Retire nut-udev-restart.sh to unused/

It was meant to restart the NUT driver from a udev RUN+= when the UPS
re-enumerates on USB, but was never wired up: 50-nut-ups.rules only sets MODE
and GROUP.

systemd already covers the case. nut-driver@ups.service is Restart=always
with RestartUSec=15s, so the driver is retried indefinitely and reattaches to
a new device node unaided.

It would also not have worked reliably. systemd-udevd kills RUN+= handlers
still alive when the event completes, so the backgrounded subshell could be
killed mid-sleep, and upsdrvctl would run the driver outside the unit's
supervision, competing with systemd's own restarts.

Kept with a header recording the rule-based alternative if faster recovery is
ever wanted.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

unused/nut-udev-restart.sh

@@ -0,0 +1,36 @@
+#!/bin/bash
+# RETIRED. Kept for reference only.
+#
+# Intended to be called from a udev RUN+= when the UPS re-enumerates on USB, to
+# restart the NUT driver so it reattaches to the new device node. It was never
+# wired up: /etc/udev/rules.d/50-nut-ups.rules only sets MODE and GROUP.
+#
+# Superseded by systemd. nut-driver@ups.service is Restart=always with
+# RestartUSec=15s, so the driver is already retried indefinitely and picks up a
+# new device node on its own. This script would only save about 13 seconds.
+#
+# It would also not work reliably as written:
+#
+#   - systemd-udevd runs RUN+= handlers in a cgroup and kills whatever is still
+#     alive when the event completes, so the backgrounded subshell can be killed
+#     mid-sleep and the restart never happens. Long-running work belongs in
+#     ENV{SYSTEMD_WANTS}= or RUN+="systemctl --no-block ...".
+#   - upsdrvctl starts the driver outside nut-driver@ups.service's supervision,
+#     while stopping it makes systemd spawn a competing replacement.
+#
+# If faster recovery is ever wanted, drop the script and put the trigger in the
+# rule instead:
+#
+#   SUBSYSTEM=="usb", ATTR{idVendor}=="0764", ATTR{idProduct}=="0601", \
+#     ACTION=="add", RUN+="/usr/bin/systemctl --no-block restart nut-driver@ups.service"
+
+(
+    # small delay so the USB device is fully settled before restarting driver
+    sleep 2
+
+    # stop and start the driver
+    /sbin/upsdrvctl stop
+    /sbin/upsdrvctl start
+) &
+
+exit 0