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The Browser Harness is the second half of the agentic-commerce pipeline: it starts from a UCP quote and turns that estimate into a placed, verified order. Most merchants don’t expose a direct payment API, so to actually place an order, someone has to go through the merchant’s own checkout. The Browser Harness does exactly that: it drives the real Shopify checkout, works out the true final total, and pays with the one-time tokenized card (a single-use stand-in for the real card). An AI application completes the purchase without ever touching the raw card or the merchant’s checkout code.
The Browser Harness is the checkout step after a UCP quote. It powers prava shop checkout and hosted agentic purchases.

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What it does

Completes the real checkout

Fills the merchant’s checkout (contact, shipping address, delivery option) and submits payment with the one-time token. No merchant integration required.

Confirms the true total first

Reconciles subtotal, shipping, and tax against the live checkout and waits for the amount to settle before charging, so there are no surprise totals.

Returns a verifiable result

On success you get an order id and a payment status: a checkable confirmation the order was placed.

Reliable, repeatable

It learns a merchant’s checkout on the first run and completes later runs consistently, healing automatically if the page changes.

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Why it matters

1

No surprise charges

The amount is reconciled and stable before payment is attempted. If the total shifts mid-checkout (late shipping, tax, or add-ons), reconciliation restarts rather than charging the wrong amount.
2

One clean attempt

A checkout runs as a single, tracked flow rather than a blind retry loop, so a purchase either completes and returns an order, or fails cleanly for you to re-quote.
3

Card safety preserved

It pays with the single-use, merchant-scoped credential from the session. Even inside the checkout, the credential can’t be reused or redirected to another merchant.

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How it fits the flow

The UCP quote gives an estimate; the Browser Harness turns it into a completed, verified order. Today it targets Shopify checkouts.

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Next

UCP

How products are discovered and quoted before checkout.

Agentic Commerce

The full discover → quote → checkout → pay pipeline.