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 `ssh to` and `ssh install` catch them from
once the mnemonic is read until their cleanup has run, and everywhere
else they end the tool at once, except while `age encrypt -o` or
`age decrypt -o` writes. There the work runs in the background, and a
signal that comes before it ends, or within a tenth of a second after,
removes the unfinished file and ends the tool with status 1, since
Ctrl-C on a pipeline can end the input just before the signal arrives.
Model: opus-5-5
