SIGINT, SIGTERM and SIGHUP were caught for the whole run, but only the
ssh and sftp children acted on them: the mnemonic prompt waited for
Enter, and an interrupted `age encrypt -o` put the encryption of the
cut-off input in place. Now they end the tool at once, except where a
command cleans up first: `ssh to` and `ssh install` while ssh or sftp
runs, and `age encrypt -o` and `age decrypt -o` while they write, where
a signal up to a tenth of a second after the input ends still removes
the unfinished file and exits 1. Those commands catch only the signals
the tool was not started ignoring, so a run under nohup survives a
hangup.
Model: opus-5-5
