the node lines alone, what an exported namespace's digest covers (the header carries a timestamp)
the image: the lines, gzip-compressed
OptionalsourceLength: numberthe uncompressed lines, header first, trailer last; the header is encoded here because the length of the source is only known once every chunk went through
OptionalsourceLength: number
a record consumer that builds the image; attach it next to the address-space applier and the image is written in the same pass as the parse, whatever the source