robustness: hardware watchdog + hbc heartbeat client

Two TODO Tier-1 items:

- Hardware watchdog: power/10-vanlink-watchdog.conf drop-in sets
  RuntimeWatchdogSec=20s + RebootWatchdogSec=5min; deploy.sh applies it via
  daemon-reexec. PID1 pets intel_oc_wdt; a >20s systemd hang hard-resets the box.

- Heartbeat / dead-man's switch: vendored hbc.yaml + hbc.service report to
  hbd.wrede.pvt (UDP 50003) every 15s as user andreas, shipping cpu/mem/disk/
  network/zfs metrics. The hbc binary is installed once via the heartbeat
  project's installer (README §4); deploy.sh starts the service when present.

Auto-power-on-when-mains-returns: documented as a BIOS-only option (not
OS-controllable on this ZenBook) in README §3 + TODO, per decision.

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

TODO.md

@@ -20,17 +20,19 @@ value-for-effort. Generated 2026-06-29 from a robustness review of the live box.
 
 ## Tier 1 — high value, pieces already on hand
 
-- [ ] **systemd hardware watchdog** — `/dev/watchdog` exists but isn't wired. A hung
-  kernel/driver currently needs someone to open the lid. Given the EC-latch and
-  USB-hub-hang history, auto-reboot-on-hang is the biggest unattended win.
-  Set `RuntimeWatchdogSec` (and `RebootWatchdogSec`) in `/etc/systemd/system.conf`.
-- [ ] **Auto power-on when mains returns** — the 10% auto-shutdown is currently a
-  one-way trip; a laptop won't boot itself when solar/shore power returns. Needs the
-  BIOS "restore on AC loss → power on" setting (cannot be set from the OS). Without
-  it the safe-shutdown can strand the router. **Manual BIOS toggle.**
-- [ ] **Heartbeat / dead-man's switch** — every existing alert can only fire if the box
-  is alive. A periodic ping to healthchecks.io (or similar) inverts it: silence =
-  something is dead (panic, no-boot, total power loss).
+- [x] **systemd hardware watchdog** — DONE. `power/10-vanlink-watchdog.conf` drop-in sets
+  `RuntimeWatchdogSec=20s` + `RebootWatchdogSec=5min`; PID1 pets `intel_oc_wdt`, chip
+  hard-resets the box if systemd hangs >20s. Deployed via `daemon-reexec`.
+- [x] **Auto power-on when mains returns** — RESOLVED as "document only". Not
+  OS-controllable on this ZenBook: `/proc/acpi/wakeup` is wake-from-suspend (S3/S4) only,
+  and "restore on AC loss" is a BIOS/firmware feature this laptop likely doesn't expose.
+  The 10% auto-shutdown is therefore a one-way trip until manual power-on. **Action:**
+  check BIOS setup for an "AC power-on / restore on AC loss" option and enable it if
+  present (documented in README §3, Battery monitor).
+- [x] **Heartbeat / dead-man's switch** — DONE. `hbc` (heartbeat client, from
+  git.wrede.ca/andreas/heartbeat) installed to `~/venvs/hbd` + `~/bin/hbc`; `hbc.service`
+  reports to **hbd.wrede.pvt** (UDP 50003) every 15s as user `andreas`, shipping cpu/mem/
+  disk/network/zfs metrics. Config `/etc/hbc.yaml`, vendored in `heartbeat/`.
 - [ ] **Connectivity alerts → Pushover** — `van-failover` already knows when it fails
   over or when ALL WANs are down; it just logs it. Pipe those events to the Pushover
   plumbing so internet loss is alerted, not just battery.