> unless the parent does implement such propagation

or if the signal is send to 0, or -PGID or if signal target PID is a group leader / session id or any other subtleties

But you're right the general case is that children won't be interrupted.

Right. Perhaps welder is confused by the behaviour of process groups and controlling terminals.

Yep, my bad. I forgot it's only because systemd defaults to control-group.