The dashboard LOAD tab always showed "no running agent containers":
container_stats::gather() looked for each agent's cgroup at
machine.slice/machine-h\x2d<name>.scope, but that path never exists.
nixos-container runs `systemd-nspawn --keep-unit` with
`Slice = "machine.slice"` (nixpkgs virtualisation/nixos-containers.nix),
so --keep-unit means no separate machined `machine-<name>.scope` is
created — the container's cgroup IS the launching service unit,
`container@<machine>.service`, under machine.slice. systemd-machined
still logs "New machine <name>" (registration), which is what made the
scope-path assumption look plausible, but the cgroup stays on the unit.
Fix scope_dir to machine.slice/container@<machine>.service and drop the
\x2d escaping (the service unit name is used verbatim in the cgroup dir;
the journal shows the literal `container@h-<agent>.service`). Adds a unit
test pinning the path.
Per review: available_parallelism() respects the hive-core process's
CPU affinity, so if it's ever affinity-pinned the denominator would
under-count and inflate cpu_pct. Read the online host CPUs from
/sys/devices/system/cpu/online instead (fall back to the process count,
then 1) so the 'percent of total host CPU' definition holds regardless.
C0NT41N3R L04D on the SYST3M tab + GET /api/container-resources.
Backend (hive-c0re/src/container_stats.rs): reads cgroup v2 cpu.stat +
memory.{current,peak,max} for each running agent machine
(machine-h\x2d<name>.scope under machine.slice), read-only/world-
readable so no hive-priv. CPU is a two-sample (~200ms) host-normalised
percentage; one shared sleep covers all agents. Skips agents whose
scope dir is absent (= not running). Network omitted: agents share the
host netns, no per-container counter.
Frontend: a polled C0NT41N3R L04D table on SYST3M (agent / cpu / mem /
peak / limit with meter bars), reusing the ST4TS table style. Polls
/api/container-resources every 5s only while the tab is active.
Backend reviewed-in-principle by damocles (path escaping + cpu delta
math); ping for the on-host sign-off.
