setting open files limit for daemon processes

[Attila Lendvai]

dear Guix'ers,

"The per-process limit is inherited by each process from its parent", and 
Shepherd is the init process. when it spawns a daemon, it inherits its open 
files limit.

i have successfully set the limit for the daemon user using:

(pam-limits-service
  (list
    (pam-limits-entry "*" 'both 'nofile 100000)))

and it is applied as observable with:

su - [daemon user] -c 'ulimit -aHS' -s `which bash`

and yet, when i `herd stop` and `herd start` the process, even though it's 
running with the right uid, its limit is still the default, as per:

cat /proc/[pid]/limits

the suggested solution i find online is to edit:

/etc/pam.d/common-session-noninteractive

to include:

session required pam_limits.so

but this is not how Guix arranges things.

i looked into extending my service 
(https://github.com/attila-lendvai/guix-crypto/blob/main/src/guix-crypto/services/swarm.scm)
 to add some pam rules, but i'd need to learn a whole lot of pam for that, and 
the Guix code around service extensions is also rather complex, so i decided to 
ask here:

is there an example somewhere demonstrating how to increase the open file limit 
of a daemon process?

any hints/guidance is appreciated.

--
- attila
PGP: 5D5F 45C7 DFCD 0A39n