Backend had zero logging. Frontend logs were fine (logging.basicConfig
in app.py). Now both services write structured logs to systemd journal:
journalctl -u vm-bench -f # frontend (LXC)
journalctl -u vm-bench-backend -f # backend (srv2)
{job_id} in f-strings was interpreted as Python variable instead
of FastAPI path parameter. Double braces {{job_id}} produce
literal {job_id} in the route string.