fix(esh-pve): hardware watchdog, and close the single-resolver DNS SPOF

esh-pve hard-froze at 03:34 on 2026-08-19 and stayed frozen ~4.5 hours
until a manual power cycle. No panic, no OOM, no MCE — the journal stops
mid-operation. The whole ESH site lost DNS with it, because esh-userland
(VLAN 10, the PVC SSID and wired userland LAN) was handed exactly one
resolver: 10.0.50.45, AdGuard on esh-docker-vm, on a different VLAN, with
no secondary. Internet and routing were healthy throughout.

Two fixes.

1. DNS: 10.0.10.1 (the gateway, verified resolving) added as secondary on
   esh-userland via the UDM Classic API. Note this is degradation cover,
   not clean failover — clients that query resolvers in parallel will
   bypass AdGuard for a share of lookups.

2. Watchdog: softdog -> iTCO_wdt under systemd (RuntimeWatchdogSec=60),
   watchdog-mux masked. The box looked watchdog-protected and was not: a
   software watchdog cannot fire when the kernel it lives in is wedged,
   and watchdog-mux only pets the device while an HA client is connected,
   which never happens on a cluster with no HA resources. Firmware does
   not block the TCO timer here, checked before committing to it.

Also pins VM 102 off (onboot: 0). It starts with full GPU passthrough and
vfio-pci enabling that device is the last thing the kernel logged, 39
minutes before the freeze. The other suspect is the kernel itself: the
host ran 4.5 months on 6.8.12-16, took 6.8.12-42 in an apt batch on
08-18, and died 20 hours into the first boot on it. 6.8.12-16 is still
installed as the rollback.

The playbook is idempotent — a second run skips all six steps and passes
all six verifies. The watchdog is confirmed armed (identity=iTCO_wdt,
state=active, held by PID 1) but has NOT been observed firing; proving
that needs a deliberate wedge.

Memory also corrects two wrong mid-incident calls: the mgmt VLAN is
routed over the site tunnel and is not firewalled off — both symptoms
were the dead host generating ICMP unreachables.

persistent-memory.md

@@ -109,6 +109,8 @@ no longer deployed sidecars here. See Recent decisions.)
 
 ## Current state / in-flight
 
+- **🔴→🟢 ESH OUTAGE 2026-08-19 — esh-pve hard-froze 03:34, ~4.5h, whole house lost DNS.** Presented as "wifi/routing issues"; internet was healthy throughout. Cause: `esh-userland` (VLAN 10, the `PVC` SSID) handed out **one** resolver, `10.0.50.45` (AdGuard on `esh-docker-vm`) — cross-VLAN, no secondary — and its hypervisor died. **Recovered by hand power-cycle; all VMs, cluster quorum and DNS restored.** Two fixes landed: gateway `10.0.10.1` added as secondary DNS on esh-userland (operator-approved, first confirmed WRITE on the ESH UDM key), and **`softdog` → `iTCO_wdt` hardware watchdog owned by systemd** (`playbooks/esh-pve-hardware-watchdog.yaml`, idempotent, verified armed) so a repeat self-recovers in 60s. **VM 102 pinned off** (`onboot: 0`) as the passthrough suspect. **⏳ OPEN:** (a) the watchdog is armed but **has not been proven to fire** — needs a deliberate wedge to confirm; (b) AMT/vPro still unusable until an onboard **RJ45** is cabled (the MS-01 is SFP+-only on the network and AMT cannot ride it); (c) kernel `6.8.12-16` rollback held in reserve if it freezes again. → `persistent-memory.d/2026-08-19-esh-pve-freeze-dns-spof.md`
+
 _As of 2026-08-19 (late) — a long infra session, all of it landed and committed: **fleet `*.internal` DNS is live** (git-sourced, 42 names, three resolvers incl. a NEW colo one), **waterland studio containerised** on irv-ml1, **Homepage cleaned up and themed** with Australis Skyfall + an Arbo-generated background, and **four unmanaged stacks adopted** into `stacks/` (two of which turned out to be quietly broken — SearXNG's healthcheck, SeaFile down 3 months). ⚠ 17 commits unpushed. ~~⚠ 2 unread althing messages from waterland-dev left deliberately undrained~~ — **drained 2026-08-19 post-`/clear`; thread closed, see below.**_
 
 - **🟢 FLEET `.internal` DNS — LIVE 2026-08-19.** `<host>.<site>.internal`, sites `ana`/`esh`/`nh3`. `dns/internal.yaml` is the source of truth; `scripts/dns-sync.py` reconciles the three AdGuard resolvers (diff → prompt → apply, idempotent). 42 names resolving from all three sites. **Colo got its first resolver ever** (`stacks/adguard-ana/`, API on **8053** not 8080, no blocklists by design) — before this, ana-docker resolved straight against `1.1.1.1`. Auth = a dedicated `infra-ops` AdGuard user, password vaulted `nh3-dev/adguard-infra-ops-password`. **⏳ TWO OPEN, both operator's to schedule:** (a) colo hosts still point at `1.1.1.1` so they do not yet *use* the new resolver — repointing a site's DNS is a separate change; (b) the static-v6 convention (each server at its site's `/64` with low bits echoing the v4 octet, `esh-docker-vm` → `…::45`) is **proposed, not ruled on**. The `v6:` column is empty and correct — no fleet host has a global v6 address yet. → `persistent-memory.d/2026-08-19-fleet-internal-dns.md`
@@ -164,6 +166,8 @@ _As of 2026-08-19 (late) — a long infra session, all of it landed and committe
 
 ## Recent decisions
 
+- `[2026-08-19]` **A *software* watchdog is not watchdog protection — esh-pve froze for 4.5h holding one.** softdog cannot fire when the kernel it runs in is wedged, and Proxmox's `watchdog-mux` never arms without HA resources, so the box *looked* protected and wasn't. Moved to the PCH `iTCO_wdt` under systemd. Also: a single cross-VLAN DNS entry with no secondary turns any VM outage into a whole-site outage. → `persistent-memory.d/2026-08-19-esh-pve-freeze-dns-spof.md`
+
 - `[2026-08-19]` **Fleet `.internal` DNS built and live — git-sourced, agent-managed, three resolvers.** Zone-scoped authority (ESH's hand-made `esteban.net` rewrites survive); the colo had no resolver at all; v6 column empty on purpose because SLAAC addresses rotate. → `persistent-memory.d/2026-08-19-fleet-internal-dns.md`
 
 - `[2026-08-19]` **waterland studio containerised on irv-ml1 — three landmines, all measured.** cupy needs CUDA *headers* the host had by accident; `uv run` re-syncs and prunes cupy at RUNTIME; the A6000 is container-index 0, not the host's 1. → `persistent-memory.d/2026-08-19-waterland-studio-containerised.md`