Read a file from the project drive

Reads the current version, or with sha256 that version (current or superseded: what a sealed report names). Works with every computer of the project asleep or deleted; nothing is woken. ETag is the sha256 (If-None-Match answers 304). One Range: bytes=start-end, bytes=start- or bytes=-length answers 206 with Content-Range and only those bytes (If-Range with the ETag keeps it to that version); a range that starts at or past the end answers 416 with Content-Range: bytes */<size>.