Refactor BLE layer for 24/7 reliability

- Replace raw BleakClient with establish_connection from
  bleak-retry-connector (retries, GATT service cache, proxy-aware)
- Replace fragile asyncio.Event with asyncio.Queue for response frames,
  drain stale data on each connection to prevent cross-cycle leakage
- Register BLE advertisement callback to keep BLEDevice reference fresh
  across ESPHome proxy path changes
- Remove asyncio.sleep(2) device lookup hack
- Increase poll timeout floor from 10s to 20s
- Increase failure tolerance from 3 to 5 consecutive misses
- Bump default poll interval to 30s, min to 15s (halves connection churn)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

custom_components/xiaoxiang_bms/__init__.py

@@ -1,8 +1,15 @@
 """Xiaoxiang Smart BMS — Home Assistant integration."""
 from __future__ import annotations
 
+from homeassistant.components.bluetooth import (
+    BluetoothChange,
+    BluetoothScanningMode,
+    BluetoothServiceInfoBleak,
+    async_register_callback,
+)
+from homeassistant.components.bluetooth.match import ADDRESS, BluetoothCallbackMatcher
 from homeassistant.config_entries import ConfigEntry
-from homeassistant.core import HomeAssistant
+from homeassistant.core import HomeAssistant, callback
 
 from .const import CONF_ADDRESS, CONF_POLL_INTERVAL, DEFAULT_POLL_INTERVAL, DOMAIN
 from .coordinator import BmsCoordinator
@@ -16,13 +23,31 @@ async def async_setup_entry(hass: HomeAssistant, entry: ConfigEntry) -> bool:
     poll_interval = entry.options.get(CONF_POLL_INTERVAL, DEFAULT_POLL_INTERVAL)
 
     coordinator = BmsCoordinator(hass, address, poll_interval, name=entry.title)
+
+    # Keep the coordinator's BLE device reference fresh via advertisement callback.
+    # This avoids stale transport paths when ESPHome proxies cycle.
+    @callback
+    def _async_update_ble(
+        service_info: BluetoothServiceInfoBleak,
+        change: BluetoothChange,
+    ) -> None:
+        coordinator._ble_device = service_info.device
+
+    entry.async_on_unload(
+        async_register_callback(
+            hass,
+            _async_update_ble,
+            BluetoothCallbackMatcher({ADDRESS: address}),
+            BluetoothScanningMode.PASSIVE,
+        )
+    )
+
     await coordinator.async_setup()
     await coordinator.async_config_entry_first_refresh()
 
     hass.data.setdefault(DOMAIN, {})[entry.entry_id] = coordinator
     await hass.config_entries.async_forward_entry_setups(entry, PLATFORMS)
 
-    # Reload the entry when options (e.g. poll interval) change
     entry.async_on_unload(entry.add_update_listener(_async_update_listener))
 
     return True