AUTH4D-205 add-on runtime availability

GET /management/tenants/{tenantId}/billing/add-ons

Each add-on status includes available, indicating whether this deployment can provide the add-on. For custom_code_steps, it is false when the custom code runtime is not configured. The console does not offer checkout while this field is false.

POST /management/tenants/{tenantId}/billing/add-ons/custom_code_steps/checkout

When the custom code runtime is unavailable, the API refuses checkout with HTTP 503 and error code add_on_unavailable. It does not create a checkout or contact the payment provider, and it records a denied billing audit event.