ssh to and ssh install started the system ssh and sftp with the tool's
whole environment, so a mnemonic taken from KEYFUNC_MNEMONIC stayed in
the child's environment for as long as it ran, readable by the same user
and forwardable to the host through a SendEnv line. ssh to keeps the
private key inside the tool; the mnemonic must not leave it either.
A shared helper in the ssh cli package hands both children the tool's
environment with KEYFUNC_MNEMONIC and KEYFUNC_MNEMONIC_COMMAND removed.
The mnemonic command itself still runs with the full environment. The
stand-in ssh and sftp in the tests now record their environment, and two
tests show neither variable reaches them while another one does.
Model: opus-4-8
sneak