# REPORT — TASK-D Part 3: the guest-network watchdog (R-54) · felhom-agent v0.91.2 → **v0.92.1**

**Date:** 2026-07-21 · Trunk, pushed to `main`. **Baseline:** `08b55a1` (clean, == `origin/main`).
**Deployed, running on felhom-pve, and STOP-2 RAN — the incident was replayed and the watchdog
prevented it (§6b).** Every claim below was observed.

---

## 1. What this closes

`INCIDENT-guest-dhclient-killed-2026-07-20.md` §5, "OPEN RISK": **the guest's DHCP client is
unsupervised.** ifupdown starts it once at boot and nothing restarts it. When it was killed on
2026-07-20 the guest kept working for another **~80 minutes** on its unexpired lease; only at expiry
did the address and default route vanish, taking the Cloudflare tunnel, hub reports, catalog sync
and the controller→agent channel with them — a 1h15m outage in which every observable signal said
healthy for the first 80 minutes.

**So the design consequence is the whole feature: liveness of the DHCP client is itself a probe.**
The watchdog flags a DHCP guest unhealthy on `pgrep -x dhclient` alone, while the address and route
are still perfectly present. Waiting for the IP to disappear is waiting out exactly that silent
window — and the red-proof reproduces it (§5).

Host tier is not a preference: a guest with no default route cannot repair its own default route.

---

## 2. Shipped

`internal/guestnet` (probe.go / watchdog.go / report.go), built on the wg-tunnel + storage watchdog
loop shape, started with `go wd.Watch(ctx)` like `selfheal`.

- **Four fixed-shape `pct exec` probes**, all constant argv + the numeric vmid: address, default
  route, `/etc/network/interfaces` mode, `pgrep -x dhclient`. No shell anywhere; no guest-supplied
  data is ever interpolated into a command.
- **Heal = the incident's restored invocation, verbatim**, logged at INFO before it runs:
  `pct exec <vmid> -- dhclient -pf /run/dhclient.eth0.pid -lf /var/lib/dhcp/dhclient.eth0.leases eth0`
  A test pins that argv element by element.
- **Dampers** (this runs a privileged command inside a customer's container, so it is built to
  under-act): two CONSECUTIVE bad probes before any heal, ≥10 min between heals per guest, ≤3
  heals/hour, and observe-only while the guest — or the agent itself — has been up under 3 minutes.
- **Refuses to act** on: a static guest (dhclient must never fight a static config; a static guest
  missing its address is reported loudly and left to **R-50**), an unknown interface mode, a guest
  it cannot probe, and an ownership-unproven guest list. The guest source is the pool-verified
  `ListLXC` ∩ felhom-pool (audit A1) — never a bare `ListLXC`, which under a broad token would run
  dhclient inside a co-tenant's container.
- **A failed PROBE is never a dead client.** `pgrep` exits 1 with EMPTY stderr on no-match; anything
  on stderr means the probe itself failed → `unknown`. Without that rule a missing `pgrep` would
  heal forever.
- **Healthy cycles log a Debug line.** v0.91.2's lesson, one day old: if the quiet path is silent,
  "no alarms" and "never probed" are the same evidence.
- **Not in the `errc` fan-out** — a watchdog over customer guests must never be able to terminate
  the agent. A test asserts that, because joining the fan-out would also make the shutdown drain
  bound off by one.
- **Report block:** `GuestNetStatus` on `HostReport` (`guest_net`, omitempty), additive and stored
  opaquely hub-side like `pbs_dr` / `wireguard`. **No hub code was touched.**

**Two deliberate deviations from TASK-D, both stated up front:**

1. **`GuestNetStatus`, not `WireGuestNet`.** In this repo `Wire*` is the DOWN direction
   (`WireDesiredState` / `WirePBSDR` — what the hub sends the agent); UP-direction report stanzas
   are `*Status`. `WireGuestNet` on `HostReport` would have been the only report block named against
   the convention.
2. **A sudoers change was required** — see §4. The brief said none was needed.

**Config `guest_net` is this repo's first default-ON gate.** Every other gate defaults to false
because those features reach outward (an offsite endpoint, an OOB tunnel) and enrolling a box by an
update would be wrong. This one looks only inward at guests the agent already owns, and the failure
it prevents exists on every box today. A watchdog that must be remembered per box is a watchdog
that is missing on the box that needed it. Opt-out is explicit: `"guest_net": {"disable": true}`.

---

## 3. Phase-0 probes

**P3 (watchdog ground truth) — DONE 2026-07-21, live from guest 9201.** These exact bytes are the
parser fixtures, including the literal backslash `ip -o` emits and the trailing space on the route:

```
ip -4 -o addr show dev eth0 → 2: eth0    inet 192.168.0.104/24 brd 192.168.0.255 scope global dynamic eth0\       valid_lft 4916sec preferred_lft 4916sec
ip route show default       → default via 192.168.0.1 dev eth0
pgrep -x dhclient           → 235839                       (rc=0; rc=1 + EMPTY stderr when absent)
ps -o args= -C dhclient     → dhclient -pf /run/dhclient.eth0.pid -lf /var/lib/dhcp/dhclient.eth0.leases eth0
/etc/network/interfaces     → iface eth0 inet dhcp
pct exec <bad vmid>         → rc=2, stderr "Configuration file 'nodes/demo-felhom/lxc/9999.conf' does not exist"
```

The live `ps` line confirms the running client's argv is byte-identical to the incident's restored
invocation — i.e. the heal reproduces the guest's own boot-time command, not an approximation.
A docker-bridge-only route table is also pinned as a negative (`172.17.0.0/16 dev docker0 …` must
never read as a default route — those were the exact leftovers in the incident).

**P4 (config surface + report pattern + loop precedent) — DONE** by reading the tree; the wg loop's
interval/damping/logging shape and the `pbs_dr` stanza's collector-seam pattern are what this copies.

---

## 4. The live finding: three of four probes had no sudoers grant

The agent runs non-root; `Privileged.Mode=sudo` fails closed with no prompt. The **first sweep after
deploying v0.92.0** logged:

```
level=WARN msg="guestnet: guest network not actionable — reporting only" vmid=9201
  state=unknown mode=unknown has_ip=true has_route=false
  detail="dhclient liveness probe failed: sudo: a password is required"
```

The watchdog behaved exactly as designed — it reported `unknown` and healed nothing rather than
acting blind — but it was blind. The existing allowlist granted only lanresolver's address read
(`pct exec [0-9]* -- ip -4 -o addr show dev eth0`), which is why `has_ip=true` while route, mode and
liveness all failed.

Fixed in **v0.92.1**: a `FELHOM_GUESTNET` alias with four fixed vectors (route, interfaces, pgrep,
heal). Every argument after the numeric vmid is a literal, so nothing the guest or the hub says can
widen the grant. The address read is **not** duplicated — it stays FELHOM_DNSMASQ's; one command,
one grant.

Plus **four `guestnet-*` capability rows**, so a host that has not taken the new sudoers file is
VISIBLE as degraded instead of silently watchdog-less. Deliberately **non-critical**: a missing
grant must not page an operator for every box on rollout day (the R-50b amber-fleet lesson).

**v0.92.0 is superseded, not overwritten — do not vouch it.** It was published before this was
found, so its binary lacks the capability rows and its release lacks the sudoers file. A published
version stays immutable (the v0.91.0 → v0.91.1 precedent).

---

## 5. Tests and red-proofs

Green gate: `go build ./... && go vet ./... && go test ./...` — all packages ok **except the known
flake** `TestGenerateRecoveryCode_EntropyAndFormat` (`internal/escrow`), which fails when the
wordlist yields a hyphenated word (`drop-down` → 11 tokens instead of 10). Confirmed pre-existing:
`internal/escrow` has not been touched since v0.88.0 and this task changes nothing there; observed
3/8 runs, consistent with the documented ~1/5.

New: `internal/guestnet/watchdog_test.go` (16 cases), `internal/hub/collect_guestnet_test.go` (2),
`cmd/felhom-agent/guestnet_wiring_test.go` (2).

| # | Red-proof | Mutation | Result |
|---|---|---|---|
| E | detect on process liveness, not address presence | `classify`'s DHCP arm reverted to IP-presence-only | **FAIL ×5.** The decisive one: `classify = "healthy", want "unhealthy"` for the July-20 fixture, `detail="address, default route and dhclient all present"`, and `heal ran 0 times`. That is the 80-minute silent window, reproduced exactly. Restored, green. |
| W | the watchdog must be wired | `SetGuestNetReporter` and `go gnWatchdog.Watch(ctx)` both commented out | **FAIL** with both reasons named — *"the guest_net stanza would never reach the hub (the exact v0.91.0 inert-seam defect)"* and *"it would be constructed, reported on, and never probe anything"*. Restored, green. |

**Every damper is asserted as an exact count, and the load-bearing assertions are the negatives** —
a static guest, an unprobeable guest, a boot-race guest (young guest AND young agent), a failed
probe tool and an ownership-unproven guest list must each record **zero** heal calls. The ceilings
are driven by an injected clock over a scripted **10 hours** of permanent failure: ≤30 heals total,
and never a second heal inside the 10-minute cool-off.

**Seam discipline (§9 rule 6)** — three production-path tests: the `guest_net` stanza is asserted
through the real `Collect` (and asserted ABSENT from the wire when no reporter is wired, so "not
wired" and "found nothing" can never look identical); and the `main.go` wiring is an AST walk for
the construction, the reporter call and the started goroutine. The AST form is deliberate — a
`strings.Contains` version of the twin test in felhom-controller **passed its own red-proof**,
because a commented-out call still contains the string.

---

## 6. Live validation (method: journald + capability self-check on felhom-pve)

| Step | Evidence |
|---|---|
| Publish 0.92.0 | `AGENT_SHA256=b1302790d412d22e969936ff52e3ee33e3edc111b8426364a21cdb1c5127ca6a`, round-trip GET verified — **superseded, do not vouch** |
| Publish 0.92.1 | `AGENT_SHA256=7424bc1c3c533eff9157e15a18d4635c624931f5a479a48126de77a94e6a3d4d`, round-trip GET verified |
| Deploy | `visudo -c` parsed OK → sudoers installed 0440 root:root (backup `/root/felhom-agent.sudoers.bak-preR54`) + binary installed (backup `felhom-agent.bak-0.91.2-preR54`) → `felhom-agent --version` = **0.92.1**, service `active` |
| Capability self-check | **`ok=68 total=68 degraded=0 inactive=0`** (was 64/64 before the four `guestnet-*` rows) — the sudoers grant is proven from the agent's own side, not assumed |
| Watchdog start | `INFO guestnet: watchdog starting interval=1m0s min_heal_interval=10m0s max_heals_per_hour=3 settle=3m0s` |
| **Healthy cycle** | **`level=DEBUG msg="guestnet: guest network healthy" vmid=9201 mode=dhcp has_route=true dhclient_alive=true`** (12:34:15 CEST) |
| Default-ON proven | `/etc/felhom-agent/agent.json` has **no** `guest_net` key at all — the watchdog runs on defaults, which is the whole point of the inverted gate |

**Note for the operator:** `log_level` on felhom-pve was temporarily raised to `debug` to capture
that Debug line (backup at `/root/agent.json.bak-debuglevel`). It is **still `debug`**, deliberately,
so STOP-2's heal chain is visible in journald. **Revert it to `info` after STOP-2.**

---

## 6b. STOP-2 — the incident replay (operator-present, 2026-07-21)

The 2026-07-20 kill, repeated deliberately. **The `/proc/<pid>/cgroup` check the incident produced
was applied before the kill** — the script refuses unless the pid's cgroup is guest 9201's, which is
the rule that would have prevented the original outage:

```
GATE OK — pid 336708 belongs to guest 9201 (0::/lxc/9201/ns/.lxc)
KILL at 2026-07-21T10:43:18Z / 12:43:18 CEST
after kill: no dhclient running; address 192.168.0.104/24 STILL PRESENT (valid_lft 4998s); default route STILL PRESENT
```

That second line is the whole point: the box looked perfectly healthy, with ~83 minutes of lease
left before any symptom would appear.

| Time (CEST) | Event |
|---|---|
| 12:43:15 | `DEBUG guest network healthy … dhclient_alive=true` — last good cycle |
| 12:43:18 | **kill -9** |
| **12:44:15** | **detected in 57 s, on process liveness alone** — `unhealthy (first bad probe — not acting yet) bad_probes=1 required=2`, detail *"dhclient is not running — the lease will not be renewed (the 2026-07-20 failure mode; address still present, renewal already dead)"* |
| 12:45:15 | second consecutive bad probe → `healing`, then `running heal command … cmd="pct exec 9201 -- dhclient -pf /run/dhclient.eth0.pid -lf /var/lib/dhcp/dhclient.eth0.leases eth0"` |
| **12:45:18** | **`guest network healed` ip=192.168.0.104 has_route=true dhclient_alive=true heals_last_hour=1** |

**Healed 120 seconds after the kill — roughly 80 minutes before the outage would have begun.** The
strongest evidence is therefore what did *not* happen, verified from inside the guest:

| Check | Result |
|---|---|
| `cloudflared` | **`Up 29 hours`** — the tunnel never dropped, never reconnected |
| DNS `gitea.dooplex.hu` | OK |
| hub | **302 in 0.16 s** |
| `https://felhom.demo-felhom.eu/` | **302 in 0.25 s** |
| new dhclient | pid 2043719, `cgroup=0::/lxc/9201/ns/.lxc`, argv byte-identical to the original |

On 2026-07-20 every one of those was dead for 1h15m. This time the outage was **prevented**, not
detected.

**The negative leg — 30 healthy minutes, run in full.** From the heal at 12:45:18 to 13:16:15:
**30 healthy Debug cycles** (exactly one per minute — the cadence is precise), **0 heals**,
**0 WARN**, **0 ERROR**. So the damper is not a mute and the quiet path is not silence: "no alarms"
stayed continuously distinguishable from "not probing", which is the v0.91.2 lesson holding in
production.

**An unplanned damper proof, against a REAL transient.** STOP-1's guest reboot at 12:53 caught the
guest mid-boot:

```
12:53:16 INFO  guest network unhealthy (first bad probe — not acting yet) detail="no IPv4 address on eth0" bad_probes=1
12:54:15 DEBUG guest network healthy …
12:54:15 INFO  guest network recovered previous_state=unhealthy
```

One bad probe, **no action**, then recovery. The two-consecutive-probes rule and the boot-race guard
did exactly what they exist for — a booting guest was not injected with a dhclient — and this was a
genuine transient, not a scripted one.

## 6c. The stanza ON THE WIRE — confirmed hub-side after STOP-3

Initially unverifiable here: `--selftest=hub` builds its own one-shot collector and never wires the
guestnet reporter, so it would have printed a misleading absence — worse evidence than none. (That
divergence between the selftest collector and the daemon's is worth a small fix; the same caveat is
already commented in the code for the pbs reporter.)

Closed instead by a **read-only** query of the hub's own store (`kubectl cp` of `/data/hub.db`,
opened `mode=ro`, copy deleted afterwards). The `guest_net` stanza is present, complete, and
round-trips every field:

```json
"guest_net": { "checked_at": "2026-07-21T11:32:10Z", "guests": [
  { "vmid": 9201, "state": "healthy", "mode": "dhcp", "ip": "192.168.0.104",
    "has_route": true, "dhclient_alive": true, "checked_at": "2026-07-21T11:31:07Z",
    "message": "address, default route and dhclient all present" } ] }
```

And the report history tells the whole story of this session from the hub's side:

| received (UTC) | agent | state | evidence |
|---|---|---|---|
| 10:30:27 | **0.92.0** | **`unknown`** | the sudoers-blind window — reported honestly as unknown, never as a false healthy and never as a false dead. The fail-safe is visible fleet-side, and this is independent confirmation that 0.92.0 was genuinely blind (so superseding it was right) |
| 10:48:12 | 0.92.1 | `healthy` | **`last_heal_at=2026-07-21T10:45:12Z`, `heals_last_hour=1`** — the STOP-2 heal, surfaced to the hub |
| 10:49:14 / 11:04:14 | 0.92.1 | `healthy` | same heal stamp, counter still 1 |
| 11:32:10 | 0.92.1 | `healthy` | heal history absent — see the limitation below |

**A limitation this surfaced, worth stating plainly: the damping state is in-memory only.** The
counters vanished from the 11:32 report because the agent was restarted at 11:17Z (the `log_level`
revert), which resets `heals`/`lastHealAt`. So the "≥10 min apart, ≤3 per hour" ceilings hold within
one agent lifetime, not across restarts. In practice the exposure is small — a restart also re-arms
the 3-minute settle window and the two-consecutive-bad-probes rule — but a crash-looping agent could
heal more often than the ceiling implies. Not worth persisting state for today; worth knowing before
anyone quotes the ceiling as a hard guarantee.

## 7. Deliverables

- `c0966d7` — v0.92.0: the watchdog, the report block, config, tests.
- `0e8fd81` — the sudoers grant + capability rows (the live finding).
- `98adb72` — v0.92.1: supersede + version bump.
- Published: `felhom-agent` **0.92.1** / `7424bc1c3c533eff…` (0.92.0 superseded).
- Live on felhom-pve: binary 0.92.1 + the new sudoers file.

## 8. Operator actions outstanding

1. ~~STOP-2~~ — **DONE 2026-07-21, passed** (§6b).
2. ~~STOP-3~~ — **DONE 2026-07-21.** Manifest Agent → **0.92.1**, sha matches the published artifact
   byte for byte; MinAgent → 0.92.1; PBS wrapper sha unchanged (`104db0a4…`, correct — the wrapper
   was not touched); controller floor → 0.156.0. The host page shows all four `guestnet-*`
   capability rows **ok**, which is the fleet-visible proof of the sudoers grant.
3. ~~Revert `log_level` to `info`~~ — **DONE** (13:17 CEST, after the quiet window closed; agent
   restarted clean, caps `68/68 ok, degraded=0`, watchdog back up). The temporary raise is recorded
   here only so the journald volume change is explainable; `/root/agent.json.bak-debuglevel` remains
   as the pre-change copy.