Function process_file_content 

pub fn process_file_content<ObjectID: FsVerityHashValue>(
    repo: &Arc<Repository<ObjectID>>,
    writer: &mut SplitStreamWriter<ObjectID>,
    stats: &mut ImportStats,
    ctx: &mut ImportContext,
    fd: OwnedFd,
    size: u64,
    name: &str,
    zerocopy: bool,
    inline_buf: &mut Vec<u8>,
) -> Result<()>

Store the content of one file fd into the splitstream, choosing inline vs external storage based on the file size.

For files at or below composefs::INLINE_CONTENT_MAX_V0 bytes the content is read into inline_buf and embedded directly in writer. Larger files are stored as external objects in repo and referenced by hash.