Session URL, stream, and platform-specific error mapping.
OptionalstartOffset?: numberOptionalstreamStartsAtOffset?: booleanWhen true (default), stream already begins at startOffset (e.g. R2 Range GET). When false, bytes before startOffset are read from stream and discarded.
OptionalonBytesConfirmed?: (bytesConfirmed: number) => Promise<void>Optionalsignal?: AbortSignalPlatform upload result on success or failure.
Resumable upload in 256 KiB–aligned chunks (Google's recommended protocol). When startOffset is greater than zero, stream must already begin at that byte index unless streamStartsAtOffset is false (non-seekable sources).