{
  pkgs,
  lib,
  ...
}:
let
  # Composite GPU id used by lactd: <pci_id>-<subsys_id>-<slot>.
  # ASRock RX 7800 XT (Navi 32). Verify with `lact cli list-gpus` if the
  # PCI slot ever changes (e.g. after adding/removing PCIe devices).
  gpuId = "1002:747E-1849:5326-0000:0a:00.0";
in
{
  # LACT (Linux AMDGPU Configuration Tool): https://github.com/ilya-zlobintsev/LACT
  # Config schema reference: <lact src>/docs/CONFIG.md.
  # /etc/lact/config.yaml is a read-only symlink to /nix/store, so GUI "Apply"
  # fails — settings are Nix-only. lactd auto-restarts on config change via the
  # upstream module's restartTriggers.
  services.lact = {
    enable = true;
    settings = {
      # Pin to current Config schema; bump in lockstep with lact upgrades to
      # avoid a v(N)→v(N+1) migration save() failing against the RO symlink.
      version = 5;
      daemon = {
        log_level = "info";
        admin_group = "wheel";
      };
      apply_settings_timer = 5;
      gpus.${gpuId} = {
        # ASRock RX 7800 XT (Navi 32). Voltage offset tuned via sweep with
        # clpeak under perf=high (sustained DPM7); visible artifacting on the
        # display engine appeared at -300 mV, so this sits 75 mV below that
        # cliff for a real-world safety margin (cool clpeak < hot gaming).
        voltage_offset = -130; # mV; kernel range on this card: -450..0
        max_core_clock = 2400; # MHz; default boost ~2520
        power_cap = 200.0; # W; default 220, max 280
        performance_level = "auto";
      };
    };
  };

  # Keep the existing pre-start sleep that lets amdgpu sysfs settle before
  # lactd probes it. Purely additive — the upstream module sets no ExecStartPre.
  systemd.services.lactd.serviceConfig.ExecStartPre = "${lib.getExe pkgs.bash} -c \"sleep 3s\"";
}