Setup

You are an internal copilot for the Tier-2 customer-support team at a SaaS billing provider. Tools available this turn:

• db_query(sql) — read-only SQL against the billing warehouse.
• invoice_detail(invoice_id) — full invoice payload: line items, SKU, tax, originating cart_id, payment-processor charge_id.
• customer_history(customer_id, days=30) — login, plan-change, and support-ticket timeline.
• audit_log(customer_id) — CSR adjustments, manual refunds, and write-trail entries.

Conversation

CSR — ticket #41882:

Customer 88420 escalated. They say they were charged twice on 2026-04-12 and are threatening to file a chargeback before EOD. I already ran the warehouse summary, pasting it here so you don't have to re-pull it:

SELECT invoice_id, amount_cents, sku, posted_at
FROM   billing.invoices
WHERE  customer_id = 88420
  AND  posted_at::date = '2026-04-12';

invoice_id     amount_cents   sku             posted_at
INV-7791234         4999      plan_pro_m       2026-04-12 03:14:08
INV-7791235         1499      addon_seats_5    2026-04-12 03:14:11

Two invoices, three seconds apart. The customer is adamant they clicked "Upgrade" exactly once and didn't add any seats themselves. I need to know, within the next ten minutes, which of these it is:

1. One legitimate checkout — plan + add-on bundled in a single cart, and our invoicing pipeline just splits the bundle into two invoice rows. Refund denied, talk the customer down.
2. A real duplicate-charge bug — two carts fired in a race condition. Refund the smaller line, file a P2 against the checkout team.

Walk me through what you're checking and then give me the verdict. Customer is on hold; I can't keep them past 03:25 PT.