Function read_upload_files 

pub(crate) fn read_upload_files(
    workspace: &Path,
    checked: &[String],
) -> Result<Vec<UploadFile>, String>

Read the files check_upload_paths approved. Each is opened once, and the check is repeated on the open handle: the file it really refers to must be a regular file inside the workspace. The bytes are read from that same handle and the page is given the bytes, never a path, so replacing a checked file with a link afterwards changes nothing.