The first sftp connection now lists ~/.ssh before it fetches
authorized_keys. The file reads as empty in just two cases: sftp reports
~/.ssh itself as not there, or the listing succeeds and the fetch then
reports the file as not there. A directory that is there but cannot be
entered, or a file that cannot be read, fails the run and writes nothing,
so a ~/.ssh whose mode shuts the user out is no longer read as a host
with no file and replaced by one holding the new key alone. The write
connection makes ~/.ssh and sets 0700 only when the read found none; an
existing directory keeps its mode.
Model: opus-4-8
ssh install no longer runs a command on the host. It reads .ssh/authorized_keys over sftp, takes the empty reading only from sftp's own message about that path, appends the derived key locally when it is not already present, uploads the result beside the file with mode 0600 and renames it over the original. Any other failure prints what sftp said, writes nothing and exits 1. sftp batch mode disables password prompts, so a key or agent is required; a directory the owner cannot enter reads as a host with no file, which README.md states.
Model: opus-5 (implementation); fable-5-1 (landing)
keyfunc ssh install appends the public line on a host through the system ssh, only when absent, feeding the line on standard input; keyfunc ssh to serves the derived key from an in-process agent on a private socket and runs the system ssh with it, the private key never on disk. Two review rounds; the second passed with no findings.
Model: opus-5 (implementation and review); fable-5-1 (landing)