Signals end every command, not only ssh to and ssh install (closes #48)

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

README.md

@@ -288,6 +288,18 @@ girl mad pet galaxy egg matter matrix prison refuse sense ordinary nose
 Errors go to standard error and the exit status is 1, except for `ssh to`, which
 passes through `ssh`'s own exit status.
 
+SIGINT, SIGTERM and SIGHUP end any command at once, at the mnemonic prompt too,
+with the status a shell gives a program killed by that signal (130 for SIGINT).
+An interrupted `age encrypt -o` or `age decrypt -o` leaves no file. While it is
+writing the file, the signal makes it remove the unfinished file, leave a file
+already at the named path as it was, and exit with status 1. It puts the file in
+place a tenth of a second after its input ends, and a signal in that time still
+counts: Ctrl-C on a pipeline also ends the program feeding it, so the input can
+end just before the signal arrives. While `ssh to` or `ssh install` has `ssh` or
+`sftp` running, the signal ends that program instead, the tool removes its agent
+socket or working files, and it exits with status 1, or for `ssh to` with
+`ssh`'s own status if `ssh` reported one.
+
 ## Entrypoints
 
 The repo adheres to the