First, if Jenkins runs as PID 1, then it's difficult to differentiate between process that were re-parented to Jenkins (which should be reaped), and processes that were spawned by Jenkins (which shouldn't, because there's other code that's already expecting to wait them).

SIGTSTP is like SIGSTOP except that it can be caught and handled.

SIGSTOP and SIGKILL are two signals that cannot be caught and handled by a process.

In any case signal handling in shells is one of the least reliable and portable aspects. You'll find behaviours vary greatly between shells and often between different versions of a same shell. Be prepared for some serious hair pulling and head scratching if you're going to try to do anything non-trivial.

Both kill with a job specifier and terminal signals send to the entire process group, so both the shell and sleep.

I am trying to understand how CTRL+C terminates a child but not a parent process. I see this behavior in some script shells like bash where you can start some long-running process and then terminate it by entering CTRL-C and the control returns to the shell. Could you explain how does it work and in particular why isn't the parent (shell) process terminated? Does the shell have to do some special handling of CTRL+C event and if yes what exactly does it do?

Quit the program by sending a different signal to both processes, e.g. SIGQUIT with Ctrl + \.

The CTRL-\ key sends a kill signal to the foreground job which, under normal circumstances, is guaranteed to terminate it. This signal cannot be captured by a process. However, this means the process cannot cleanup and is just summarily stopped. In some cases, a process can be stuck in a kernel wait state so this signal never reaches it. In that case, the process is unusable but cannot be killed.

You need a trap in loop.sh. Traps are cleared for every subshell started unless they are explicitly trap ''SIG ignored by the parent.

Personally, I prefer signalling an error for invalid values