Function loose_form 

pub fn loose_form(kind: Kind, content: &[u8]) -> Vec<u8> 

The stored preimage of a git object: git’s loose-object form — <type> <len>\0 + content, the header inside the value (alkblobs ADR-018; the digest over exactly these bytes is git’s oid). The odb layer owns this composition — ObjectFront::put puts it, the read legs parse the header back out through gix_object::decode::loose_header.