getHeaders adds host headers to every request, read per request and on the 401 retry, for example a request id for tracing. The SDK's own Content-Type, Authorization, X-Tenant-Id and Accept-Language win over a host header of the same name in any letter case.
fetch replaces the global fetch the client sends with. It is called unbound, so window.fetch can be passed as is.
feature_disabled is listed among the known server codes: Aria answers it with 403 when AI is switched off for the tenant.

An error body of the form { "error": { "code", "message" } } now fills serverCode and serverMessage like the flat { "error", "message" } envelope. Before, both stayed null for it.

@revenexx/aria-sdk v0.4.0