Function mirror_append_to_global 

fn mirror_append_to_global(gfs: &Arc<FileStore>, zone: &str, data: &[u8])

Append data to the global transcript zone’s output file, creating it lazily on first write. Mirrors the per-channel write-through in handle_append_block_file; all errors are logged and swallowed so the hot stdout path is never blocked by the global store.