API : AI quota : Automatic AI top-up

This request sets the automatic AI top-up of a customer (portal: customer details, under AI product): an AI top-up product that the API buys by itself every time one of the customer's AI resources (transcription, summary, text to speech) reaches 80 % of what is available for the month - so the allowance never runs out. Send null to stop buying automatically.

How it works:

1. The trigger is the same moment the 80 % / 100 % usage warning is decided after each counted AI request (see AIUsageCounters notified). It is claimed atomically, and only on current numbers. A single request that jumps straight past 100 % triggers it too.
2. One API server buys at a time per customer (Redis lock aiAutoTopUp:lock:<customer id>, 60 s expiry), and every purchase is decided on the usage and limit as they are right then - so overlapping requests never buy more than the usage needs. Nothing is bought into the next month for a crossing at the end of a month.
3. The top-up is bought exactly like Buy top-up does it - credit first, a locked invoice line, a reseller invoice line, re-armed warnings, the change log and the recording catch-up. The invoice line description starts with AI top-up (automatisk), and the change log entry AI top-up bought automatically names the employee who set the automatic top-up up, impersonated by the system.
4. It is bought again and again until the resource is below 80 % of the raised limit - at most 10 times per crossing, which only a top-up far too small for the usage ever reaches (logged as a warning). It is bought again at every later crossing in the month; there is no monthly cap.
5. The usage-limit subscribers (employees with notifyOnGeneralUsageLimit on the customer, notifyOnGeneralUsageLimitReseller on the reseller) get the e-mail ai_auto_topup.html / ai_auto_topup_reseller.html - what was bought, how many times, the price of one and the usage after it - instead of the 80 % / 100 % warning, which the raised limit has made untrue.
6. When the purchase fails - the product has ended, been deleted or no longer fits the customer's AI product, or the customer is not active - the failure is logged to syslog (ai-auto-topup: … failed) and the ordinary 80 % / 100 % warning is sent as before. Quota status reports such a top-up with available: false.
7. When the customer moves to another reseller the automatic top-up is removed - it names a product from the old reseller's range.

The product must be one the user could buy for the customer right now: it must be among the Top-up products for this user and customer (so a customer OWNER cannot choose a reseller-only product, a RESELLER can). The setting is stored as finance.aiAutoTopUp on Customers and is never taken from a customer update.

{ "product": "650000000000000000000420" }
{ "product": null }

{
  "success": true,
  "autoTopUp": {
    "_id": "650000000000000000000420",
    "name": "AI top-up: 5 hours transcription",
    "price": 199.00,
    "aiTopUp": { "sttSeconds": 18000, "llmTokens": 0, "ttsCharacters": 0 },
    "from": "2026-10-25T12:00:00.000Z",
    "available": true
  }
}