PLN: 'media keys dont work' + 'tried bluetooth headset couldnt get sound there'.
Cause was neither:

    wireplumber        failed (start-limit-hit)
    Sinks:  100. Dummy Output      <- the ONLY sink
    0 bluez objects

pipewire is the graph; wireplumber is the session manager that puts DEVICES in
it. Without it there are no device nodes at all -- every hardware sink vanishes,
PipeWire invents Dummy Output, media keys act on nothing, and a Bluetooth
headset cannot appear however well it pairs. It reads exactly like dead
hardware.

The trap is StartLimitBurst=5 / 5min with Restart=on-failure. Five hand-issued
restarts inside two minutes exhausted it, and from then on restarting AGAIN
cannot work. Cure is reset-failed, then start. Third instance of this exact
shape in one session after parvagues-sc twice: on this box, 'X will not start'
means check reset-failed first.

rig-doctor's check_pipewire tested pipewire on PATH, pw-jack on PATH, and
pipewire.service is-active -- and pipewire.service was ACTIVE for the whole
outage, so the check was green while the box had no audio at all. Presence
versus function again. It now also asserts wireplumber is active and that the
graph holds at least one real output (alsa_output/bluez_output, never
auto_null/Dummy), FAILs with the reset-failed cure in the fix field, and WARNs
on a dummy or unset default. It caught a live regression the first time it ran.

The headset itself was only MUTED: bluez_card active profile was already
a2dp-sink, and the sink read '[vol: 0.20 MUTED]' -- per-device state wireplumber
persists. Unmuted by NAME, because the BT node id moves between calls while the
device reconnects. Not caused by the quantum/mute testing, which ran at 00:10
with no BT device connected and left force-quantum verified at 0.

latency-lens --print-config used to hand over 'systemctl --user restart pipewire
pipewire-pulse wireplumber' with no warning, which repeated is precisely this
trap. It now says ONCE, states the consequence, gives the cure, and points at
the runtime setting that needs no restart.

Doctor: 48 checks, 0 fail, 10 warn, 38 pass.