OptionalfetchImpl?: FetchLikeOptionalmaxConcurrency?: numberOptionalsignal?: AbortSignalOptionaltransportController?: AbortControllerReuse one fetch-visible cancellation identity across sequential stages. The controller must not be shared with unrelated loading operations.
Fetch and verify acceptance-only sources before giving them canonical lazy transport identities. This never treats the source URL as VFS authority: only the separately declared HTTPS URL, digest, and size survive. A caller abort or first source failure stops new work and closes every active body before the loader rejects with that exact first reason.