Backlight retention re-added

gaugemqttcontinuous.py

@@ -397,6 +397,36 @@ def set_status_led(gauge_idx, led_type, state):
     leds_bl.write()
 
 
+def publish_backlight_states(client):
+    """Publish current backlight state for all gauges as retained MQTT messages."""
+    for i in range(num_gauges):
+        gt = gauge_topics[i]
+        r, g, b = backlight_color[i]
+        brightness = backlight_brightness[i]
+        state = {
+            "state": "ON" if backlight_on[i] else "OFF",
+            "color_mode": "rgb",
+            "brightness": int(brightness * 2.55),
+            "color": {"r": r, "g": g, "b": b},
+        }
+        try:
+            client.publish(gt["led_bl_state"], ujson.dumps(state), retain=True)
+        except Exception as e:
+            log_err(f"Backlight state publish failed for gauge {i}: {e}")
+
+
+def _flush_backlight_state():
+    global _bl_dirty_since
+    if _bl_dirty_since is None:
+        return
+    if utime.ticks_diff(utime.ticks_ms(), _bl_dirty_since) < _BL_SAVE_DELAY_MS:
+        return
+    if client_ref is None:
+        return
+    publish_backlight_states(client_ref)
+    _bl_dirty_since = None
+    info("Backlight state flushed to MQTT")
+
 
 def _publish(topic, payload, retain=False):
     """Safely publish MQTT message, returning True on success."""