Plenary.job:shutdown(code, signal) not terminating process

Reproduce the report using the mentioned config.lua setup, plenary.job, and strace, then inspect the Job:shutdown entry point and its process-handling behavior. Compare shutdown with vim.loop.kill and verify that the requested signal reaches the started process and that on_exit reports the resulting termination.

Maybe I'm not understanding the concept of Job or shutdown, but I expect the started process to finish when I shutdown the job with the shutdown function (or at least send the signal given as parameter), but it's not doing either for some processes.

I have set up a simple configuration to reproduce this issue

1. Create the following file, config.lua

--- use your own way to load plugins
vim.fn['plug#begin']('~/.vim/plugged')
  vim.fn["plug#"]('nvim-lua/plenary.nvim')
vim.fn['plug#end']()


--- @type Job
local Job = require("plenary.job")

MyJob = Job:new({
        command = "mycommand.sh",
        on_exit = vim.schedule_wrap(function(self, code, signal)
          print(string.format("PID: %d | code: %d | signal: %d", self.pid, code, signal))
        end),
      })

MyJob:start()

2. Start neovim with neovim -u config.lua
3. Get the process PID with :lua print(MyJob.pid)
4. Watch the process system calls with sudo strace -p <pid> where is the pid obtained in the previous step.
5. Shutdown the process in neovim with :lua MyJob:shutdown(0, 3). I expect the process to receive a SIGQUIT(3) signal but nothing appears in the strace output. It doesn't matter if you run shutdown without arguments or with another signals, still no output in strace. However, shutdown executes on_exit correctly and prints the following PID: <pid> | code: 0 | signal: 3.
6. To verify that strace should output something when it receives a signal, run kill -n 3 <pid>
   
   Alternatively, you could also use :lua vim.loop.kill(MyJob.pid, 3)

Am I doing something wrong? What should I use in order to stop the process instead?

Just for some context, this is where I'm trying to use it, right now using vim.loop.kill as a workaround (in that code I'm killing a process started by the job instead), but I'm expecting the following to work

function M.stop()
  if job then
    job:shutdown() -- or maybe use a signal to terminate the process
end

I'm getting the following behaviour instead: (almost a copy of this comment in a PR for flutter-tools.nvim
Execute a command to start the job: (The first one is the job, second one the child process)

Both processes are in the process tree, bash and dart (the parent of zsh is my terminal)

Executing the stop lua function inside neovim executes the on_exit function, but the processes are still there (both of them actually, same tree)

After exiting the processes, instead of terminating, are detached and moved to the root (systemd):