diff --git a/app/integrations/expose.py b/app/integrations/expose.py
index 698bb9a..2a1423c 100644
--- a/app/integrations/expose.py
+++ b/app/integrations/expose.py
@@ -373,12 +373,36 @@ register_provider(_modbus_provider)
 def _energy_cost_provider(session: Session) -> list[ExposableEntity]:
     """Enumerate ExposableEntity objects for the energy cost subsystem.
 
-    Produces 4 sensor entities grouped under a single HA device "Energy Cost":
+    Produces 6 sensor entities grouped under a single HA device whose identity
+    is anchored to the **current active electricity meter**:
 
     - ``buy_price_now``         — current effective buy price (EUR/kWh or local currency).
     - ``sell_price_now``        — current effective sell price (EUR/kWh or local currency).
-    - ``import_cost_total``     — cumulative import cost (total_increasing, monetary).
-    - ``export_revenue_total``  — cumulative export revenue (total_increasing, monetary).
+    - ``import_cost_total``     — cumulative import cost (total, monetary).
+    - ``export_revenue_total``  — cumulative export revenue (total, monetary).
+    - ``import_cost_today``     — today's import cost (total_increasing, monetary).
+    - ``export_revenue_today``  — today's export revenue (total_increasing, monetary).
+
+    Active meter requirement
+    ------------------------
+    **If no active electricity meter exists, the provider returns ``[]``.**
+    No energy-cost entities are exposed to HA until a meter has been declared.
+    This prevents spurious sensor creation with an undefined device identity.
+
+    HA device identity (换表 → 新 sensor)
+    --------------------------------------
+    ``identifiers[1]`` is set to the active meter's **uuid** (not the fixed
+    string ``"energy-cost"``).  ``ha_discovery.py`` uses ``identifiers[1]`` as
+    the MQTT node_id and as part of the ``unique_id`` for every entity.
+    Declaring a new active electricity meter produces a new uuid → new node_id /
+    unique_id → HA creates a brand-new sensor, cleanly isolating post-swap data.
+
+    Entity key stability
+    --------------------
+    Entity keys remain the fixed stable strings (``"energy.buy_price_now"`` etc.),
+    **not** derived from the meter uuid.  The ``exposed_entity_toggle`` table uses
+    keys as its primary handle; keeping them stable means toggled-on entities stay
+    enabled after a meter swap without requiring the user to re-tick them.
 
     Current-price algorithm (source-agnostic, with fallback)
     ---------------------------------------------------------
@@ -399,8 +423,9 @@ def _energy_cost_provider(session: Session) -> list[ExposableEntity]:
     Cumulative totals
     -----------------
     ``SUM(import_cost)`` and ``SUM(export_revenue)`` over **all non-degraded**
-    ``energy_cost_period`` rows.  Degraded rows carry 0 costs and are excluded
-    to avoid double-counting when they are later overwritten by real values.
+    ``energy_cost_period`` rows within the current meter's window.  Degraded rows
+    carry 0 costs and are excluded to avoid double-counting when they are later
+    overwritten by real values.
 
     Currency
     --------
@@ -414,16 +439,37 @@ def _energy_cost_provider(session: Session) -> list[ExposableEntity]:
       - ``"energy.sell_price_now"``
       - ``"energy.import_cost_total"``
       - ``"energy.export_revenue_total"``
+      - ``"energy.import_cost_today"``
+      - ``"energy.export_revenue_today"``
 
     DeviceInfo identifiers
     ----------------------
-    **Two-element tuple** ``("energy-cost", "energy-cost")`` so that
-    ``ha_discovery.py``'s ``entity.device.identifiers[1]`` is always valid
-    (the service uses index [1] as the node_id throughout).
+    **Two-element tuple** ``("energy-cost", meter.uuid)`` so that
+    ``ha_discovery.py``'s ``entity.device.identifiers[1]`` resolves to the
+    meter uuid (used as the MQTT node_id and unique_id seed throughout).
     """
-    from app.models.energy import EnergyCostPeriod  # local import to avoid circular
+    from app.models.energy import EnergyCostPeriod, Meter  # local import to avoid circular
+    from sqlalchemy import select
 
-    # --- Determine currency and representative pricing from the latest non-degraded row ---
+    # --- Require an active electricity meter; return [] if none exists ---
+    # Using an inline query (ended_at IS NULL) rather than a service-layer helper
+    # to avoid a new public dependency and remain consistent with the value_getter
+    # implementations below (which use the same inline pattern).
+    active_meter: Meter | None = session.execute(
+        select(Meter)
+        .where(
+            Meter.commodity == "electricity",
+            Meter.ended_at.is_(None),
+        )
+        .limit(1)
+    ).scalar_one_or_none()
+
+    if active_meter is None:
+        # No active electricity meter → do not expose any energy-cost entities.
+        # HA will not see these sensors until a meter is declared.
+        return []
+
+    # --- Determine currency from the latest non-degraded row ---
 
     latest_period: EnergyCostPeriod | None = (
         session.query(EnergyCostPeriod)
@@ -436,13 +482,15 @@ def _energy_cost_provider(session: Session) -> list[ExposableEntity]:
     if latest_period is not None and latest_period.currency:
         currency = latest_period.currency
 
-    # --- Shared DeviceInfo (2-element identifiers — required by ha_discovery.py [1] access) ---
+    # --- Shared DeviceInfo anchored to the active meter's uuid ---
+    # identifiers[1] = meter.uuid drives the MQTT node_id and unique_id in
+    # ha_discovery.py.  Swapping the meter produces a new uuid → new HA sensor.
     # provides_availability=False: the energy-cost device has only sensors and no
     # online/offline heartbeat, so its entities must be "always available" in HA.
     # (Otherwise HA shows them unavailable despite state being published.)
     device_info = DeviceInfo(
-        identifiers=("energy-cost", "energy-cost"),
-        name="Energy Cost",
+        identifiers=("energy-cost", active_meter.uuid),
+        name=f"Energy Cost ({active_meter.label})",
         provides_availability=False,
     )
 
diff --git a/tests/test_energy_expose.py b/tests/test_energy_expose.py
index 5856071..d495680 100644
--- a/tests/test_energy_expose.py
+++ b/tests/test_energy_expose.py
@@ -164,9 +164,18 @@ def energy_db(tmp_path: Path):
 
 
 def test_build_catalog_contains_6_energy_cost_entities(energy_db) -> None:
-    """build_catalog must include all 6 energy_cost sensor entities (4 original + 2 daily)."""
+    """build_catalog must include all 6 energy_cost sensor entities (4 original + 2 daily).
+
+    FUE-T05: provider requires an active electricity meter.  Insert one so the
+    provider produces its 6 entities.
+    """
     from app.integrations.expose import build_catalog
 
+    now = datetime(2026, 1, 1, 0, 0, tzinfo=timezone.utc)
+    with Session(energy_db) as session:
+        _make_active_meter(session, started_at=now)
+        session.commit()
+
     with Session(energy_db) as session:
         catalog = build_catalog(session)
 
@@ -190,9 +199,17 @@ def test_build_catalog_contains_6_energy_cost_entities(energy_db) -> None:
 
 
 def test_cumulative_entities_have_total_state_class(energy_db) -> None:
-    """import_cost_total and export_revenue_total must have state_class='total'."""
+    """import_cost_total and export_revenue_total must have state_class='total'.
+
+    FUE-T05: provider requires an active electricity meter.
+    """
     from app.integrations.expose import build_catalog
 
+    now = datetime(2026, 1, 1, 0, 0, tzinfo=timezone.utc)
+    with Session(energy_db) as session:
+        _make_active_meter(session, started_at=now)
+        session.commit()
+
     with Session(energy_db) as session:
         catalog = build_catalog(session)
 
@@ -206,9 +223,17 @@ def test_cumulative_entities_have_total_state_class(energy_db) -> None:
 
 
 def test_cumulative_entities_have_monetary_device_class(energy_db) -> None:
-    """import_cost_total and export_revenue_total must have device_class='monetary'."""
+    """import_cost_total and export_revenue_total must have device_class='monetary'.
+
+    FUE-T05: provider requires an active electricity meter.
+    """
     from app.integrations.expose import build_catalog
 
+    now = datetime(2026, 1, 1, 0, 0, tzinfo=timezone.utc)
+    with Session(energy_db) as session:
+        _make_active_meter(session, started_at=now)
+        session.commit()
+
     with Session(energy_db) as session:
         catalog = build_catalog(session)
 
@@ -222,9 +247,17 @@ def test_cumulative_entities_have_monetary_device_class(energy_db) -> None:
 
 
 def test_all_energy_entities_are_sensors(energy_db) -> None:
-    """All 6 energy_cost entities must have component='sensor'."""
+    """All 6 energy_cost entities must have component='sensor'.
+
+    FUE-T05: provider requires an active electricity meter.
+    """
     from app.integrations.expose import build_catalog
 
+    now = datetime(2026, 1, 1, 0, 0, tzinfo=timezone.utc)
+    with Session(energy_db) as session:
+        _make_active_meter(session, started_at=now)
+        session.commit()
+
     with Session(energy_db) as session:
         catalog = build_catalog(session)
 
@@ -243,9 +276,17 @@ def test_all_energy_entities_are_sensors(energy_db) -> None:
 
 
 def test_energy_cost_entities_default_to_disabled(energy_db) -> None:
-    """All 6 energy_cost entities must default to enabled=False (no toggle row)."""
+    """All 6 energy_cost entities must default to enabled=False (no toggle row).
+
+    FUE-T05: provider requires an active electricity meter.
+    """
     from app.integrations.expose import build_catalog
 
+    now = datetime(2026, 1, 1, 0, 0, tzinfo=timezone.utc)
+    with Session(energy_db) as session:
+        _make_active_meter(session, started_at=now)
+        session.commit()
+
     with Session(energy_db) as session:
         catalog = build_catalog(session)
 
@@ -264,10 +305,14 @@ def test_energy_cost_entities_default_to_disabled(energy_db) -> None:
 
 
 def test_buy_price_getter_reads_tibber_snapshot(energy_db) -> None:
-    """buy_price_now value_getter must return the 'buy' price from tibber snapshot."""
+    """buy_price_now value_getter must return the 'buy' price from tibber snapshot.
+
+    FUE-T05: provider requires an active electricity meter.
+    """
     from app.integrations.expose import build_catalog
 
     t0 = datetime(2025, 1, 1, 12, 0, tzinfo=timezone.utc)
+    meter_start = datetime(2025, 1, 1, 0, 0, tzinfo=timezone.utc)
     tibber_pricing = {
         "kind": "tibber",
         "buy": "0.2850",
@@ -280,6 +325,7 @@ def test_buy_price_getter_reads_tibber_snapshot(energy_db) -> None:
     }
 
     with Session(energy_db) as session:
+        _make_active_meter(session, started_at=meter_start)
         _make_period(
             session,
             period_start=t0,
@@ -304,10 +350,14 @@ def test_buy_price_getter_reads_tibber_snapshot(energy_db) -> None:
 
 
 def test_sell_price_getter_reads_tibber_snapshot(energy_db) -> None:
-    """sell_price_now value_getter must return the 'sell' price from tibber snapshot."""
+    """sell_price_now value_getter must return the 'sell' price from tibber snapshot.
+
+    FUE-T05: provider requires an active electricity meter.
+    """
     from app.integrations.expose import build_catalog
 
     t0 = datetime(2025, 1, 1, 12, 15, tzinfo=timezone.utc)
+    meter_start = datetime(2025, 1, 1, 0, 0, tzinfo=timezone.utc)
     tibber_pricing = {
         "kind": "tibber",
         "buy": "0.3100",
@@ -320,6 +370,7 @@ def test_sell_price_getter_reads_tibber_snapshot(energy_db) -> None:
     }
 
     with Session(energy_db) as session:
+        _make_active_meter(session, started_at=meter_start)
         _make_period(
             session,
             period_start=t0,
@@ -344,10 +395,14 @@ def test_sell_price_getter_reads_tibber_snapshot(energy_db) -> None:
 
 
 def test_buy_price_getter_reads_manual_snapshot(energy_db) -> None:
-    """buy_price_now value_getter must return 'buy_normal' from manual pricing snapshot."""
+    """buy_price_now value_getter must return 'buy_normal' from manual pricing snapshot.
+
+    FUE-T05: provider requires an active electricity meter.
+    """
     from app.integrations.expose import build_catalog
 
     t0 = datetime(2025, 2, 1, 8, 0, tzinfo=timezone.utc)
+    meter_start = datetime(2025, 2, 1, 0, 0, tzinfo=timezone.utc)
     manual_pricing = {
         "kind": "manual",
         "buy_dal": "0.2500",
@@ -359,6 +414,7 @@ def test_buy_price_getter_reads_manual_snapshot(energy_db) -> None:
     }
 
     with Session(energy_db) as session:
+        _make_active_meter(session, started_at=meter_start)
         _make_period(
             session,
             period_start=t0,
@@ -384,10 +440,14 @@ def test_buy_price_getter_reads_manual_snapshot(energy_db) -> None:
 
 
 def test_sell_price_getter_reads_manual_snapshot(energy_db) -> None:
-    """sell_price_now value_getter must return 'sell_normal' from manual pricing snapshot."""
+    """sell_price_now value_getter must return 'sell_normal' from manual pricing snapshot.
+
+    FUE-T05: provider requires an active electricity meter.
+    """
     from app.integrations.expose import build_catalog
 
     t0 = datetime(2025, 2, 1, 8, 15, tzinfo=timezone.utc)
+    meter_start = datetime(2025, 2, 1, 0, 0, tzinfo=timezone.utc)
     manual_pricing = {
         "kind": "manual",
         "buy_dal": "0.2500",
@@ -399,6 +459,7 @@ def test_sell_price_getter_reads_manual_snapshot(energy_db) -> None:
     }
 
     with Session(energy_db) as session:
+        _make_active_meter(session, started_at=meter_start)
         _make_period(
             session,
             period_start=t0,
@@ -539,9 +600,19 @@ def test_cumulative_getter_excludes_degraded_import_cost_row(energy_db) -> None:
 
 
 def test_buy_price_getter_returns_none_with_no_periods(energy_db) -> None:
-    """buy_price_now value_getter must return None when no non-degraded periods exist."""
+    """buy_price_now value_getter must return None when no non-degraded periods exist.
+
+    FUE-T05: provider requires an active electricity meter.  Insert one so the
+    entity is present in the catalog; then verify the value_getter returns None
+    (no periods → no pricing snapshot).
+    """
     from app.integrations.expose import build_catalog
 
+    now = datetime(2026, 1, 1, 0, 0, tzinfo=timezone.utc)
+    with Session(energy_db) as session:
+        _make_active_meter(session, started_at=now)
+        session.commit()
+
     with Session(energy_db) as session:
         catalog = build_catalog(session)
         buy_entry = next(
@@ -553,9 +624,17 @@ def test_buy_price_getter_returns_none_with_no_periods(energy_db) -> None:
 
 
 def test_sell_price_getter_returns_none_with_no_periods(energy_db) -> None:
-    """sell_price_now value_getter must return None when no non-degraded periods exist."""
+    """sell_price_now value_getter must return None when no non-degraded periods exist.
+
+    FUE-T05: provider requires an active electricity meter.
+    """
     from app.integrations.expose import build_catalog
 
+    now = datetime(2026, 1, 1, 0, 0, tzinfo=timezone.utc)
+    with Session(energy_db) as session:
+        _make_active_meter(session, started_at=now)
+        session.commit()
+
     with Session(energy_db) as session:
         catalog = build_catalog(session)
         sell_entry = next(
@@ -567,12 +646,17 @@ def test_sell_price_getter_returns_none_with_no_periods(energy_db) -> None:
 
 
 def test_import_cost_getter_returns_none_with_no_non_degraded_periods(energy_db) -> None:
-    """import_cost_total value_getter must return None when only degraded rows exist."""
+    """import_cost_total value_getter must return None when only degraded rows exist.
+
+    FUE-T05: provider requires an active electricity meter.
+    """
     from app.integrations.expose import build_catalog
 
     t0 = datetime(2025, 5, 1, 0, 0, tzinfo=timezone.utc)
+    meter_start = datetime(2025, 5, 1, 0, 0, tzinfo=timezone.utc)
 
     with Session(energy_db) as session:
+        _make_active_meter(session, started_at=meter_start)
         # Only a degraded row → SUM returns None (no rows to aggregate)
         _make_period(session, period_start=t0, import_cost=0.0, degraded=True)
         session.commit()
@@ -590,9 +674,17 @@ def test_import_cost_getter_returns_none_with_no_non_degraded_periods(energy_db)
 
 
 def test_export_revenue_getter_returns_none_with_no_periods(energy_db) -> None:
-    """export_revenue_total value_getter must return None when no periods at all."""
+    """export_revenue_total value_getter must return None when no periods at all.
+
+    FUE-T05: provider requires an active electricity meter.
+    """
     from app.integrations.expose import build_catalog
 
+    now = datetime(2026, 1, 1, 0, 0, tzinfo=timezone.utc)
+    with Session(energy_db) as session:
+        _make_active_meter(session, started_at=now)
+        session.commit()
+
     with Session(energy_db) as session:
         catalog = build_catalog(session)
         export_entry = next(
@@ -673,14 +765,32 @@ def test_publish_states_noop_when_not_connected() -> None:
 def test_build_discovery_payload_no_index_error_for_energy_entities(energy_db) -> None:
     """build_discovery_payload must NOT raise IndexError for energy_cost entities.
 
-    Validates that the 2-element identifiers=('energy-cost', 'energy-cost') tuple
-    satisfies the ha_discovery.py requirement to access identifiers[1] as node_id.
-    This is a regression guard: if _energy_cost_provider used a 1-element tuple,
-    this call would raise IndexError.
+    FUE-T05: identifiers is now ('energy-cost', meter.uuid).
+    Validates that the 2-element identifiers tuple satisfies ha_discovery.py's
+    requirement to access identifiers[1] as node_id.
     """
     from app.integrations.expose import build_catalog
     from app.services.ha_discovery import build_discovery_payload
 
+    meter_uuid = "aaaaaaaa-bbbb-cccc-dddd-eeeeeeeeeeee"
+    meter_label = "Test Meter"
+    now = datetime(2026, 1, 1, 0, 0, tzinfo=timezone.utc)
+    with Session(energy_db) as session:
+        from app.models.energy import Meter as _M
+        m = _M(
+            label=meter_label,
+            commodity="electricity",
+            started_at=now,
+            ended_at=None,
+            reason="initial",
+            note=None,
+            created_at=now,
+        )
+        # Override the auto-generated uuid so we can assert on it deterministically.
+        m.uuid = meter_uuid
+        session.add(m)
+        session.commit()
+
     with Session(energy_db) as session:
         catalog = build_catalog(session)
 
@@ -688,36 +798,47 @@ def test_build_discovery_payload_no_index_error_for_energy_entities(energy_db) -
     assert len(energy_entries) == 6, "Expected 6 energy_cost entities in catalog"
 
     for entry in energy_entries:
+        # identifiers[1] must be the meter uuid (not "energy-cost").
+        assert entry.entity.device.identifiers[1] == meter_uuid, (
+            f"identifiers[1] must be meter uuid {meter_uuid!r}, "
+            f"got {entry.entity.device.identifiers[1]!r}"
+        )
         # Must not raise — specifically no IndexError from identifiers[1]
         topic, config = build_discovery_payload(entry.entity, "homeassistant")
 
-        # Basic sanity checks on the result.
-        # Note: ha_discovery._node_id() replaces hyphens with underscores, so
-        # identifiers[1]="energy-cost" → node_id="energy_cost" in the topic.
-        assert "energy_cost" in topic, (
-            f"Expected 'energy_cost' (hyphen→underscore) in discovery topic, got {topic!r}"
+        # node_id = identifiers[1] with hyphens → underscores
+        node_id = meter_uuid.replace("-", "_")
+        assert node_id in topic, (
+            f"Expected meter uuid node_id {node_id!r} in discovery topic, got {topic!r}"
         )
         assert topic.endswith("/config"), (
             f"Discovery topic must end with /config, got {topic!r}"
         )
         assert "unique_id" in config
-        # unique_id = "<identifiers[1]>_<key.replace('.','_')>"
-        # identifiers[1]="energy-cost" (hyphens NOT replaced in unique_id, only in node_id)
-        assert "energy" in config["unique_id"], (
-            f"unique_id must contain 'energy', got {config['unique_id']!r}"
+        # unique_id seed is identifiers[1] (meter uuid) + entity key
+        assert meter_uuid in config["unique_id"], (
+            f"unique_id must contain meter uuid, got {config['unique_id']!r}"
         )
         assert "device" in config
         assert "energy-cost" in config["device"]["identifiers"]
+        assert meter_uuid in config["device"]["identifiers"]
 
 
 def test_energy_cost_entities_omit_availability_so_ha_shows_them(energy_db) -> None:
     """The energy-cost device has no online/offline heartbeat, so its discovery
     config must NOT declare an availability topic — otherwise HA marks the
     entities ``unavailable`` forever even though state is being published.
+
+    FUE-T05: provider requires an active electricity meter.
     """
     from app.integrations.expose import build_catalog
     from app.services.ha_discovery import build_discovery_payload
 
+    now = datetime(2026, 1, 1, 0, 0, tzinfo=timezone.utc)
+    with Session(energy_db) as session:
+        _make_active_meter(session, started_at=now)
+        session.commit()
+
     with Session(energy_db) as session:
         catalog = build_catalog(session)
 
@@ -734,11 +855,23 @@ def test_energy_cost_entities_omit_availability_so_ha_shows_them(energy_db) -> N
 
 
 def test_energy_entity_discovery_topics_contain_correct_node_id() -> None:
-    """Discovery topic node_id for energy entities must be 'energy-cost' (hyphens → underscores)."""
+    """Discovery topic node_id for energy entities must be derived from meter uuid.
+
+    FUE-T05: identifiers[1] is now the active meter's uuid.
+    ha_discovery._node_id() replaces hyphens with underscores in identifiers[1]
+    to build the MQTT node_id.  This test verifies that the topic reflects the
+    meter uuid (not the old fixed 'energy-cost' string).
+    """
     from app.integrations.expose import DeviceInfo, ExposableEntity
     from app.services.ha_discovery import build_discovery_payload
 
-    device = DeviceInfo(identifiers=("energy-cost", "energy-cost"), name="Energy Cost")
+    meter_uuid = "12345678-abcd-ef00-1234-567890abcdef"
+    # identifiers[1] = meter uuid — this is what FUE-T05 sets.
+    device = DeviceInfo(
+        identifiers=("energy-cost", meter_uuid),
+        name="Energy Cost (Test Meter)",
+        provides_availability=False,
+    )
     entity = ExposableEntity(
         key="energy.import_cost_total",
         component="sensor",
@@ -751,10 +884,10 @@ def test_energy_entity_discovery_topics_contain_correct_node_id() -> None:
 
     topic, config = build_discovery_payload(entity, discovery_prefix="homeassistant")
 
-    # node_id: hyphens replaced with underscores → "energy_cost"
-    expected_node = "energy_cost"
+    # node_id: identifiers[1] = meter_uuid, hyphens → underscores
+    expected_node = meter_uuid.replace("-", "_")
     assert f"/{expected_node}/" in topic, (
-        f"Expected node_id 'energy_cost' in topic {topic!r}"
+        f"Expected meter uuid node_id {expected_node!r} in topic {topic!r}"
     )
     assert topic.startswith("homeassistant/sensor/"), (
         f"Topic must start with homeassistant/sensor/, got {topic!r}"
@@ -762,6 +895,10 @@ def test_energy_entity_discovery_topics_contain_correct_node_id() -> None:
     assert "state_class" in config
     assert config["state_class"] == "total"
     assert config.get("device_class") == "monetary"
+    # unique_id must contain the meter uuid
+    assert meter_uuid in config["unique_id"], (
+        f"unique_id must contain meter uuid, got {config['unique_id']!r}"
+    )
 
 
 # ---------------------------------------------------------------------------
@@ -770,15 +907,22 @@ def test_energy_entity_discovery_topics_contain_correct_node_id() -> None:
 
 
 def test_energy_entity_keys_are_stable_fixed_strings(energy_db) -> None:
-    """Entity keys must be fixed strings, not derived from DB ids or session state."""
+    """Entity keys must be fixed strings, not derived from DB ids or session state.
+
+    FUE-T05: provider requires an active electricity meter.  Keys remain the same
+    stable strings (``energy.*``) regardless of which meter is active — only the
+    DeviceInfo identifiers/name change, not the keys.
+    """
     from app.integrations.expose import build_catalog
     from datetime import timedelta
 
     t0 = datetime(2025, 6, 1, 0, 0, tzinfo=timezone.utc)
     t1 = t0 + timedelta(minutes=15)
+    meter_start = datetime(2025, 6, 1, 0, 0, tzinfo=timezone.utc)
 
-    # Insert two periods with different currencies to ensure key does not drift
+    # Insert active meter and first period
     with Session(energy_db) as session:
+        _make_active_meter(session, started_at=meter_start, label="Stable Key Meter")
         _make_period(
             session,
             period_start=t0,
@@ -831,12 +975,16 @@ def test_energy_entity_keys_are_stable_fixed_strings(energy_db) -> None:
 
 
 def test_energy_provider_registered_alongside_modbus(energy_db) -> None:
-    """Both modbus and energy_cost providers must be registered and produce entities."""
+    """Both modbus and energy_cost providers must be registered and produce entities.
+
+    FUE-T05: energy-cost provider requires an active electricity meter.
+    """
     from app.models.modbus import ModbusDevice
     from app.integrations.expose import build_catalog
 
     now = datetime.now(tz=timezone.utc)
     with Session(energy_db) as session:
+        _make_active_meter(session, started_at=now, label="Co-exist Electricity Meter")
         device = ModbusDevice(
             uuid="cccccccc-0000-0000-0000-000000000099",
             friendly_name="Co-exist Meter",
@@ -1273,9 +1421,16 @@ def reset_tariff(monkeypatch):
 
 
 def _insert_manual_period(energy_db) -> None:
-    """Insert a single non-degraded manual pricing period into energy_db."""
+    """Insert an active electricity meter + non-degraded manual pricing period into energy_db.
+
+    FUE-T05: the energy-cost provider requires an active electricity meter, so
+    this helper inserts one alongside the period so that build_catalog returns
+    the energy entities.
+    """
     t0 = datetime(2026, 3, 1, 10, 0, tzinfo=timezone.utc)
+    meter_start = datetime(2026, 3, 1, 0, 0, tzinfo=timezone.utc)
     with Session(energy_db) as session:
+        _make_active_meter(session, started_at=meter_start, label="Tariff Test Meter")
         _make_period(
             session,
             period_start=t0,
@@ -1385,11 +1540,15 @@ def test_sell_price_tariff_none_falls_back_to_normal(energy_db, reset_tariff) ->
 
 
 def test_tibber_buy_price_not_affected_by_tariff(energy_db, reset_tariff) -> None:
-    """Tibber buy_price_now must NOT be affected by the DSMR tariff — always uses 'buy' key."""
+    """Tibber buy_price_now must NOT be affected by the DSMR tariff — always uses 'buy' key.
+
+    FUE-T05: provider requires an active electricity meter.
+    """
     from app.integrations.expose import build_catalog
     from app.services.dsmr_ingest import set_current_tariff
 
     t0 = datetime(2026, 4, 1, 9, 0, tzinfo=timezone.utc)
+    meter_start = datetime(2026, 4, 1, 0, 0, tzinfo=timezone.utc)
     tibber_pricing = {
         "kind": "tibber",
         "buy": "0.3100",
@@ -1400,6 +1559,7 @@ def test_tibber_buy_price_not_affected_by_tariff(energy_db, reset_tariff) -> Non
     }
 
     with Session(energy_db) as session:
+        _make_active_meter(session, started_at=meter_start)
         _make_period(
             session,
             period_start=t0,
@@ -1421,11 +1581,15 @@ def test_tibber_buy_price_not_affected_by_tariff(energy_db, reset_tariff) -> Non
 
 
 def test_tibber_sell_price_not_affected_by_tariff(energy_db, reset_tariff) -> None:
-    """Tibber sell_price_now must NOT be affected by the DSMR tariff — always uses 'sell' key."""
+    """Tibber sell_price_now must NOT be affected by the DSMR tariff — always uses 'sell' key.
+
+    FUE-T05: provider requires an active electricity meter.
+    """
     from app.integrations.expose import build_catalog
     from app.services.dsmr_ingest import set_current_tariff
 
     t0 = datetime(2026, 4, 1, 9, 15, tzinfo=timezone.utc)
+    meter_start = datetime(2026, 4, 1, 0, 0, tzinfo=timezone.utc)
     tibber_pricing = {
         "kind": "tibber",
         "buy": "0.3100",
@@ -1436,6 +1600,7 @@ def test_tibber_sell_price_not_affected_by_tariff(energy_db, reset_tariff) -> No
     }
 
     with Session(energy_db) as session:
+        _make_active_meter(session, started_at=meter_start)
         _make_period(
             session,
             period_start=t0,
@@ -1461,9 +1626,17 @@ def test_tibber_sell_price_not_affected_by_tariff(energy_db, reset_tariff) -> No
 
 
 def test_daily_entities_in_catalog(energy_db) -> None:
-    """FU11: catalog must include import_cost_today and export_revenue_today."""
+    """FU11: catalog must include import_cost_today and export_revenue_today.
+
+    FUE-T05: provider requires an active electricity meter.
+    """
     from app.integrations.expose import build_catalog
 
+    now = datetime(2026, 1, 1, 0, 0, tzinfo=timezone.utc)
+    with Session(energy_db) as session:
+        _make_active_meter(session, started_at=now)
+        session.commit()
+
     with Session(energy_db) as session:
         catalog = build_catalog(session)
 
@@ -1476,9 +1649,17 @@ def test_daily_entities_in_catalog(energy_db) -> None:
 
 
 def test_daily_entities_have_total_increasing_state_class(energy_db) -> None:
-    """FU11: daily entities must have state_class='total_increasing' (not 'total')."""
+    """FU11: daily entities must have state_class='total_increasing' (not 'total').
+
+    FUE-T05: provider requires an active electricity meter.
+    """
     from app.integrations.expose import build_catalog
 
+    now = datetime(2026, 1, 1, 0, 0, tzinfo=timezone.utc)
+    with Session(energy_db) as session:
+        _make_active_meter(session, started_at=now)
+        session.commit()
+
     with Session(energy_db) as session:
         catalog = build_catalog(session)
 
@@ -1498,9 +1679,16 @@ def test_daily_entities_have_monetary_device_class(energy_db) -> None:
     allow it with total and total_increasing.  monetary+total_increasing is the correct
     combination for a non-negative, monotonically non-decreasing daily quantity that
     resets at local midnight.
+
+    FUE-T05: provider requires an active electricity meter.
     """
     from app.integrations.expose import build_catalog
 
+    now = datetime(2026, 1, 1, 0, 0, tzinfo=timezone.utc)
+    with Session(energy_db) as session:
+        _make_active_meter(session, started_at=now)
+        session.commit()
+
     with Session(energy_db) as session:
         catalog = build_catalog(session)
 
@@ -1514,9 +1702,17 @@ def test_daily_entities_have_monetary_device_class(energy_db) -> None:
 
 
 def test_daily_entities_default_disabled(energy_db) -> None:
-    """FU11: daily entities must default to enabled=False (no toggle row seeded)."""
+    """FU11: daily entities must default to enabled=False (no toggle row seeded).
+
+    FUE-T05: provider requires an active electricity meter.
+    """
     from app.integrations.expose import build_catalog
 
+    now = datetime(2026, 1, 1, 0, 0, tzinfo=timezone.utc)
+    with Session(energy_db) as session:
+        _make_active_meter(session, started_at=now)
+        session.commit()
+
     with Session(energy_db) as session:
         catalog = build_catalog(session)
 
@@ -1535,6 +1731,8 @@ def test_import_cost_today_getter_uses_local_day_window(energy_db) -> None:
     Setup: period at local 'today' (within today's UTC window), active contract.
     Timezone pinned to UTC. Verifies: value = metered_import + fixed_costs for 1 day
     (Principle C: today counts as elapsed if we're past local midnight — which UTC is).
+
+    FUE-T05: provider requires an active electricity meter.
     """
     from datetime import timedelta
     from unittest.mock import patch
@@ -1552,10 +1750,12 @@ def test_import_cost_today_getter_uses_local_day_window(energy_db) -> None:
 
     # Contract starting well before today
     effective_from = now_utc.replace(hour=0, minute=0, second=0, microsecond=0) - timedelta(days=30)
+    meter_start = now_utc.replace(hour=0, minute=0, second=0, microsecond=0) - timedelta(days=30)
 
     import_cost_today = 1.23
 
     with Session(energy_db) as session:
+        _make_active_meter(session, started_at=meter_start, label="Today Window Meter")
         _make_contract_with_version(
             session,
             values=_STANDING_VALUES,
@@ -1586,7 +1786,10 @@ def test_import_cost_today_getter_uses_local_day_window(energy_db) -> None:
 
 
 def test_export_revenue_today_getter_uses_local_day_window(energy_db) -> None:
-    """FU11: export_revenue_today getter returns value for today's local window."""
+    """FU11: export_revenue_today getter returns value for today's local window.
+
+    FUE-T05: provider requires an active electricity meter.
+    """
     from datetime import timedelta
     from unittest.mock import patch
     from zoneinfo import ZoneInfo
@@ -1599,9 +1802,11 @@ def test_export_revenue_today_getter_uses_local_day_window(energy_db) -> None:
         t0 = now_utc.replace(hour=0, minute=0, second=0, microsecond=0)
 
     effective_from = now_utc.replace(hour=0, minute=0, second=0, microsecond=0) - timedelta(days=30)
+    meter_start = now_utc.replace(hour=0, minute=0, second=0, microsecond=0) - timedelta(days=30)
     export_today = 0.75
 
     with Session(energy_db) as session:
+        _make_active_meter(session, started_at=meter_start, label="Today Export Meter")
         _make_contract_with_version(
             session,
             values=_STANDING_VALUES,
@@ -1629,12 +1834,17 @@ def test_export_revenue_today_getter_uses_local_day_window(energy_db) -> None:
 
 
 def test_daily_getter_returns_none_when_no_active_contract(energy_db) -> None:
-    """FU11: daily getters return None when no active contract exists."""
+    """FU11: daily getters return None when no active contract exists.
+
+    FUE-T05: provider requires an active electricity meter.
+    """
     from app.integrations.expose import build_catalog
 
     t0 = datetime(2026, 6, 25, 10, 0, tzinfo=timezone.utc)
+    meter_start = datetime(2026, 6, 25, 0, 0, tzinfo=timezone.utc)
 
     with Session(energy_db) as session:
+        _make_active_meter(session, started_at=meter_start, label="No Contract Meter")
         # Inactive contract
         _make_contract_with_version(
             session,
@@ -1665,12 +1875,17 @@ def test_daily_getter_returns_none_when_no_active_contract(energy_db) -> None:
 
 
 def test_daily_getter_returns_none_when_no_non_degraded_periods(energy_db) -> None:
-    """FU11: daily getters return None when only degraded rows exist."""
+    """FU11: daily getters return None when only degraded rows exist.
+
+    FUE-T05: provider requires an active electricity meter.
+    """
     from app.integrations.expose import build_catalog
 
     t0 = datetime(2026, 6, 25, 10, 0, tzinfo=timezone.utc)
+    meter_start = datetime(2026, 6, 25, 0, 0, tzinfo=timezone.utc)
 
     with Session(energy_db) as session:
+        _make_active_meter(session, started_at=meter_start, label="Degraded Only Meter")
         _make_contract_with_version(
             session,
             values=_STANDING_VALUES,
@@ -1773,29 +1988,61 @@ def test_cumulative_anchor_is_meter_started_at(energy_db) -> None:
 
 
 def test_cumulative_returns_none_when_no_active_meter(energy_db) -> None:
-    """M7-T04 None protection: no active electricity meter → import/export total = None.
+    """M7-T04 None protection: no active electricity meter → cumulative getters return None.
 
-    This is the key D2 None protection: without an active meter the anchor
-    cannot be resolved, so the getter returns None rather than a stale/wrong value.
+    FUE-T05 interaction: when no active meter exists, the provider returns [] and
+    entities are not in the catalog.  This test verifies the D2 None-protection of the
+    value_getters themselves (the inner functions) by calling them directly via a
+    catalog built with an active meter, then closing the meter (ended_at set) and
+    calling the getter in that closed-meter session.
+
+    This is the key D2 None protection: without an active meter the anchor cannot be
+    resolved, so the getter returns None rather than a stale/wrong value.
     Periods exist (non-degraded), but no Meter row with ended_at IS NULL is present.
     """
-    from app.integrations.expose import build_catalog
+    from app.models.energy import Meter
 
     t0 = datetime(2026, 3, 1, 10, 0, tzinfo=timezone.utc)
     t1 = datetime(2026, 3, 1, 10, 15, tzinfo=timezone.utc)
+    meter_start = datetime(2026, 3, 1, 0, 0, tzinfo=timezone.utc)
+    closed_at = datetime(2026, 3, 1, 12, 0, tzinfo=timezone.utc)
 
     with Session(energy_db) as session:
-        # No Meter row at all — cumulative getters must return None.
+        # Insert a meter that will later be closed.
+        m = Meter(
+            label="Will Be Closed",
+            commodity="electricity",
+            started_at=meter_start,
+            ended_at=None,
+            reason="initial",
+            note=None,
+            created_at=meter_start,
+        )
+        session.add(m)
         _make_period(session, period_start=t0, import_cost=1.00, degraded=False)
         _make_period(session, period_start=t1, export_revenue=0.50, degraded=False)
         session.commit()
+        meter_id = m.id
 
+    # Build the catalog while the meter is active to capture the value_getter callables.
+    from app.integrations.expose import build_catalog
     with Session(energy_db) as session:
         catalog = build_catalog(session)
         import_entry = next(e for e in catalog if e.entity.key == "energy.import_cost_total")
         export_entry = next(e for e in catalog if e.entity.key == "energy.export_revenue_total")
-        import_val = import_entry.entity.value_getter(session)
-        export_val = export_entry.entity.value_getter(session)
+        import_getter = import_entry.entity.value_getter
+        export_getter = export_entry.entity.value_getter
+
+    # Now close the meter (no active meter remains).
+    with Session(energy_db) as session:
+        m = session.get(Meter, meter_id)
+        m.ended_at = closed_at
+        session.commit()
+
+    # Call getters in a session where there is no active meter.
+    with Session(energy_db) as session:
+        import_val = import_getter(session)
+        export_val = export_getter(session)
 
     assert import_val is None, (
         f"import_cost_total must be None with no active meter, got {import_val!r}"
@@ -1917,11 +2164,12 @@ def test_daily_getters_unaffected_by_d2_meter_anchor(energy_db) -> None:
 
     D2 only changes the cumulative (*_total) anchor.  The *_today getters
     use today's local-day window [local midnight, local tomorrow midnight) in UTC.
-    They must continue to work correctly regardless of the meter anchor change,
-    and do NOT require an active meter (they use today's window directly).
+    They must work correctly regardless of which meter is active (meter started
+    30 days ago vs. 7 days ago — value must be the same: today's metered+fixed).
 
-    Setup: period 1h ago (today's local window, TZ=UTC), active contract.
-    Expected: value = import_today + fixed_for_today, independent of any meter.
+    FUE-T05: provider requires an active electricity meter to produce entities.
+    The test verifies that the *_today value is NOT influenced by the meter's
+    started_at (it uses today's window, not the meter anchor).
     """
     from decimal import Decimal
     from datetime import timedelta
@@ -1937,11 +2185,16 @@ def test_daily_getters_unaffected_by_d2_meter_anchor(energy_db) -> None:
         t0 = now_utc.replace(hour=0, minute=0, second=0, microsecond=0)
 
     effective_from = now_utc.replace(hour=0, minute=0, second=0, microsecond=0) - timedelta(days=30)
+    # Meter started far in the past — daily value must equal today's window value,
+    # NOT vary with the meter's started_at (that's the cumulative getter's job).
+    meter_start = now_utc.replace(hour=0, minute=0, second=0, microsecond=0) - timedelta(days=30)
     import_cost_today = 0.88
     export_today = 0.44
 
     with Session(energy_db) as session:
-        # No active meter added intentionally — daily getters must not need it.
+        # Active meter required by FUE-T05 provider; meter started_at must NOT
+        # affect the today getter's window (today's local midnight → tomorrow).
+        _make_active_meter(session, started_at=meter_start, label="Far-Past Meter")
         _make_contract_with_version(
             session,
             values=_STANDING_VALUES,
@@ -1977,10 +2230,241 @@ def test_daily_getters_unaffected_by_d2_meter_anchor(energy_db) -> None:
     expected_export = float(Decimal(str(export_today)) + daily_credit * 1)
 
     assert import_val == pytest.approx(expected_import, rel=1e-6), (
-        f"import_cost_today must use local-day window regardless of meter; "
+        f"import_cost_today must use local-day window regardless of meter started_at; "
         f"expected {expected_import}, got {import_val!r}"
     )
     assert export_val == pytest.approx(expected_export, rel=1e-6), (
-        f"export_revenue_today must use local-day window regardless of meter; "
+        f"export_revenue_today must use local-day window regardless of meter started_at; "
         f"expected {expected_export}, got {export_val!r}"
     )
+
+
+# ---------------------------------------------------------------------------
+# FUE-T05: energy-cost provider identity anchored to active electricity meter
+# ---------------------------------------------------------------------------
+
+
+def test_energy_cost_provider_returns_empty_when_no_active_meter(energy_db) -> None:
+    """FUE-T05 ①: no active electricity meter → provider returns [].
+
+    Without an active meter the energy-cost identifiers cannot be anchored,
+    so the provider must return an empty list.  HA will not see any energy-cost
+    sensor until a meter is declared.
+    """
+    from app.integrations.expose import _energy_cost_provider
+
+    with Session(energy_db) as session:
+        result = _energy_cost_provider(session)
+
+    assert result == [], (
+        f"Expected [] when no active electricity meter, got {result!r}"
+    )
+
+
+def test_energy_cost_provider_identifiers_match_meter_uuid(energy_db) -> None:
+    """FUE-T05 ②: with an active meter, identifiers[1] == meter.uuid.
+
+    The HA device identity is anchored to the active meter's uuid.  ha_discovery.py
+    uses identifiers[1] as the MQTT node_id and unique_id seed; changing the active
+    meter (meter swap) produces a new uuid → new node_id → new HA sensor.
+    """
+    from app.integrations.expose import _energy_cost_provider
+
+    meter_label = "Sunny Side Meter"
+    now = datetime(2026, 6, 1, 0, 0, tzinfo=timezone.utc)
+
+    with Session(energy_db) as session:
+        m = _make_active_meter(session, started_at=now, label=meter_label)
+        meter_uuid = m.uuid
+        session.commit()
+
+    with Session(energy_db) as session:
+        entities = _energy_cost_provider(session)
+
+    assert len(entities) == 6, f"Expected 6 entities, got {len(entities)}"
+    for entity in entities:
+        assert entity.device.identifiers == ("energy-cost", meter_uuid), (
+            f"identifiers must be ('energy-cost', meter.uuid); "
+            f"expected ('energy-cost', {meter_uuid!r}), "
+            f"got {entity.device.identifiers!r}"
+        )
+        assert meter_label in entity.device.name, (
+            f"device.name must contain meter label {meter_label!r}, "
+            f"got {entity.device.name!r}"
+        )
+
+
+def test_energy_cost_entity_keys_do_not_contain_meter_uuid(energy_db) -> None:
+    """FUE-T05 ③: entity keys remain stable 'energy.*' strings (no uuid injected).
+
+    Keys are the anchor for the toggle table; they must NOT change when the meter
+    changes.  Only identifiers[1] (node_id / unique_id) changes on a meter swap.
+    """
+    from app.integrations.expose import _energy_cost_provider
+
+    now = datetime(2026, 6, 1, 0, 0, tzinfo=timezone.utc)
+
+    with Session(energy_db) as session:
+        m = _make_active_meter(session, started_at=now, label="Key Stability Meter")
+        meter_uuid = m.uuid
+        session.commit()
+
+    with Session(energy_db) as session:
+        entities = _energy_cost_provider(session)
+
+    expected_keys = {
+        "energy.buy_price_now",
+        "energy.sell_price_now",
+        "energy.import_cost_total",
+        "energy.export_revenue_total",
+        "energy.import_cost_today",
+        "energy.export_revenue_today",
+    }
+    actual_keys = {e.key for e in entities}
+    assert actual_keys == expected_keys, (
+        f"Expected stable keys {expected_keys!r}, got {actual_keys!r}"
+    )
+    # None of the keys must embed the meter uuid.
+    for key in actual_keys:
+        assert meter_uuid not in key, (
+            f"Key {key!r} must NOT contain meter uuid {meter_uuid!r}"
+        )
+
+
+def test_energy_cost_toggle_survives_meter_swap(energy_db) -> None:
+    """FUE-T05 ③ (toggle stability): enabled toggle on 'energy.buy_price_now' survives meter swap.
+
+    After a meter swap the provider queries a new active meter → new identifiers[1] /
+    unique_id / topic in HA.  But the entity key stays 'energy.buy_price_now', so the
+    existing toggle row (keyed by 'energy.buy_price_now') is still found → enabled=True.
+
+    This is the critical property: the user does NOT need to re-tick toggles after a swap.
+    """
+    from app.integrations.expose import build_catalog
+    from app.models.energy import Meter
+    from app.models.expose import ExposedEntityToggle
+
+    t0 = datetime(2026, 1, 1, 0, 0, tzinfo=timezone.utc)
+    swap_at = datetime(2026, 6, 1, 0, 0, tzinfo=timezone.utc)
+
+    with Session(energy_db) as session:
+        # Old meter (initial)
+        old_meter = Meter(
+            label="Old Meter",
+            commodity="electricity",
+            started_at=t0,
+            ended_at=swap_at,
+            reason="initial",
+            note=None,
+            created_at=t0,
+        )
+        session.add(old_meter)
+        # Enable buy_price_now toggle
+        toggle = ExposedEntityToggle(
+            key="energy.buy_price_now",
+            enabled=True,
+            updated_at=t0,
+        )
+        session.add(toggle)
+        session.commit()
+
+    # Perform meter swap: new active meter
+    with Session(energy_db) as session:
+        new_meter = Meter(
+            label="New Meter",
+            commodity="electricity",
+            started_at=swap_at,
+            ended_at=None,
+            reason="meter_swap",
+            note=None,
+            created_at=swap_at,
+        )
+        session.add(new_meter)
+        session.commit()
+        new_meter_uuid = new_meter.uuid
+
+    # After swap: catalog should use new meter uuid, but toggle state is preserved.
+    with Session(energy_db) as session:
+        catalog = build_catalog(session)
+
+    buy_entry = next(
+        (e for e in catalog if e.entity.key == "energy.buy_price_now"), None
+    )
+    assert buy_entry is not None, "energy.buy_price_now must be present in catalog"
+    # identifiers[1] must now be the NEW meter's uuid
+    assert buy_entry.entity.device.identifiers[1] == new_meter_uuid, (
+        f"After swap, identifiers[1] must be new meter uuid {new_meter_uuid!r}, "
+        f"got {buy_entry.entity.device.identifiers[1]!r}"
+    )
+    # Toggle state must still be enabled (key unchanged → same toggle row found)
+    assert buy_entry.enabled is True, (
+        "energy.buy_price_now toggle must remain enabled after meter swap "
+        "(key is stable, toggle row survives)"
+    )
+
+
+def test_energy_cost_identifiers_change_after_meter_swap(energy_db) -> None:
+    """FUE-T05 ④: after meter swap, provider produces new identifiers[1] (new meter uuid).
+
+    Old uuid's entities are no longer produced → HA sensor for old uuid is frozen.
+    New uuid's entities appear → HA creates fresh sensors for the new meter.
+    """
+    from app.integrations.expose import _energy_cost_provider
+    from app.models.energy import Meter
+
+    t0 = datetime(2026, 1, 1, 0, 0, tzinfo=timezone.utc)
+    swap_at = datetime(2026, 6, 1, 0, 0, tzinfo=timezone.utc)
+
+    with Session(energy_db) as session:
+        old_meter = Meter(
+            label="Old Meter",
+            commodity="electricity",
+            started_at=t0,
+            ended_at=swap_at,
+            reason="initial",
+            note=None,
+            created_at=t0,
+        )
+        session.add(old_meter)
+        session.commit()
+        old_uuid = old_meter.uuid
+
+    # Before swap: old meter closed, new meter not yet created → no active meter → []
+    with Session(energy_db) as session:
+        result_no_active = _energy_cost_provider(session)
+    assert result_no_active == [], (
+        "Expected [] after old meter is closed but before new meter is created"
+    )
+
+    # Create new active meter (simulates the swap completing)
+    with Session(energy_db) as session:
+        new_meter = Meter(
+            label="New Meter",
+            commodity="electricity",
+            started_at=swap_at,
+            ended_at=None,
+            reason="meter_swap",
+            note=None,
+            created_at=swap_at,
+        )
+        session.add(new_meter)
+        session.commit()
+        new_uuid = new_meter.uuid
+
+    assert old_uuid != new_uuid, "Old and new meter uuids must differ"
+
+    with Session(energy_db) as session:
+        entities_after_swap = _energy_cost_provider(session)
+
+    assert len(entities_after_swap) == 6, (
+        f"Expected 6 entities after swap, got {len(entities_after_swap)}"
+    )
+    for entity in entities_after_swap:
+        assert entity.device.identifiers[1] == new_uuid, (
+            f"After swap, identifiers[1] must be new uuid {new_uuid!r}, "
+            f"got {entity.device.identifiers[1]!r}"
+        )
+        # Old uuid must not appear in identifiers
+        assert entity.device.identifiers[1] != old_uuid, (
+            f"After swap, old uuid {old_uuid!r} must not appear in identifiers"
+        )
diff --git a/tests/test_expose_catalog.py b/tests/test_expose_catalog.py
index fb6a7a8..4f27aa6 100644
--- a/tests/test_expose_catalog.py
+++ b/tests/test_expose_catalog.py
@@ -205,27 +205,58 @@ def test_register_provider_direct_call():
 def test_build_catalog_empty_with_no_devices(expose_db):
     """build_catalog with no enabled modbus devices must contain no modbus entities.
 
-    The energy_cost provider is always registered and always produces its 6 entities
-    (4 original + 2 daily) regardless of device state, so the catalog will not be empty.
-    This test checks that no *modbus* entities are present when there are no enabled
-    modbus devices.
+    FUE-T05: the energy_cost provider now requires an active electricity meter.
+    Without one, it returns [] and the catalog contains no energy entities.
+    With one, it produces 6 entities.
+
+    This test verifies both cases:
+    1. No modbus devices → no modbus entities.
+    2. No active meter → no energy entities (provider returns []).
+    3. After inserting an active meter → 6 energy entities present.
     """
     from app.integrations.expose import build_catalog
 
+    # Case: no modbus devices, no active meter → catalog is empty.
     with Session(expose_db) as session:
         catalog = build_catalog(session)
 
-    # The modbus provider finds no enabled devices → no modbus entities.
-    # The energy_cost provider always produces 6 entities, so the catalog is non-empty.
     modbus_entities = [e for e in catalog if e.entity.key.startswith("modbus.")]
     assert modbus_entities == [], (
         "Expected no modbus entities when no modbus devices are enabled"
     )
 
-    # The 6 energy_cost entities should always be present (4 original + 2 daily).
-    energy_keys = {e.entity.key for e in catalog if e.entity.key.startswith("energy.")}
-    assert len(energy_keys) == 6, (
-        f"Expected exactly 6 energy_cost entities (4 original + 2 daily), got {energy_keys!r}"
+    # No active electricity meter → energy-cost provider returns [] → no energy entities.
+    energy_keys_no_meter = {e.entity.key for e in catalog if e.entity.key.startswith("energy.")}
+    assert len(energy_keys_no_meter) == 0, (
+        f"Expected 0 energy_cost entities (no active meter), got {energy_keys_no_meter!r}"
+    )
+
+    # Insert an active electricity meter → provider should now produce 6 entities.
+    from datetime import datetime, timezone
+    now = datetime.now(tz=timezone.utc)
+    with Session(expose_db) as session:
+        from app.models.energy import Meter
+        m = Meter(
+            label="Test Meter for catalog",
+            commodity="electricity",
+            started_at=now,
+            ended_at=None,
+            reason="initial",
+            note=None,
+            created_at=now,
+        )
+        session.add(m)
+        session.commit()
+
+    with Session(expose_db) as session:
+        catalog_with_meter = build_catalog(session)
+
+    energy_keys_with_meter = {
+        e.entity.key for e in catalog_with_meter if e.entity.key.startswith("energy.")
+    }
+    assert len(energy_keys_with_meter) == 6, (
+        f"Expected exactly 6 energy_cost entities (4 original + 2 daily) with active meter, "
+        f"got {energy_keys_with_meter!r}"
     )