OptionalbaseOptionalfetchInjected fetch — defaults to the global. Tests pass a recording mock.
Optionalinit: RequestInitOptionalactionThe current frontend ACTION (a button-click id), sent as x-suluk-action on every request so the
server's cost meter (@suluk/cost) can attribute cost back to the UI action. A function lets it reflect
the live action. A per-call action on .mutate({ action }) overrides it.
Prepended to every built URL (e.g. "https://api.example.com").