Add DDR5 DIMM temperature monitoring with ntfy alerts

Monitors spd5118 sensors every 5 minutes and sends an ntfy
notification if any DIMM exceeds 55°C. Opt-in via
ntfy-alerts.dimmTempCheck.enable, enabled on s0.

common/ntfy/default.nix

@@ -5,6 +5,7 @@
     ./service-failure.nix
     ./ssh-login.nix
     ./zfs.nix
+    ./dimm-temp.nix
   ];
 
   options.ntfy-alerts = {

common/ntfy/dimm-temp.nix

@@ -0,0 +1,69 @@
+{ config, lib, pkgs, ... }:
+
+let
+  cfg = config.ntfy-alerts;
+  hasNtfy = config.thisMachine.hasRole."ntfy";
+
+  checkScript = pkgs.writeShellScript "dimm-temp-check" ''
+    PATH="${lib.makeBinPath [ pkgs.lm_sensors pkgs.gawk pkgs.coreutils pkgs.curl ]}"
+
+    threshold=55
+    hot=""
+
+    while IFS= read -r line; do
+      case "$line" in
+        spd5118-*)
+          chip="$line"
+          ;;
+        *temp1_input:*)
+          temp="''${line##*: }"
+          whole="''${temp%%.*}"
+          if [ "$whole" -ge "$threshold" ]; then
+            hot="$hot"$'\n'"  $chip: ''${temp}°C"
+          fi
+          ;;
+      esac
+    done < <(sensors -u 'spd5118-*' 2>/dev/null)
+
+    if [ -n "$hot" ]; then
+      message="DIMM temperature above ''${threshold}°C on ${config.networking.hostName}:$hot"
+
+      curl \
+        --fail --silent --show-error \
+        --max-time 30 --retry 3 \
+        -H "Authorization: Bearer $NTFY_TOKEN" \
+        -H "Title: High DIMM temperature on ${config.networking.hostName}" \
+        -H "Priority: high" \
+        -H "Tags: thermometer" \
+        -d "$message" \
+        "${cfg.serverUrl}/service-failures"
+
+      echo "$message" >&2
+    fi
+  '';
+in
+{
+  options.ntfy-alerts.dimmTempCheck.enable = lib.mkEnableOption "DDR5 DIMM temperature monitoring via spd5118";
+
+  config = lib.mkIf (cfg.dimmTempCheck.enable && hasNtfy) {
+    systemd.services.dimm-temp-check = {
+      description = "Check DDR5 DIMM temperatures and alert on overheating";
+      wants = [ "network-online.target" ];
+      after = [ "network-online.target" ];
+      serviceConfig = {
+        Type = "oneshot";
+        EnvironmentFile = "/run/agenix/ntfy-token";
+        ExecStart = checkScript;
+      };
+    };
+
+    systemd.timers.dimm-temp-check = {
+      description = "Periodic DDR5 DIMM temperature check";
+      wantedBy = [ "timers.target" ];
+      timerConfig = {
+        OnCalendar = "*:0/5";
+        Persistent = true;
+      };
+    };
+  };
+}

machines/storage/s0/default.nix

@@ -10,6 +10,7 @@
   networking.hostName = "s0";
 
   ntfy-alerts.ignoredUnits = [ "logrotate" ];
+  ntfy-alerts.dimmTempCheck.enable = true;
 
   # system.autoUpgrade.enable = true;