3 0 Opens, advances, completes, or aborts one bounded Kaptan virtual-file transfer. Requested or next accepted byte position. Exact complete file size advertised when the transfer is opened. CRC-32C of the complete file. Client-selected nonzero transfer identity retained for the complete transfer and not reused by that source during the ten-second replay lease. Requests use UNSPECIFIED; responses carry the authoritative outcome. Logical bytes initialized in content. Canonical path for open requests or bounded outcome detail in responses.