Redeem a license key on a customer's behalf

Server-to-server redemption — the primitive behind a Discord /redeem command or a panel's "add time" box. Identical semantics to redeeming in the loader: the same validation, the same protection against consuming a key that grants nothing, and the same license.used webhook.

Renewal works even when the subscription has already lapsed; time is added from now rather than from the old expiry.

### Tiers

A subscription is a single record with one level and one clock, so a key is only applied when the result is unambiguous:

- Higher tier — upgrades, and keeps the remaining time. - Same tier — extends. - Lower tier, subscription still active — refused as TIER_DOWNGRADE and *not consumed*. Extending at the higher tier would let cheap keys renew an expensive tier; dropping the tier would take away something already paid for. The key stays valid and works once the current subscription lapses. - Lower tier, subscription lapsed — accepted, and the key's tier applies from scratch. - Timed key against a lifetime subscription — refused as TIER_CONFLICT and not consumed, since "higher tier for 30 days, then back to lifetime" cannot be represented.

{
  "licenseKey": "ABCD-EFGH-IJKL-MNOP"
}

{
  "success": true,
  "message": "Subscription updated",
  "data": {
    "appId": "864a...",
    "appName": "Lunar",
    "extended": true,
    "subscriptionLevel": 2,
    "subscriptionName": "Pro",
    "expiresAt": "2026-10-01T00:00:00.000Z"
  }
}

{
  "error": "This key provides no additional benefit for the current subscription",
  "code": "NO_BENEFIT"
}

{
  "error": "This key is for a lower tier than the current subscription. It has not been used — redeem it once the current subscription expires.",
  "code": "TIER_DOWNGRADE"
}

{
  "error": "A timed key cannot upgrade a lifetime subscription. It has not been used — a lifetime key of the higher tier is required.",
  "code": "TIER_CONFLICT"
}

{
  "error": "This license key is locked to different hardware",
  "code": "HWID_MISMATCH"
}

{
  "error": "License already redeemed",
  "code": "RACE_LOST"
}