asking 0.45, inside the 0.47 Bram set out willing to pay, and all seven rules ran again and passed. Had she raised her price — or had anyone tightened Bram's limit while he walked — he would have been stopped at the door and the 0.90 would have gone straight back to him.

Tick 50

Bram's payment of 0.90 USDC to Odette is on its way.

It takes three ticks to clear, and you watch it do it.

Tick 52

Bram paid Odette 0.90 USDC for 2 flour.

Balance 17.80. Spent this stretch, 7.20 of 20.00. The flour bin is full enough to bake again.

Three ways to decide

A model is the last resort, not the first

Every shopkeeper scores its options first. What happens next depends entirely on how close the top two came.

Reflex

One option is clearly ahead.

No cost

When it happens

The best option scores more than 0.25 above the next best — or there is only one thing worth doing at all. Bram out of flour with the mill open is this every time.

What it costs

Nothing. No model is asked, nothing leaves the machine, and the answer is there the moment the scoring is finished.

Most of a shopkeeper's day is reflex, which is the point — you do not pay a model to notice an empty flour bin.

Habit

Close call, but reasoning is off.

No cost

When it happens

The top two options are within 0.25 of each other, and either reasoning is switched off in the controls or no OpenAI key is set.

What it costs

Nothing. The shopkeeper falls back on its own scoring and takes the top option.

The town says so plainly rather than quietly pretending it thought about it — the inspector shows both scores and the reason it did not ask.

Reasoned

Close call, and a key is set.

Costs money

When it happens

The top two are within 0.25 and reasoning is on. The shopkeeper is handed a shortlist of at most five options and asked to pick one by number.

What it costs

A fraction of a cent per turn on gpt-5-mini. The running total, the tokens and the round-trip time sit next to the decision in the inspector.

It gets the same lines you can read yourself, and it answers with a number, a sentence of reasoning, and something to say out loud.

The model only ever picks a number

It chooses from a list the town has already worked out, priced and checked. It cannot name a payee, invent an amount, set a price or add an option, so nothing it reads can talk it into a payment the spending rules would not have allowed anyway.

Spending rules

Seven checks, every purchase

These run the moment a shopkeeper commits to a purchase, and they all report back — the ones that passed as well as the one that did not. Watching the rules work is the point, not only watching them fire.

The rule	What it asks	What happens when it fails
Town circuit breaker	Is the town running, or has someone stopped it?	No payment opens anywhere in town until it is running again. This is the one switch that reaches every shopkeeper at once.
Bram's status	Is this shopkeeper trading, or has it been suspended?	This shopkeeper buys nothing until it is reinstated. Everyone else carries on around it.
Spending switch	Has this shopkeeper's spending been left switched on?	The purchase is dropped. Switching spending back on by hand is the only way through — no amount of wanting it helps.
Per-purchase limit	Is this one payment inside the shopkeeper's ceiling for a single purchase?	Stopped, with the amount and the ceiling written out side by side. Bram starts on 4 USDC. Drop it before he sets off and his flour run shrinks to fit; drop it while he is walking and it is stopped at the door.
Budget for this stretch	Does everything already spent, plus everything held for payments in flight, plus this, stay under the budget?	Stopped until the budget period rolls over. Money already committed to a payment on its way counts against the budget straight away, not when it clears.
Approved payee	Is this seller on the shopkeeper's approved list?	Stopped. Everyone in town is on everyone else's list and nobody outside it is, so an address the town has never heard of can never be paid.
Money on hand	Is there enough in the wallet that is not already committed elsewhere?	Stopped. Money held back for a payment already on its way is not available to spend twice.

The second rule carries whoever is buying — Bram’s status, Odette’s status, Pike’s status. And a purchase that clears all seven still is not final: the shopkeeper has to walk to the shop, and every one of them runs again on arrival, against the shelf and the limits as they stand by the time it gets there.

The moving parts

Five things, and nothing hidden behind them

Markette is a town whose shopkeepers hold wallets. Here is everything that makes one of them spend money.

ReservedOn its wayCleared

The town clock

A tick a second, and everything in a fixed order.

Each tick, payments move one step along, everyone walks a tile, deals are struck by whoever has arrived somewhere, everyone eats if they are due, and then whichever shopkeepers are up make a decision.

A shopkeeper decides roughly every six ticks and a payment clears in three, so there is always something in flight to look at. Leave the tab open overnight and the town catches up a bounded number of ticks rather than trying to replay the whole night at once.

The scorer

Pure, deterministic, and seeded.

It lists everything a shopkeeper could legally do right now — buy this, make that, put stock on the shelf, change a price, wait — and gives each one a number between 0 and 1, along with a sentence saying why.

Same seed, same town, every time. A strange run is reportable as a seed and a tick number, and it will do exactly the same thing again.

The model

It only ever picks a number from a list.

On a close call it gets the shortlist, already worked out and already priced, and returns one option number, one sentence of reasoning, and a line to say out loud.

It cannot name a payee, invent an amount, set a price or add an option that was not on the list. Whatever it picks still goes through the spending rules like anything else.

The spending rules

Checked on the way out, and checked again on arrival.

Seven rules run when a purchase is decided. Only if all seven pass does the shopkeeper set off, with the money held back from the moment it picks up its coat.

Then it walks, and things move while people walk. On arrival the whole thing is checked again — the shelf as it now stands, and all seven spending rules a second time. So a limit you tighten, a wallet you freeze or a town you stop while a shopkeeper is still on the road all catch it at the door. Whenever it is stopped, the held-back money goes straight back.

The ledger

Reserved, on its way, cleared — and you watch it happen.

Money never teleports. It is held back when the errand starts, the payment is opened when the deal is struck, it spends a few ticks travelling, and only then does it leave one wallet and land in the other.

Goods move when the payment clears, not before. With no chain configured the payments are simulated and labelled as such, down to a reference that could never be mistaken for a real transaction hash; point it at Base Sepolia and the same three stages carry real transfers.

Try this

Four things to do while it runs

The town is easier to believe once you have broken it on purpose.

Tighten a limit while someone is walking

Watch the People tab until someone sets off — a dotted line runs from them to the shop. Set their per-purchase limit to 0.50 USDC before they get there.

They arrive, the rules run again, and the purchase is stopped at the door — the amount they wanted and the ceiling they could not get past written out side by side, and the money they had set aside handed straight back. Leave the limit low and their next run simply shrinks to fit instead.

Hit Stop everything

Stop the town while a payment is halfway through and nothing finishes: whatever was on its way stays exactly where it was, and the money behind it stays held back.

Every new purchase fails on the first rule with the same line — the town is not running, so no money moves — and one click starts it all again from where it stood.

Turn reasoning on

Flip reasoning on with a key set, then watch which decisions change colour: only the close calls start going to a model, and the running cost begins ticking up a fraction of a cent at a time.

Open one of them and you get the tokens, the round-trip time, the exact shortlist the model saw, and the sentence it gave for its choice.

Step one tick at a time

Pause the town, advance a single tick, and open the newest decision in the inspector.

You get one shopkeeper's whole turn in order — what it could see, every option it weighed with its score, why one won, all seven rules with their verdicts, and what it actually did.

The rule

What it asks

What happens when it fails

Town circuit breaker

Is the town running, or has someone stopped it?

No payment opens anywhere in town until it is running again. This is the one switch that reaches every shopkeeper at once.

Bram's status

Is this shopkeeper trading, or has it been suspended?

This shopkeeper buys nothing until it is reinstated. Everyone else carries on around it.

Spending switch

Has this shopkeeper's spending been left switched on?

The purchase is dropped. Switching spending back on by hand is the only way through — no amount of wanting it helps.

Per-purchase limit

Is this one payment inside the shopkeeper's ceiling for a single purchase?

Stopped, with the amount and the ceiling written out side by side. Bram starts on 4 USDC. Drop it before he sets off and his flour run shrinks to fit; drop it while he is walking and it is stopped at the door.

Budget for this stretch

Does everything already spent, plus everything held for payments in flight, plus this, stay under the budget?

Stopped until the budget period rolls over. Money already committed to a payment on its way counts against the budget straight away, not when it clears.

Approved payee

Is this seller on the shopkeeper's approved list?

Stopped. Everyone in town is on everyone else's list and nobody outside it is, so an address the town has never heard of can never be paid.

Money on hand

Is there enough in the wallet that is not already committed elsewhere?

Stopped. Money held back for a payment already on its way is not available to spend twice.