nas+nuc: cold boot verified; record what clearing the metadata errors took

Both hosts were powered off and brought back from a cold start, which is
the first real test of everything built on 2026-08-30.

nas: both pools imported from /etc/zfs/zpool.cache, all instances
autostarted, NFS exports republished, 0 failed units. nuc: /dev/dri
present with 0 i915 warnings (booted with the display unplugged), NFS
auto-remounted, VAAPI transcode at 9.5x realtime.

Records the ordering that actually cleared tank's inherited
<metadata>:<0x0> and <0x3d>: a scrub alone found 0 errors and repaired 0B
but left them, and a plain `zpool clear` afterwards did not drop them —
ZFS flushes the persistent error log on a scrub run *after* the clear.
That matters beyond tidiness, because while those entries stand
`zpool status -x` reports the pool unhealthy forever and zpool-health.sh
cannot signal anything new.

Two kiosk corrections, both from observed behaviour:

- the Pioneer DAC being switched off is the most likely cause of
  "video, no sound" — asound.conf pins the ALSA default to it by card
  name, so `default` fails to open outright and mpv falls back to null
  silently. Adds the one-line aplay check.
- hotplugging the display makes cage exit once and Restart=on-failure
  recovers it ~5s later. Do NOT restart it by hand; check
  ActiveEnterTimestamp against the hotplug time first.

Also flags that the OS mirror is still untested with a disk physically
unplugged — it is a guess until then.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

nuc/jellyfin-client.md

@@ -447,6 +447,23 @@ incus exec jellyfin-client -- udevadm info /dev/input/event0    # udev db visibl
   visible (#2); check `run-udev.mount` is active.
 - **Video OK, no sound; JMP log shows `AO: [null]`** → ALSA default broken
   (#3); check `/etc/asound.conf` and the card name in `aplay -l`.
+  **Most common cause: the Pioneer DAC is simply switched off.**
+  `/etc/asound.conf` pins the default to it *by card name* (`Device`), so
+  with the amp off the name does not exist and `default` fails to open —
+  mpv then falls back to null silently: picture, no sound, no error.
+  One-line check before blaming anything else:
+  ```sh
+  incus exec jellyfin-client -- su -s /bin/bash kiosk -c 'aplay -D default -d 1 /usr/share/sounds/alsa/Front_Center.wav'
+  ```
+  `audio open error: No such device` = amp is off. Power it on; no
+  restart needed, JMP opens the device per playback.
+- **Display hotplugged after boot → cage exits once, then recovers by
+  itself.** If the kiosk started with no outputs, plugging the HDMI in
+  makes cage fail (`Failed with result 'exit-code'`); the unit's
+  `Restart=on-failure` / `RestartSec=5` restarts it ~5 s later, this time
+  with the display present. **Do not restart it by hand** — check
+  `systemctl show jellyfin-kiosk -p ActiveEnterTimestamp` first and only
+  intervene if the timestamp predates the hotplug. Verified 2026-08-31.
 - **Keyboard plugged in after boot isn't seen** — the host udev db is live
   through the bind, but udev hotplug *events* don't cross the container's
   network namespace, so cage only enumerates at startup. Re-plugging the