hardware-health: rasdaemon MCE attribution + watchdog auto-reboot on mediaserver

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

common.nix

@@ -44,6 +44,7 @@
     ./services/memos.nix
     # ./services/neko.nix  # superseded by selkies.nix (Neko can't handle GW's mouse grab)
     ./services/selkies.nix
+    ./services/hardware-health.nix
   ];
 
   ### Make build time quicker

services/hardware-health.nix

@@ -0,0 +1,35 @@
+# services/hardware-health.nix — RAS error attribution + watchdog auto-recovery
+#
+# Context: Jun 2026 the dual Xeon E5-2697 v3 began throwing a storm of
+# *corrected* Machine Check Exceptions on both sockets (Bank 5 / Bank 20),
+# ~18k events in 36h, eventually hanging the box. Since this host is the
+# router, a hang takes the whole LAN offline until a manual power-cycle.
+#
+# This module:
+#   - rasdaemon: decodes every MCE to a specific DIMM/channel/socket and
+#     persists a per-component error DB, so a failing part can be named
+#     (needed for the seller's warranty claim). Query with `ras-mc-ctl
+#     --error-count` and `ras-mc-ctl --summary`.
+#   - hardware watchdog: if userspace hangs again, systemd stops petting
+#     /dev/watchdog0 and the chipset watchdog reboots the box (~30s),
+#     restoring the LAN without physical access.
+
+{ config, lib, pkgs, ... }:
+{
+  config = lib.mkIf (config.networking.hostName == "FredOS-Mediaserver") {
+
+    # Decode + log + persist machine-check / memory errors per component.
+    hardware.rasdaemon.enable = true;
+
+    # ras-mc-ctl on PATH for manual inspection.
+    environment.systemPackages = [ pkgs.rasdaemon ];
+
+    # Hardware watchdog: auto-reboot a hung box instead of a dead LAN.
+    # systemd pets /dev/watchdog0 at half the runtime interval; if it stops
+    # (hang), the chipset resets after RuntimeWatchdogSec.
+    systemd.settings.Manager = {
+      RuntimeWatchdogSec = "30s";
+      RebootWatchdogSec = "10min";
+    };
+  };
+}