Function mirror_append_to_global 

pub(super) fn mirror_append_to_global(
    gfs: &Arc<FileStore>,
    zone: &str,
    data: &[u8],
) -> Option<AppendPos>

Append data to the global transcript zone’s output file, creating it lazily on first write, and return where it landed. Mirrors the per-channel write-through in handle_append_block_file; all errors are logged and swallowed (None) so the hot stdout path is never blocked by the global store.