Thrown by IHttpClient.request() when the server returns a non-2xx status.

TBody is the parsed error payload. It defaults to unknown, so the bare name HttpClientError keeps meaning exactly what it did and every existing catch (e) { if (e instanceof HttpClientError) … } is unaffected. A generated client narrows it through its own per-operation error guard, which is how a document's declared 4xx schemas reach the caller — the throw site itself cannot know which operation it is serving.