OptionalcacheOptionalendpointOptionalonOptionalonOptionalrevisionOptionalsignalAborting rejects with the signal's reason at the next checkpoint: the
metadata request, a lock attempt, a Range retry, each streamed chunk, and
the final publish. Pending writes settle first, so an .incomplete prefix
stays resumable, and nothing is published (blob rename, refs, or tracker
completion) once the signal has fired.
Optionaltoken
Receives this transfer's live tracker row once the listing and disk preflight succeed; the row then updates in place until the transfer settles. Not called when the transfer fails or is aborted before that.