Add MQTT backup reporting and trigger listener

bin/mqtt-trigger-listener.sh

@@ -0,0 +1,24 @@
+#!/usr/bin/env bash
+# Listen for an authenticated JSON command and run the backup pipeline.
+set -Eeuo pipefail
+SCRIPT_DIR="$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")/.." && pwd -P)"
+. "$SCRIPT_DIR/lib/common.sh"
+. "$SCRIPT_DIR/lib/mqtt.sh"
+
+require_command jq
+require_command mosquitto_sub
+[[ -n "$MQTT_HOST" ]] || die "MQTT_HOST is not configured"
+mqtt_common_args
+log MQTT "Listening on $MQTT_COMMAND_TOPIC"
+
+# Never replay a retained command after this listener or the MQTT broker restarts.
+# Home Assistant should also publish run commands without the retain flag.
+mosquitto_sub "${MQTT_ARGS[@]}" -R -t "$MQTT_COMMAND_TOPIC" | while IFS= read -r payload; do
+  action="$(jq -er '.action // empty' <<<"$payload" 2>/dev/null || true)"
+  if [[ "$action" != "run" ]]; then
+    log WARN "Ignored invalid MQTT command"
+    continue
+  fi
+  log MQTT "Accepted backup run command"
+  "$SCRIPT_DIR/backup.sh" || log ERROR "MQTT-triggered backup failed"
+done