OptionalfetchOptionalheadersExtra headers sent with each request.
OptionaltimeoutRequest timeout in milliseconds. Uses AbortSignal.timeout under the hood.
OptionalvalidatePredicate to decide which HTTP status codes resolve and which reject.
Defaults to status >= 200 && status < 300.
Additional RequestInit fields forwarded to fetch (e.g. credentials, mode, cache). Ignored: method, body, headers, signal — those are managed by the adapter.