{
  pkgs,
  service_configs,
  config,
  inputs,
  lib,
  utils,
  ...
}:
let
  cfg = config.services.llama-cpp;
  modelUrl = "https://huggingface.co/bartowski/google_gemma-4-E2B-it-GGUF/resolve/main/google_gemma-4-E2B-it-IQ2_M.gguf";
  modelAlias = lib.removeSuffix ".gguf" (baseNameOf modelUrl);
in
{
  imports = [
    (lib.mkCaddyReverseProxy {
      subdomain = "llm";
      port = service_configs.ports.private.llama_cpp.port;
    })
  ];

  services.llama-cpp = {
    enable = true;
    model = toString (
      pkgs.fetchurl {
        url = modelUrl;
        sha256 = "17e869ac54d0e59faa884d5319fc55ad84cd866f50f0b3073fbb25accc875a23";
      }
    );
    port = service_configs.ports.private.llama_cpp.port;
    host = "0.0.0.0";
    package = lib.optimizePackage (
      inputs.llamacpp.packages.${pkgs.system}.vulkan.overrideAttrs (old: {
        patches = (old.patches or [ ]) ++ [
        ];
      })
    );
    extraFlags = [
      "-ngl"
      "999"
      "-c"
      "65536"
      "-ctk"
      "turbo3"
      "-ctv"
      "turbo3"
      "-fa"
      "on"
      "--api-key-file"
      config.age.secrets.llama-cpp-api-key.path
      "--metrics"
      "--alias"
      modelAlias
      "-b"
      "4096"
      "-ub"
      "4096"
      "--parallel"
      "2"
    ];
  };

  # have to do this in order to get vulkan to work
  systemd.services.llama-cpp.serviceConfig.DynamicUser = lib.mkForce false;

  # ANV driver's turbo3 shader compilation exceeds the default 8 MB thread stack.
  systemd.services.llama-cpp.serviceConfig.LimitSTACK = lib.mkForce "67108864"; # 64 MB soft+hard

  # llama-server tries to create ~/.cache; ProtectSystem=strict + impermanent
  # root make /root read-only. Give it a writable cache dir and point HOME there.
  systemd.services.llama-cpp.serviceConfig.CacheDirectory = "llama-cpp";
  systemd.services.llama-cpp.environment.HOME = "/var/cache/llama-cpp";

  # turbo3 KV cache quantization runs a 14-barrier WHT butterfly per 128-element
  # workgroup in SET_ROWS. With 4 concurrent slots and batch=4096, the combined
  # GPU dispatch can exceed the default i915 CCS engine preempt timeout (7.5s),
  # causing GPU HANG -> ErrorDeviceLost. Increase compute engine timeouts.
  # Note: batch<4096 is not viable -- GDN chunked mode needs a larger compute
  # buffer at smaller batch sizes, exceeding the A380's 6 GB VRAM.
  # '+' prefix runs as root regardless of service User=.
  systemd.services.llama-cpp.serviceConfig.ExecStartPre = [
    "+${pkgs.writeShellScript "set-gpu-compute-timeout" ''
      for f in /sys/class/drm/card*/engine/ccs*/preempt_timeout_ms; do
        [ -w "$f" ] && echo 30000 > "$f"
      done
      for f in /sys/class/drm/card*/engine/ccs*/heartbeat_interval_ms; do
        [ -w "$f" ] && echo 10000 > "$f"
      done
    ''}"
  ];

  # upstream module hardcodes --log-disable; override ExecStart to keep logs
  # so we can see prompt processing progress via journalctl
  systemd.services.llama-cpp.serviceConfig.ExecStart = lib.mkForce (
    "${cfg.package}/bin/llama-server"
    + " --host ${cfg.host}"
    + " --port ${toString cfg.port}"
    + " -m ${cfg.model}"
    + " ${utils.escapeSystemdExecArgs cfg.extraFlags}"
  );

}