feat(sensor): add disabled-by-default connection-mode diagnostic sensor

Exposes whether a device is currently in observe (push) or poll mode,
for troubleshooting the observe-mode feature without digging through
logs. Disabled by default since it's not everyday-use information.

custom_components/localthings/sensor.py

@@ -3,9 +3,13 @@ from __future__ import annotations
 
 from homeassistant.components.sensor import SensorEntity, SensorDeviceClass, SensorStateClass
 from homeassistant.config_entries import ConfigEntry
+from homeassistant.const import EntityCategory
 from homeassistant.core import HomeAssistant
+from homeassistant.helpers.device_registry import DeviceInfo
 from homeassistant.helpers.entity_platform import AddEntitiesCallback
+from homeassistant.helpers.update_coordinator import CoordinatorEntity
 
+from .observe import MODE_OBSERVE, MODE_POLL
 from .registry.entities import SensorDesc
 
 from .const import DOMAIN
@@ -19,11 +23,13 @@ async def async_setup_entry(
     async_add_entities: AddEntitiesCallback,
 ) -> None:
     coordinator: LocalThingsCoordinator = hass.data[DOMAIN][entry.entry_id]
-    async_add_entities(
+    entities = [
         LocalThingsSensor(coordinator, b)
         for b in coordinator.bound
         if isinstance(b.desc, SensorDesc) and _is_included(b, coordinator)
-    )
+    ]
+    entities.append(LocalThingsConnectionModeSensor(coordinator))
+    async_add_entities(entities)
 
 
 class LocalThingsSensor(LocalThingsEntity, SensorEntity):
@@ -40,3 +46,29 @@ class LocalThingsSensor(LocalThingsEntity, SensorEntity):
     @property
     def native_value(self):
         return (self.coordinator.data or {}).get(self._state_key)
+
+
+class LocalThingsConnectionModeSensor(CoordinatorEntity[LocalThingsCoordinator], SensorEntity):
+    """Diagnostic sensor exposing whether this device is currently
+    receiving push notifications (observe mode) or being polled only.
+    Disabled by default — it's for troubleshooting, not everyday use."""
+
+    _attr_has_entity_name = True
+    _attr_name = 'Connection mode'
+    _attr_translation_key = 'connection_mode'
+    _attr_entity_category = EntityCategory.DIAGNOSTIC
+    _attr_entity_registry_enabled_default = False
+    _attr_device_class = SensorDeviceClass.ENUM
+    _attr_options = [MODE_OBSERVE, MODE_POLL]
+
+    def __init__(self, coordinator: LocalThingsCoordinator) -> None:
+        super().__init__(coordinator)
+        self._attr_unique_id = f"{DOMAIN}_{coordinator.device_serial}_connection_mode"
+
+    @property
+    def device_info(self) -> DeviceInfo:
+        return self.coordinator.device_info
+
+    @property
+    def native_value(self) -> str:
+        return self.coordinator.observe_mode

custom_components/localthings/strings.json

@@ -45,6 +45,12 @@
           "icestatus_stop": "Idle",
           "icestatus_run": "Making ice"
         }
+      },
+      "connection_mode": {
+        "state": {
+          "observe": "Push (observe)",
+          "poll": "Polling"
+        }
       }
     }
   },

custom_components/localthings/translations/en.json

@@ -45,6 +45,12 @@
           "icestatus_stop": "Idle",
           "icestatus_run": "Making ice"
         }
+      },
+      "connection_mode": {
+        "state": {
+          "observe": "Push (observe)",
+          "poll": "Polling"
+        }
       }
     }
   },

tests/localthings/test_sensor.py

@@ -6,6 +6,7 @@ from homeassistant.core import HomeAssistant
 from homeassistant.helpers import entity_registry as er
 
 from custom_components.localthings.const import DOMAIN
+from custom_components.localthings.observe import MODE_POLL
 
 
 async def test_sensors_registered(
@@ -45,3 +46,37 @@ async def test_sensor_state_from_coordinator(
     assert state.state not in ('unknown', 'unavailable'), (
         f"Sensor state is {state.state}"
     )
+
+
+async def test_connection_mode_sensor_registered_disabled_by_default(
+    hass: HomeAssistant, mock_entry, mock_coordinator_session
+) -> None:
+    """The connection-mode diagnostic sensor is registered but disabled by
+    default — it's for troubleshooting, not everyday use."""
+    await hass.config_entries.async_setup(mock_entry.entry_id)
+    await hass.async_block_till_done()
+
+    ent_reg = er.async_get(hass)
+    entries = er.async_entries_for_config_entry(ent_reg, mock_entry.entry_id)
+    mode_entries = [e for e in entries if e.unique_id.endswith('_connection_mode')]
+    assert len(mode_entries) == 1
+    entry = mode_entries[0]
+    assert entry.disabled_by is not None
+    assert entry.entity_category == 'diagnostic'
+
+
+async def test_connection_mode_sensor_reflects_coordinator_mode(
+    hass: HomeAssistant, mock_entry, mock_coordinator_session
+) -> None:
+    """native_value reads coordinator.observe_mode directly, live."""
+    from custom_components.localthings.sensor import LocalThingsConnectionModeSensor
+
+    await hass.config_entries.async_setup(mock_entry.entry_id)
+    await hass.async_block_till_done()
+
+    coordinator = hass.data[DOMAIN][mock_entry.entry_id]
+    sensor = LocalThingsConnectionModeSensor(coordinator)
+    assert sensor.native_value == MODE_POLL
+
+    coordinator._observe._set_mode('observe')
+    assert sensor.native_value == 'observe'