Monitor teardown SIGHUPed and SIGKILLed every remembered child group
when the transport closed. sshd signals nothing at a non-PTY session
end; background jobs with redirected stdio survive and reparent to
init. Clients rely on that: VS Code Remote-SSH starts its remote
server as a plain background job in the session's group and expects
it to outlive connection drops, and tailscale upgrades run as
non-PTY execs whose work should survive a daemon restart.
Now only SSHTerminationError causes (revocation, session-duration,
recording failure) kill the process tree. Everything else — client
disconnect, daemon shutdown — closes I/O without signals: PTY masters
close and the driver SIGHUPs the foreground group, non-PTY processes
exit on EOF and SIGPIPE or keep running. Monitor teardown kills only
forwarding children, unless revocation armed the new kill-all op
first, since its per-session kicks race the close. No zombie leak:
the monitor reaps its table, and reparented survivors are reaped by
init.
Fixes#22076
Signed-off-by: James Tucker <james@tailscale.com>
Change-Id: I70b4ef40035330dd542d256ba79d889a12426a74
James Tucker
9e396012a8