unifying mcron and shepherd, service woes, improvements

[raingloom]

Just throwing this out there:
mcron is basically a very simple service manager, so, why not just move
all its timer functionality into shepherd (like systemd's timer units)
and then we can have a unified way to manage and debug services.

But also, shepherd debugging is kind of terrible too, at least on Guix,
so we (and if no one else gets on it that probably means I) should do
something about that.
For example, it's pretty nontrivial to figure out how to run a
service's command in isolation. So far I always had to find it in
/proc, which is not great. stracing a service that fails to start is
also rather tricky. The best I could come up with is to run strace in a
loop and pgrep for the PIDs I'm interested in. Same goes for GDB, which
was still bad in general last time I tried it.

Security could also be improved probably. Can we have an OCAP model?
I feel like I don't know enough to say, so this mail is meant more as a
conversation starter.

So, can we do better? What other issues are there with Shepherd? Are
they fundamental design problems or just plain old bugs?

Or is everyone else happy with the current design and it's just me who
can't use Shepherd properly? 😅