Cluster mode

rcp copy -nodes w0,w1,w2 SOURCE DESTINATION spreads a copy over a worker fleet: the coordinator (this process) lists and plans as usual, then hands the file batches, balanced by size, to rcp copybatch workers started over ssh on each node and collects one result line per file. Directories, hard links, symlinks, metadata and the catalog stay with the coordinator, so resume -id and sync -id work on a fleet-made copy exactly as on a local one. A node needs rcp on its PATH and the same endpoints reachable: an export or a bucket is shared by nature, a local path has to be the same mount everywhere. localhost as a node name runs a worker on this host without ssh, and RCP_SSH names the ssh program. scan -nodes lists the top level here and one top-level subtree per worker, merging the entries. resume and sync take -nodes too.

-copybatch 'PROG ARGS' runs a program of yours instead of rcp copybatch on every node (or here, without -nodes), as a line protocol: the program gets SOURCE DESTINATION appended to its arguments, NUL-separated paths relative to the source on stdin, and prints one line per path, ok<TAB>PATH<TAB>BYTES<TAB>SHA256-or-empty<TAB>OWNER-REFUSED<TAB>XATTRS-REFUSED or fail<TAB>PATH<TAB>MESSAGE. A path with no line, or a worker that dies, is a failure for every file it was given; the coordinator never guesses.