Bug#1103522: openssh-client: ssh-agent socket created in an unpredictable path

> >> If your output looks the same as above, can you share the output of:
> >> 
> >>     systemctl --user status ssh-agent.socket ssh-agent.service
> >> 
> >> That would let me see what your local process supervisor believes is
> >> going on with this service.  
> >
> > ○ ssh-agent.socket - OpenSSH Agent socket
> >      Loaded: loaded (/usr/lib/systemd/user/ssh-agent.socket; enabled;
> > preset: enabled) Active: inactive (dead)
> >    Triggers: ● ssh-agent.service
> >        Docs: man:ssh-agent(1)
> >      Listen: /run/user/1000/openssh_agent (Stream)
> >
> > × ssh-agent.service - OpenSSH Agent
> >      Loaded: loaded (/usr/lib/systemd/user/ssh-agent.service; static)
> >      Active: failed (Result: exit-code) since Fri 2025-04-18 16:26:54 CEST;
> > 2 weeks 5 days ago Duration: 18min 13.762s
> >  Invocation: 9e8c3dc015d64454810ba837d4433547
> > TriggeredBy: ○ ssh-agent.socket
> >        Docs: man:ssh-agent(1)
> >    Main PID: 3932465 (code=exited, status=2)
> >    Mem peak: 1.9M
> >         CPU: 24ms  
> 
> OK, this is just telling me that you aren't using the systemd unit any
> more, right?

Here is what I did to disable my non-systemd-managed agent and run it again
through systemd:
killall ssh-agent
systemctl --enable ssh-agent.service ssh-agent.socket
systemctl --user start ssh-agent.service

Here is the new output of `systemctl --user status ssh-agent.socket
ssh-agent.service`:

○ ssh-agent.socket - OpenSSH Agent socket
     Loaded: loaded (/usr/lib/systemd/user/ssh-agent.socket; enabled; preset: enabled)
     Active: inactive (dead)
   Triggers: ● ssh-agent.service
       Docs: man:ssh-agent(1)
     Listen: /run/user/1000/openssh_agent (Stream)

● ssh-agent.service - OpenSSH Agent
     Loaded: loaded (/usr/lib/systemd/user/ssh-agent.service; static)
     Active: active (running) since Thu 2025-05-08 17:11:05 CEST; 2min 9s ago
 Invocation: 4f8408f214414c46b1b5c1bac906a5cf
TriggeredBy: ○ ssh-agent.socket
       Docs: man:ssh-agent(1)
   Main PID: 3227523 (ssh-agent)
      Tasks: 1 (limit: 21468)
     Memory: 1.1M (peak: 2M)
        CPU: 23ms
     CGroup: /user.slice/user-1000.slice/[email protected]/app.slice/ssh-agent.service
             └─3227523 /usr/bin/ssh-agent -D

> >> How are you restarting the ssh-agent user service?  
> >
> > I used to restart it with:
> > systemctl --user restart ssh-agent.service  
> 
> Under what circumstances would you need to do this?  I'm not saying it's
> wrong (it should be fine!), i'm just trying to replicate the
> circumstances you found yourself in.

I only run that command when the agent is not running for some reason, like
what looked like a failure following the upgrade we are discussing. (it was not
a real failure, it’s only that the socket was no longer found where I expected
it to be)

> > But since I got bitten by the behaviour I reported, I stopped using the
> > systemd unit and now start the agent directly from my user ~/.profile:
> >
> > # Start SSH agent
> > export SSH_AUTH_SOCK="${XDG_RUNTIME_DIR:-/run/user/$(id -u)}/openssh_agent"
> > if [ ! -e "$SSH_AUTH_SOCK" ]; then
> > 	ssh-agent -a "$SSH_AUTH_SOCK" >/dev/null
> > fi
> >
> > For debugging purposes, I can disable that temporarily and get back to the
> > systemd unit, maybe try to get more debug output from it.  
> 
> Yes, please do try to disable that and see what you can replicate.  that
> would be great!  I'm unable to trigger the problem you described
> directly myself with the information we have so far.

Following the actions I listed above (disabling my workaround, re-enabling and
starting the systemd user units), I once again ended up with the socket created
in an unexpected path:
/tmp/ssh-Qyd6hMtI8ivT/agent.3227523

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