Found while shutting down: unplugging the LCXL took midiviz's ALSA
source with it, the process exited cleanly, and Restart=on-failure did
not fire. The permanent lens is only permanent while the board stays
plugged -- which is the same resolve-once stale-binding shape as the
zombie driver this session was opened to fix. lcxl-leds.py already has
the fix pattern (re-resolve per send, cache invalidated on failure).