The catalog

One directory per copy ID, at -catalog DIR, else $RCP_CATALOG, else $XDG_STATE_HOME/rcp/catalog, else ~/.local/state/rcp/catalog. Inside, index.tsv starts with the two endpoints and then holds one tab-separated line per completed entry: path, kind, size, mtime (ns), mode, uid, gid, SHA-256, source inode (the column sync uses to recognize a renamed file; catalogs written without it still read). Lines are appended and flushed as entries complete, so a copy killed part-way leaves a truthful index. A copy ID that already exists is refused: two copies must never share a resume record. jobs.log beside the catalogs records every command.