diff --git a/tests/test_air_dresser_tp1_21_capabilities.py b/tests/test_air_dresser_tp1_21_capabilities.py
index d6fe379..5258b58 100644
--- a/tests/test_air_dresser_tp1_21_capabilities.py
+++ b/tests/test_air_dresser_tp1_21_capabilities.py
@@ -13,6 +13,7 @@ raw code until a reporter can map codes to names in the SmartThings app.
 from custom_components.localthings.registry.adapter import flatten
 from custom_components.localthings.registry.by_type import air_dresser, for_device_by_model
 from custom_components.localthings.registry.discovery import discover
+from custom_components.localthings.registry.entities import SelectDesc, SwitchDesc
 from tests.conftest import _load_device
 
 
@@ -53,9 +54,12 @@ def test_buzzer_sound_present_and_writable():
     desc = next(
         e
         for e in air_dresser.REGISTRY.capabilities["/buzzersound/vs/0"][0].entities
-        if e.key == "buzzer_sound"
+        if e.key == "buzzer_sound" and isinstance(e, SelectDesc)
     )
-    path, body = desc.write_fn("Off", {})
+    assert desc.write_fn is not None
+    result = desc.write_fn("Off", {})
+    assert result is not None
+    path, body = result
     assert path == ["buzzersound", "vs", "0"]
     assert body == {"setBuzzerSound": "Off"}
 
@@ -75,8 +79,11 @@ def test_sanitize_present_and_toggles():
     desc = next(
         e
         for e in air_dresser.REGISTRY.capabilities["/airdresseroption/sanitize/vs/0"][0].entities
-        if e.key == "sanitize"
+        if e.key == "sanitize" and isinstance(e, SwitchDesc)
     )
-    path, body = desc.write_fn("On", {})
+    assert desc.write_fn is not None
+    result = desc.write_fn("On", {})
+    assert result is not None
+    path, body = result
     assert path == ["airdresseroption", "sanitize", "vs", "0"]
     assert body == {"x.com.samsung.da.sanitize": "On"}
diff --git a/tests/test_air_dresser_tp2_20_capabilities.py b/tests/test_air_dresser_tp2_20_capabilities.py
index 3fc9406..3ff9546 100644
--- a/tests/test_air_dresser_tp2_20_capabilities.py
+++ b/tests/test_air_dresser_tp2_20_capabilities.py
@@ -11,6 +11,7 @@ capability #162's dump doesn't report at all.
 from custom_components.localthings.registry.adapter import flatten
 from custom_components.localthings.registry.by_type import air_dresser, for_device_by_model
 from custom_components.localthings.registry.discovery import discover
+from custom_components.localthings.registry.entities import SwitchDesc
 from tests.conftest import _load_device
 
 
@@ -77,9 +78,12 @@ def test_sanitize_present_and_toggles():
     desc = next(
         e
         for e in air_dresser.REGISTRY.capabilities["/airdresseroption/sanitize/vs/0"][0].entities
-        if e.key == "sanitize"
+        if e.key == "sanitize" and isinstance(e, SwitchDesc)
     )
-    path, body = desc.write_fn("On", {})
+    assert desc.write_fn is not None
+    result = desc.write_fn("On", {})
+    assert result is not None
+    path, body = result
     assert path == ["airdresseroption", "sanitize", "vs", "0"]
     assert body == {"x.com.samsung.da.sanitize": "On"}
     assert desc.write_fn("Sparkle", {}) is None
diff --git a/tests/test_airconditioner_artik051_krac.py b/tests/test_airconditioner_artik051_krac.py
index 5862b68..6081e78 100644
--- a/tests/test_airconditioner_artik051_krac.py
+++ b/tests/test_airconditioner_artik051_krac.py
@@ -19,9 +19,10 @@ the same model with a slightly different token set (no ``Spi``,
 gating handles the same way it handles newer boards.
 """
 
-from typing import ClassVar
+from typing import ClassVar, cast
 
 from custom_components.localthings.climate import LocalThingsClimate
+from custom_components.localthings.coordinator import LocalThingsCoordinator
 from custom_components.localthings.registry.adapter import flatten
 from custom_components.localthings.registry.by_type import (
     airconditioner,
@@ -82,7 +83,7 @@ def _climate(resources, coordinator=None):
     bound, _ = _discover(resources)
     climate_bound = next(item for item in bound if isinstance(item.desc, ClimateDesc))
     return LocalThingsClimate(
-        coordinator or _FakeCoordinator(resources),
+        cast(LocalThingsCoordinator, coordinator or _FakeCoordinator(resources)),
         climate_bound,
     )
 
diff --git a/tests/test_airconditioner_capabilities.py b/tests/test_airconditioner_capabilities.py
index 64dfef9..fe3c08f 100644
--- a/tests/test_airconditioner_capabilities.py
+++ b/tests/test_airconditioner_capabilities.py
@@ -10,7 +10,12 @@ from custom_components.localthings.registry.adapter import flatten
 from custom_components.localthings.registry.by_type import for_device_by_model
 from custom_components.localthings.registry.capabilities import airconditioner
 from custom_components.localthings.registry.discovery import discover
-from custom_components.localthings.registry.entities import ClimateDesc, SelectDesc
+from custom_components.localthings.registry.entities import (
+    ClimateDesc,
+    SelectDesc,
+    SensorDesc,
+    SwitchDesc,
+)
 from tests.conftest import _load_device
 
 
@@ -103,7 +108,9 @@ def test_climate_write_targets():
     /power/0 is absent on most boards and a non-authoritative mirror where
     present; /temperature/desired/0 is only written via the temperature_ocf
     kind, on boards that have the OCF pair)."""
-    write = airconditioner.CLIMATE.entities[0].write_fn
+    climate_desc = next(e for e in airconditioner.CLIMATE.entities if isinstance(e, ClimateDesc))
+    assert climate_desc.write_fn is not None
+    write = climate_desc.write_fn
     assert write(("power", True), {}) == (["power", "vs", "0"], {"x.com.samsung.da.power": "On"})
     assert write(("power", False), {}) == (["power", "vs", "0"], {"x.com.samsung.da.power": "Off"})
     assert write(("mode", "Heat"), {}) == (
@@ -285,13 +292,17 @@ def test_caww_tp2_sac_installationinfo_is_ignored():
 
 
 def test_mute_once_write_target():
-    write = airconditioner.MUTE_ONCE.entities[0].write_fn
+    desc = next(e for e in airconditioner.MUTE_ONCE.entities if isinstance(e, SwitchDesc))
+    assert desc.write_fn is not None
+    write = desc.write_fn
     assert write("On", {}) == (["option", "muteonce", "vs", "0"], {"muteonce": "On"})
     assert write("Off", {}) == (["option", "muteonce", "vs", "0"], {"muteonce": "Off"})
 
 
 def test_display_light_write_target():
-    write = airconditioner.DISPLAY_LIGHT.entities[0].write_fn
+    desc = next(e for e in airconditioner.DISPLAY_LIGHT.entities if isinstance(e, SwitchDesc))
+    assert desc.write_fn is not None
+    write = desc.write_fn
     assert write("On", {}) == (["light", "vs", "0"], {"mode": "On"})
     assert write("Off", {}) == (["light", "vs", "0"], {"mode": "Off"})
 
@@ -375,7 +386,12 @@ def test_display_light_option_parsing_and_gating():
 def test_mode_options_display_light_write_is_inverted_single_token():
     """Turning the lamp ON writes the inverted 'Light_Off' token as a
     single-element options list (single-token merge); OFF writes 'Light_On'."""
-    sw = next(e for e in airconditioner.CLIMATE.entities if e.key == "display_light")
+    sw = next(
+        e
+        for e in airconditioner.CLIMATE.entities
+        if e.key == "display_light" and isinstance(e, SwitchDesc)
+    )
+    assert sw.write_fn is not None
     assert sw.write_fn("On", {}) == (
         ["mode", "vs", "0"],
         {"x.com.samsung.da.options": ["Light_Off"]},
@@ -433,12 +449,14 @@ def test_current_temperature_vs_only_binds_when_ocf_href_absent():
     CURRENT_TEMPERATURE when a device (like this one) reports both
     /temperature/current/0 and /temperatures/vs/0."""
     match = airconditioner.CURRENT_TEMPERATURE_VS.match_fn
+    assert match is not None
     assert match({}, {"/temperature/current/0": {}}) is False
     assert match({}, {}) is True
 
 
 def test_humidity_reads_five_percent_field_not_stuck_humidity_field():
     desc = airconditioner.HUMIDITY.entities[0]
+    assert desc.rep_fn is not None
     rep = {"x.com.samsung.da.humidity": "0", "x.com.samsung.da.fivepercentHumidity": "42"}
     assert desc.rep_fn(rep) == 42.0
 
@@ -448,6 +466,7 @@ def test_humidity_falls_back_to_the_plain_field_where_five_percent_is_absent():
     Their plain field is not stuck -- it carries a reading while Air monitoring
     is on -- so 0 means "not measuring" on both generations, not 0% humidity."""
     desc = airconditioner.HUMIDITY.entities[0]
+    assert desc.rep_fn is not None
     assert desc.rep_fn({"x.com.samsung.da.humidity": "51"}) == 51.0
     assert desc.rep_fn({"x.com.samsung.da.humidity": "0"}) is None
     assert desc.rep_fn({}) is None
@@ -461,6 +480,7 @@ def test_humidity_five_percent_field_passes_a_genuine_zero_through():
     fallback field collapses 0 -- fivepercentHumidity's 0 is a real
     reading."""
     desc = airconditioner.HUMIDITY.entities[0]
+    assert desc.rep_fn is not None
     assert desc.rep_fn({"x.com.samsung.da.fivepercentHumidity": "0"}) == 0.0
 
 
@@ -580,21 +600,25 @@ def test_lnx_rac_heatpump_enable_switches_are_writable():
 
 
 def test_lnx_rac_heatpump_absence_power_saving_write_target():
-    write = next(
+    desc = next(
         e
         for e in airconditioner.ABSENCE_POWER_SAVING.entities
-        if e.key == "absence_power_saving_active"
-    ).write_fn
+        if e.key == "absence_power_saving_active" and isinstance(e, SwitchDesc)
+    )
+    assert desc.write_fn is not None
+    write = desc.write_fn
     assert write("On", {}) == (["mds", "absencepowersaving", "vs", "0"], {"status": "On"})
     assert write("Off", {}) == (["mds", "absencepowersaving", "vs", "0"], {"status": "Off"})
 
 
 def test_lnx_rac_heatpump_motion_detect_wind_write_target():
-    write = next(
+    desc = next(
         e
         for e in airconditioner.MOTION_DETECT_WIND.entities
-        if e.key == "motion_detect_wind_active"
-    ).write_fn
+        if e.key == "motion_detect_wind_active" and isinstance(e, SwitchDesc)
+    )
+    assert desc.write_fn is not None
+    write = desc.write_fn
     assert write("On", {}) == (
         ["option", "motiondetectwind", "stateful", "vs", "0"],
         {"status": "On"},
@@ -710,6 +734,7 @@ def test_tropical_night_absent_when_no_sleep_token():
     reg = for_device_by_model(
         info["x.com.samsung.da.modelNum"], info["x.com.samsung.da.description"]
     )
+    assert reg is not None
     state = flatten(discover(resources, reg.capabilities, reg.pattern_capabilities), resources)
     assert "tropical_night_mode" not in state
 
@@ -723,6 +748,7 @@ def test_tropical_night_state_levels_across_fixtures():
         r = for_device_by_model(
             info["x.com.samsung.da.modelNum"], info["x.com.samsung.da.description"]
         )
+        assert r is not None
         return flatten(discover(res, r.capabilities, r.pattern_capabilities), res).get(
             "tropical_night_mode"
         )
@@ -736,13 +762,18 @@ def test_air_filter_usage_hours_reads_raw_count():
     """filterUsage is a lifetime hour counter (41 of 500) that resets on
     filter replacement -- total_increasing, not measurement. Unit comes from
     filterCapacityUnit via unit_fn, not a hardcoded 'h'."""
-    desc = next(e for e in airconditioner.AIR_FILTER.entities if e.key == "air_filter_usage_hours")
+    desc = next(
+        e
+        for e in airconditioner.AIR_FILTER.entities
+        if e.key == "air_filter_usage_hours" and isinstance(e, SensorDesc)
+    )
     assert desc.value_fn("41") == 41
     assert desc.value_fn(41) == 41
     assert desc.value_fn(None) is None
     assert desc.value_fn("not-a-number") is None
     assert desc.device_class == "duration"
     assert desc.state_class == "total_increasing"
+    assert desc.unit_fn is not None
     assert desc.unit_fn({"x.com.samsung.da.filterCapacityUnit": "Hour"}) == "h"
     assert desc.unit_fn({"x.com.samsung.da.filterCapacityUnit": "Minute"}) == "min"
     assert desc.unit_fn({}) == "h"  # static fallback when the field is absent
@@ -758,6 +789,7 @@ def test_air_filter_threshold_is_writable_select():
     desc = next(e for e in airconditioner.AIR_FILTER.entities if e.key == "air_filter_threshold")
     assert isinstance(desc, SelectDesc)
     assert desc.options_field == "x.com.samsung.da.supportedFilterDesiredUsage"
+    assert desc.exists_fn is not None
     assert (
         desc.exists_fn(
             {"x.com.samsung.da.supportedFilterDesiredUsage": ["180", "300", "500", "700"]}, {}
@@ -770,6 +802,7 @@ def test_air_filter_threshold_is_writable_select():
     assert desc.value_fn(500) == "500"
     assert desc.value_fn(None) is None
     # Write POSTs the selected option as the scalar field.
+    assert desc.write_fn is not None
     assert desc.write_fn("700", {}) == (
         ["filter", "airdustfilter", "vs", "0"],
         {"x.com.samsung.da.filterDesiredUsage": "700"},
diff --git a/tests/test_airconditioner_tp1x_rac_01001_fan.py b/tests/test_airconditioner_tp1x_rac_01001_fan.py
index 414ccfd..575ee38 100644
--- a/tests/test_airconditioner_tp1x_rac_01001_fan.py
+++ b/tests/test_airconditioner_tp1x_rac_01001_fan.py
@@ -11,13 +11,14 @@ any code _DEVICE_TO_FAN doesn't already cover, instead of hardcoding a
 second numeric scale.
 """
 
-from typing import ClassVar
+from typing import ClassVar, cast
 
 from custom_components.localthings.climate import (
     _DEVICE_TO_FAN,
     LocalThingsClimate,
     _wind_strength_label,
 )
+from custom_components.localthings.coordinator import LocalThingsCoordinator
 from custom_components.localthings.registry import by_type
 from custom_components.localthings.registry.discovery import discover
 from custom_components.localthings.registry.entities import ClimateDesc
@@ -53,9 +54,12 @@ def _climate(resources, coordinator=None):
     reg = by_type.for_device_by_model(
         info["x.com.samsung.da.modelNum"], info["x.com.samsung.da.description"]
     )
+    assert reg is not None
     bound = discover(resources, reg.capabilities, reg.pattern_capabilities)
     climate_bound = next(item for item in bound if isinstance(item.desc, ClimateDesc))
-    return LocalThingsClimate(coordinator or _FakeCoordinator(resources), climate_bound)
+    return LocalThingsClimate(
+        cast(LocalThingsCoordinator, coordinator or _FakeCoordinator(resources)), climate_bound
+    )
 
 
 def test_wind_strength_label_reads_the_devices_own_modes_name():
diff --git a/tests/test_by_type.py b/tests/test_by_type.py
index 2bf6931..716af72 100644
--- a/tests/test_by_type.py
+++ b/tests/test_by_type.py
@@ -1,5 +1,7 @@
 """Tests for samsung_appliance/registry/by_type."""
 
+from typing import cast
+
 import pytest
 
 from custom_components.localthings.registry.by_type import (
@@ -110,7 +112,10 @@ class TestBoardTokens:
         from custom_components.localthings.registry.by_type import _board_tokens
 
         assert _board_tokens("", "|") == []
-        assert _board_tokens(None, "|") == []
+        # value is annotated `str`, but the implementation is defensive
+        # against a caller passing a genuinely missing modelNum/description
+        # (see the `value or ""` in _board_tokens) -- exercise that directly.
+        assert _board_tokens(cast(str, None), "|") == []
 
 
 class TestBoardTokenTable:
diff --git a/tests/test_capability.py b/tests/test_capability.py
index 1cd9ac3..bef599e 100644
--- a/tests/test_capability.py
+++ b/tests/test_capability.py
@@ -14,7 +14,7 @@ def test_capability_defaults():
 def test_capability_is_frozen():
     c = Capability(href="/kidslock/vs/0", entities=())
     try:
-        c.href = "/other/vs/0"
+        setattr(c, "href", "/other/vs/0")
     except Exception:
         return
     raise AssertionError("expected frozen dataclass")
diff --git a/tests/test_common_capabilities.py b/tests/test_common_capabilities.py
index 2a2a2c7..4b6609f 100644
--- a/tests/test_common_capabilities.py
+++ b/tests/test_common_capabilities.py
@@ -135,13 +135,19 @@ class TestPowerFallback:
         desc = next(e for e in common.POWER_GENERIC.entities if isinstance(e, SwitchDesc))
         assert desc.value_fn(True) is True
         assert desc.value_fn(False) is False
-        path, body = desc.write_fn("On", {})
+        assert desc.write_fn is not None
+        result = desc.write_fn("On", {})
+        assert result is not None
+        path, body = result
         assert path == ["power", "0"]
         assert body == {"value": True}
-        assert desc.write_fn("Off", {})[1] == {"value": False}
+        off_result = desc.write_fn("Off", {})
+        assert off_result is not None
+        assert off_result[1] == {"value": False}
 
     def test_vs_fallback_binds_only_when_generic_absent(self):
         assert common.POWER_VS_FALLBACK.href == "/power/vs/0"
+        assert common.POWER_VS_FALLBACK.match_fn is not None
         assert common.POWER_VS_FALLBACK.match_fn({}, {"/power/vs/0": {}}) is True
         assert common.POWER_VS_FALLBACK.match_fn({}, {"/power/0": {}, "/power/vs/0": {}}) is False
 
@@ -149,7 +155,10 @@ class TestPowerFallback:
         desc = next(e for e in common.POWER_VS_FALLBACK.entities if isinstance(e, SwitchDesc))
         assert desc.value_fn("On") is True
         assert desc.value_fn("Off") is False
-        path, body = desc.write_fn("On", {})
+        assert desc.write_fn is not None
+        result = desc.write_fn("On", {})
+        assert result is not None
+        path, body = result
         assert path == ["power", "vs", "0"]
         assert body == {"x.com.samsung.da.power": "On"}
 
@@ -160,6 +169,8 @@ class TestPowerFallback:
             "/power/0": {"value": True},
             "/wm/setinfo/vs/0": {"x.com.samsung.da.isModelSettingPowerOnOff": "false"},
         }
+        assert switch.exists_fn is not None
+        assert sensor.exists_fn is not None
         assert switch.exists_fn(resources["/power/0"], resources) is False
         assert sensor.exists_fn(resources["/power/0"], resources) is True
 
@@ -170,6 +181,8 @@ class TestPowerFallback:
             "/power/0": {"value": True},
             "/wm/setinfo/vs/0": {"x.com.samsung.da.isModelSettingPowerOnOff": "true"},
         }
+        assert switch.exists_fn is not None
+        assert sensor.exists_fn is not None
         assert switch.exists_fn(resources["/power/0"], resources) is True
         assert sensor.exists_fn(resources["/power/0"], resources) is False
 
@@ -177,6 +190,8 @@ class TestPowerFallback:
         switch = next(e for e in common.POWER_GENERIC.entities if isinstance(e, SwitchDesc))
         sensor = next(e for e in common.POWER_GENERIC.entities if isinstance(e, BinarySensorDesc))
         resources = {"/power/0": {"value": True}}
+        assert switch.exists_fn is not None
+        assert sensor.exists_fn is not None
         assert switch.exists_fn(resources["/power/0"], resources) is True
         assert sensor.exists_fn(resources["/power/0"], resources) is False
 
@@ -291,6 +306,7 @@ class TestKidsLockFallback:
         assert desc.value_fn(True) is False  # value=True -> Off=Locked
 
     def test_vs_fallback_gated(self):
+        assert common.KIDS_LOCK_VS_FALLBACK.match_fn is not None
         assert common.KIDS_LOCK_VS_FALLBACK.match_fn({}, {"/kidslock/vs/0": {}}) is True
         assert (
             common.KIDS_LOCK_VS_FALLBACK.match_fn({}, {"/kidslock/0": {}, "/kidslock/vs/0": {}})
@@ -316,6 +332,7 @@ class TestRemoteControlFallback:
         assert desc.value_fn(False) is False
 
     def test_vs_fallback_gated(self):
+        assert common.REMOTE_CONTROL_VS_FALLBACK.match_fn is not None
         assert common.REMOTE_CONTROL_VS_FALLBACK.match_fn({}, {"/remotectrl/vs/0": {}}) is True
         assert (
             common.REMOTE_CONTROL_VS_FALLBACK.match_fn(
@@ -351,18 +368,22 @@ class TestEnergyMeter:
 
     def test_power_watts_hidden_for_dead_sentinel(self):
         pw = next(e for e in common.ENERGY_METER.entities if e.key == "power_watts")
+        assert pw.exists_fn is not None
         assert pw.exists_fn({"x.com.samsung.da.instantaneousPower": "-500"}, {}) is False
 
     def test_power_watts_shown_for_real_value(self):
         pw = next(e for e in common.ENERGY_METER.entities if e.key == "power_watts")
+        assert pw.exists_fn is not None
         assert pw.exists_fn({"x.com.samsung.da.instantaneousPower": "150"}, {}) is True
 
     def test_energy_kwh_hidden_when_cumulative_power_absent(self):
         kwh = next(e for e in common.ENERGY_METER.entities if e.key == "energy_kwh")
+        assert kwh.exists_fn is not None
         assert kwh.exists_fn({"x.com.samsung.da.instantaneousPower": "-500"}, {}) is False
 
     def test_energy_kwh_shown_when_present(self):
         kwh = next(e for e in common.ENERGY_METER.entities if e.key == "energy_kwh")
+        assert kwh.exists_fn is not None
         assert kwh.exists_fn({"x.com.samsung.da.cumulativePower": "58900"}, {}) is True
 
     def test_both_entities_included_on_true_stub(self):
@@ -371,6 +392,8 @@ class TestEnergyMeter:
         but data isn't fetched yet; include both so sub-polls populate them."""
         pw = next(e for e in common.ENERGY_METER.entities if e.key == "power_watts")
         kwh = next(e for e in common.ENERGY_METER.entities if e.key == "energy_kwh")
+        assert pw.exists_fn is not None
+        assert kwh.exists_fn is not None
         stub = {"href": "/energy/consumption/vs/0"}
         assert pw.exists_fn(stub, {}) is True
         assert kwh.exists_fn(stub, {}) is True
@@ -381,6 +404,8 @@ class TestEnergyMeter:
         resource doesn't get a phantom always-"unknown" entity (issue #127)."""
         pw = next(e for e in common.ENERGY_METER.entities if e.key == "power_watts")
         kwh = next(e for e in common.ENERGY_METER.entities if e.key == "energy_kwh")
+        assert pw.exists_fn is not None
+        assert kwh.exists_fn is not None
         assert pw.exists_fn({}, {}) is False
         assert kwh.exists_fn({}, {}) is False
 
@@ -388,6 +413,7 @@ class TestEnergyMeter:
         """A populated rep that lacks instantaneousPower must not spawn a
         phantom power sensor (the exists_fn replaces the field-presence gate)."""
         pw = next(e for e in common.ENERGY_METER.entities if e.key == "power_watts")
+        assert pw.exists_fn is not None
         assert pw.exists_fn({"x.com.samsung.da.cumulativePower": "5"}, {}) is False
 
 
diff --git a/tests/test_coordinator_send_command.py b/tests/test_coordinator_send_command.py
index dc26cca..2b9b04a 100644
--- a/tests/test_coordinator_send_command.py
+++ b/tests/test_coordinator_send_command.py
@@ -14,12 +14,14 @@ only the minimal body over the wire.
 
 from __future__ import annotations
 
+from typing import cast
 from unittest.mock import AsyncMock
 
 import cbor2
 import pytest
 from homeassistant.core import HomeAssistant
 from pytest_homeassistant_custom_component.common import MockConfigEntry
+from smartthings_local.protocol.dtls_session import DtlsCoapSession
 
 from custom_components.localthings.const import (
     CONF_HOST,
@@ -31,6 +33,7 @@ from custom_components.localthings.const import (
 from custom_components.localthings.coordinator import LocalThingsCoordinator
 from custom_components.localthings.registry.capabilities import laundry
 from custom_components.localthings.registry.capabilities.airconditioner import _climate_write
+from custom_components.localthings.registry.capability import Capability
 from custom_components.localthings.registry.discovery import BoundEntity
 from custom_components.localthings.registry.entities import ClimateDesc
 from custom_components.localthings.registry.subdevices import Subdevice
@@ -65,7 +68,7 @@ def coordinator(hass: HomeAssistant) -> LocalThingsCoordinator:
     entry.add_to_hass(hass)
     coord = LocalThingsCoordinator(hass, entry)
     coord.async_request_refresh = AsyncMock()
-    coord._session = _FakeSendSession()
+    coord._session = cast(DtlsCoapSession, _FakeSendSession())
     return coord
 
 
@@ -80,7 +83,7 @@ async def test_options_write_posts_only_the_changed_token(coordinator) -> None:
     )
 
     desc = laundry.cycle_select(translation_key="dryer_cycle", icon="x")
-    bound = BoundEntity(href=href, capability=None, desc=desc)
+    bound = BoundEntity(href=href, capability=Capability(), desc=desc)
 
     await coordinator.async_send_command(bound, "1D")
 
@@ -102,7 +105,7 @@ async def test_options_write_optimistic_cache_keeps_sibling_tokens(coordinator)
     )
 
     desc = laundry.cycle_select(translation_key="dryer_cycle", icon="x")
-    bound = BoundEntity(href=href, capability=None, desc=desc)
+    bound = BoundEntity(href=href, capability=Capability(), desc=desc)
 
     await coordinator.async_send_command(bound, "1D")
 
@@ -127,7 +130,7 @@ async def test_options_write_optimistic_cache_keeps_sibling_tokens(coordinator)
 
 def _climate_bound(href: str, subdevice: Subdevice) -> BoundEntity:
     desc = ClimateDesc(key="climate", translation_key="airconditioner", write_fn=_climate_write)
-    return BoundEntity(href=href, capability=None, desc=desc, subdevice=subdevice)
+    return BoundEntity(href=href, capability=Capability(), desc=desc, subdevice=subdevice)
 
 
 async def test_indexed_subdevice_write_posts_to_translated_path(coordinator) -> None:
diff --git a/tests/test_dryer_capabilities.py b/tests/test_dryer_capabilities.py
index 229ff87..e82fd23 100644
--- a/tests/test_dryer_capabilities.py
+++ b/tests/test_dryer_capabilities.py
@@ -4,6 +4,7 @@ from custom_components.localthings.registry.adapter import flatten
 from custom_components.localthings.registry.by_type import for_device_by_model
 from custom_components.localthings.registry.capabilities import dryer, ignored, laundry
 from custom_components.localthings.registry.discovery import discover
+from custom_components.localthings.registry.entities import SelectDesc
 from tests.conftest import _load_device
 
 
@@ -74,13 +75,14 @@ def test_course_bound_to_shared_course_vs_0():
     the shipped dryer_cycle_table_03 translations, consistent with
     washer/dishwasher."""
     assert dryer.DRYER_COURSE.href == "/course/vs/0"
-    desc = next(e for e in dryer.DRYER_COURSE.entities if e.key == "cycle")
+    desc = next(e for e in dryer.DRYER_COURSE.entities if e.key == "cycle" and isinstance(e, SelectDesc))
     assert callable(desc.translation_key)
     table_03 = {"/st/dryercourse/vs/0": {"x.com.samsung.da.st.courseTable": "Table_03"}}
     assert desc.translation_key(table_03) == "dryer_cycle_table_03"
     assert desc.translation_key({}) == "cycle"
     assert desc.options is laundry.cycle_options
     rep = {"x.com.samsung.da.options": ["Course_16", "GMT_02"]}
+    assert desc.rep_fn is not None
     assert desc.rep_fn(rep) == "16"
 
 
diff --git a/tests/test_entity_naming.py b/tests/test_entity_naming.py
index 1153091..74b95ed 100644
--- a/tests/test_entity_naming.py
+++ b/tests/test_entity_naming.py
@@ -1,5 +1,8 @@
 """Tests for translated entity naming and dynamic instance placeholders."""
 
+from typing import cast
+
+from custom_components.localthings.coordinator import LocalThingsCoordinator
 from custom_components.localthings.entity import LocalThingsEntity
 from custom_components.localthings.registry.capability import Capability
 from custom_components.localthings.registry.discovery import BoundEntity
@@ -23,7 +26,7 @@ def _make_entity(desc, href="/x/vs/0", key_override=None, instance="", instance_
         key_override=key_override,
         instance_name=instance_name,
     )
-    return LocalThingsEntity(_FakeCoordinator(), bound)
+    return LocalThingsEntity(cast(LocalThingsCoordinator, _FakeCoordinator()), bound)
 
 
 def test_descriptor_key_is_the_default_translation_key():
diff --git a/tests/test_fridge_capabilities.py b/tests/test_fridge_capabilities.py
index 830fbaa..3d755ae 100644
--- a/tests/test_fridge_capabilities.py
+++ b/tests/test_fridge_capabilities.py
@@ -1,8 +1,15 @@
 """Tests for fridge-specific capabilities."""
 
-from typing import ClassVar
+from collections.abc import Callable
+from typing import ClassVar, cast
 
+from custom_components.localthings.coordinator import LocalThingsCoordinator
 from custom_components.localthings.registry.capabilities import fridge
+from custom_components.localthings.registry.entities import (
+    NumberDesc,
+    SelectDesc,
+    SensorDesc,
+)
 
 
 class TestTempCurrentGeneric:
@@ -11,15 +18,18 @@ class TestTempCurrentGeneric:
     resource in Celsius."""
 
     def test_unit_reads_celsius(self):
-        desc = fridge.TEMP_CURRENT_GENERIC.entities[0]
+        desc = next(e for e in fridge.TEMP_CURRENT_GENERIC.entities if isinstance(e, SensorDesc))
+        assert desc.unit_fn is not None
         assert desc.unit_fn({"temperature": 3.0, "units": "C"}) == "°C"
 
     def test_unit_reads_fahrenheit(self):
-        desc = fridge.TEMP_CURRENT_GENERIC.entities[0]
+        desc = next(e for e in fridge.TEMP_CURRENT_GENERIC.entities if isinstance(e, SensorDesc))
+        assert desc.unit_fn is not None
         assert desc.unit_fn({"temperature": 5.0, "units": "F"}) == "°F"
 
     def test_unit_defaults_to_fahrenheit_when_missing(self):
-        desc = fridge.TEMP_CURRENT_GENERIC.entities[0]
+        desc = next(e for e in fridge.TEMP_CURRENT_GENERIC.entities if isinstance(e, SensorDesc))
+        assert desc.unit_fn is not None
         assert desc.unit_fn({"temperature": 5.0}) == "°F"
 
 
@@ -32,23 +42,27 @@ class TestDoorGeneric:
 
     def test_reads_bare_open_state(self):
         desc = fridge.DOOR_GENERIC.entities[0]
+        assert desc.rep_fn is not None
         assert desc.rep_fn({"openState": "Open"}) is True
         assert desc.rep_fn({"openState": "Close"}) is False
 
     def test_reads_vendor_prefixed_open_state(self):
         desc = fridge.DOOR_GENERIC.entities[0]
+        assert desc.rep_fn is not None
         assert desc.rep_fn({"x.com.samsung.da.openState": "Open"}) is True
         assert desc.rep_fn({"x.com.samsung.da.openState": "Close"}) is False
 
     def test_prefers_bare_field_when_both_present(self):
         desc = fridge.DOOR_GENERIC.entities[0]
+        assert desc.rep_fn is not None
         rep = {"openState": "Open", "x.com.samsung.da.openState": "Close"}
         assert desc.rep_fn(rep) is True
 
 
 class TestTempSetpointGeneric:
     def test_unit_reads_celsius(self):
-        desc = fridge.TEMP_SETPOINT.entities[0]
+        desc = next(e for e in fridge.TEMP_SETPOINT.entities if isinstance(e, NumberDesc))
+        assert desc.unit_fn is not None
         assert desc.unit_fn({"temperature": -19.0, "units": "C"}) == "°C"
 
 
@@ -58,8 +72,11 @@ class TestTemperaturesFallback:
 
     def test_freezer_unit_celsius(self):
         desc = next(
-            e for e in fridge.TEMPERATURES_FALLBACK.entities if e.key == "freezer_temperature"
+            e
+            for e in fridge.TEMPERATURES_FALLBACK.entities
+            if e.key == "freezer_temperature" and isinstance(e, SensorDesc)
         )
+        assert desc.unit_fn is not None
         rep = {
             "x.com.samsung.da.items": [
                 {
@@ -79,8 +96,11 @@ class TestTemperaturesFallback:
 
     def test_fridge_unit_fahrenheit(self):
         desc = next(
-            e for e in fridge.TEMPERATURES_FALLBACK.entities if e.key == "fridge_temperature"
+            e
+            for e in fridge.TEMPERATURES_FALLBACK.entities
+            if e.key == "fridge_temperature" and isinstance(e, SensorDesc)
         )
+        assert desc.unit_fn is not None
         rep = {
             "x.com.samsung.da.items": [
                 {
@@ -94,8 +114,11 @@ class TestTemperaturesFallback:
 
     def test_unit_defaults_to_fahrenheit_when_item_missing(self):
         desc = next(
-            e for e in fridge.TEMPERATURES_FALLBACK.entities if e.key == "freezer_temperature"
+            e
+            for e in fridge.TEMPERATURES_FALLBACK.entities
+            if e.key == "freezer_temperature" and isinstance(e, SensorDesc)
         )
+        assert desc.unit_fn is not None
         assert desc.unit_fn({"x.com.samsung.da.items": []}) == "°F"
 
 
@@ -130,17 +153,20 @@ class TestRefrigerationFallback:
         desc = next(e for e in fridge.REFRIGERATION_FALLBACK.entities if e.key == "defrost_active")
         assert desc.value_fn(True) is True
         assert desc.value_fn(False) is False
+        assert desc.exists_fn is not None
         assert desc.exists_fn({}, {"/refrigeration/0": {}}) is True
         assert desc.exists_fn({}, {"/refrigeration/0": {}, "/defrost/block/vs/0": {}}) is False
 
     def test_rapid_switches_hidden_when_vs_href_present(self):
         for key in ("rapid_fridge", "rapid_freezing"):
             desc = next(e for e in fridge.REFRIGERATION_FALLBACK.entities if e.key == key)
+            assert desc.exists_fn is not None
             assert desc.exists_fn({}, {"/refrigeration/vs/0": {}, "/refrigeration/0": {}}) is False
 
     def test_rapid_switches_shown_when_vs_href_absent(self):
         for key in ("rapid_fridge", "rapid_freezing"):
             desc = next(e for e in fridge.REFRIGERATION_FALLBACK.entities if e.key == key)
+            assert desc.exists_fn is not None
             assert desc.exists_fn({}, {"/refrigeration/0": {}}) is True
 
 
@@ -201,6 +227,7 @@ class TestFlexZone:
             "x.com.samsung.da.supportedOptions": ["KIMCHIT_STORAGE_FREEZER_NORMAL_[0]:[0]"],
         }
         desc = fridge.FLEX_ZONE.entities[0]
+        assert desc.exists_fn is not None
         assert desc.exists_fn(no_overlap_rep, {}) is False
 
         overlap_rep = {
@@ -250,8 +277,11 @@ class TestPantryZone:
         assert fridge.PANTRY_ZONE.href == "/status/pantry/one/vs/0"
 
     def test_write(self):
-        desc = fridge.PANTRY_ZONE.entities[0]
-        path, body = desc.write_fn("FDR_WINE", {})
+        desc = next(e for e in fridge.PANTRY_ZONE.entities if isinstance(e, SelectDesc))
+        assert desc.write_fn is not None
+        result = desc.write_fn("FDR_WINE", {})
+        assert result is not None
+        path, body = result
         assert path == ["status", "pantry", "one", "vs", "0"]
         assert body == {"x.com.samsung.da.mode": "FDR_WINE"}
 
@@ -266,8 +296,13 @@ class TestDefiniteTemperatureCooler:
         assert fridge.DEFINITE_TEMPERATURE_COOLER.href == "/temperature/definite/cooler/vs/0"
 
     def test_write(self):
-        desc = fridge.DEFINITE_TEMPERATURE_COOLER.entities[0]
-        path, body = desc.write_fn("3", {})
+        desc = next(
+            e for e in fridge.DEFINITE_TEMPERATURE_COOLER.entities if isinstance(e, SelectDesc)
+        )
+        assert desc.write_fn is not None
+        result = desc.write_fn("3", {})
+        assert result is not None
+        path, body = result
         assert path == ["temperature", "definite", "cooler", "vs", "0"]
         assert body == {"x.com.samsung.da.definite.desired": "3"}
 
@@ -304,14 +339,19 @@ class TestKimchiZone:
         assert fridge.KIMCHI_DOOR_GENERIC.href_prefix == "/kimchidoors/"
 
     def test_write_derives_path_from_href(self):
-        desc = fridge.KIMCHI_ZONE.entities[0]
+        desc = next(e for e in fridge.KIMCHI_ZONE.entities if isinstance(e, SelectDesc))
+        assert desc.write_fn is not None
+        write_fn = cast("Callable[..., tuple[list[str], dict] | None]", desc.write_fn)
         rep = {"x.com.samsung.da.supportMode": ["KIMCHI_STORAGE_COLD"]}
-        path, body = desc.write_fn("KIMCHI_STORAGE_COLD", rep, href="/status/kimchi/middle/vs/0")
+        result = write_fn("KIMCHI_STORAGE_COLD", rep, href="/status/kimchi/middle/vs/0")
+        assert result is not None
+        path, body = result
         assert path == ["status", "kimchi", "middle", "vs", "0"]
         assert body == {"x.com.samsung.da.currentMode": "KIMCHI_STORAGE_COLD"}
 
     def test_write_without_href_is_rejected(self):
-        desc = fridge.KIMCHI_ZONE.entities[0]
+        desc = next(e for e in fridge.KIMCHI_ZONE.entities if isinstance(e, SelectDesc))
+        assert desc.write_fn is not None
         rep = {"x.com.samsung.da.supportMode": ["KIMCHI_STORAGE_COLD"]}
         assert desc.write_fn("KIMCHI_STORAGE_COLD", rep) is None
 
@@ -320,10 +360,12 @@ class TestKimchiZone:
         written blind -- this write path is unconfirmed against real
         hardware (module docstring above KIMCHI_ZONE), so a bad value here
         is a food-safety-adjacent outcome, not just a cosmetic one."""
-        desc = fridge.KIMCHI_ZONE.entities[0]
+        desc = next(e for e in fridge.KIMCHI_ZONE.entities if isinstance(e, SelectDesc))
+        assert desc.write_fn is not None
+        write_fn = cast("Callable[..., tuple[list[str], dict] | None]", desc.write_fn)
         rep = {"x.com.samsung.da.supportMode": ["KIMCHI_STORAGE_COLD"]}
         assert (
-            desc.write_fn(
+            write_fn(
                 "KIMCHI_STORAGE_WARM",
                 rep,
                 href="/status/kimchi/middle/vs/0",
@@ -340,6 +382,7 @@ class TestKimchiZone:
 
     def test_door_reuses_open_state_helper(self):
         desc = fridge.KIMCHI_DOOR_GENERIC.entities[0]
+        assert desc.rep_fn is not None
         assert desc.rep_fn({"x.com.samsung.da.openState": "Open"}) is True
         assert desc.rep_fn({"x.com.samsung.da.openState": "Close"}) is False
 
@@ -381,7 +424,7 @@ class TestKimchiZone:
                 self.commands.append(value)
 
         coordinator = _FakeCoordinator(resources, flatten(bound, resources))
-        entity = LocalThingsSelect(coordinator, mode_bound)
+        entity = LocalThingsSelect(cast(LocalThingsCoordinator, coordinator), mode_bound)
 
         assert entity.current_option == "kimchi_storage_normal"
         assert "kimchi_storage_cold" in entity.options
diff --git a/tests/test_microwave_capabilities.py b/tests/test_microwave_capabilities.py
index 91b2c9c..8b4e759 100644
--- a/tests/test_microwave_capabilities.py
+++ b/tests/test_microwave_capabilities.py
@@ -7,6 +7,7 @@ from custom_components.localthings.registry.by_type import (
 )
 from custom_components.localthings.registry.capabilities import microwave
 from custom_components.localthings.registry.discovery import discover
+from custom_components.localthings.registry.entities import NumberDesc, SelectDesc, SwitchDesc
 
 # ---------------------------------------------------------------------------
 # Device-type detection + full-dump coverage
@@ -76,16 +77,23 @@ def test_qooker_fixture_resolves_as_microwave_and_has_no_unbound_hrefs():
 # ---------------------------------------------------------------------------
 
 
+def _microwave_setpoint_desc():
+    return next(e for e in microwave.MICROWAVE_SETPOINT.entities if isinstance(e, NumberDesc))
+
+
 def test_microwave_setpoint_write_is_read_modify_write():
-    desc = microwave.MICROWAVE_SETPOINT.entities[0]
+    desc = _microwave_setpoint_desc()
     rep = {"x.com.samsung.da.items": [{"x.com.samsung.da.desired": "0"}]}
-    path, body = desc.write_fn(180, rep)
+    assert desc.write_fn is not None
+    result = desc.write_fn(180, rep)
+    assert result is not None
+    path, body = result
     assert path == ["temperatures", "vs", "0"]
     assert body["x.com.samsung.da.items"][0]["x.com.samsung.da.desired"] == "180"
 
 
 def test_microwave_setpoint_rmw_preserves_other_item_fields():
-    desc = microwave.MICROWAVE_SETPOINT.entities[0]
+    desc = _microwave_setpoint_desc()
     rep = {
         "x.com.samsung.da.items": [
             {
@@ -94,28 +102,36 @@ def test_microwave_setpoint_rmw_preserves_other_item_fields():
             }
         ]
     }
-    _path, body = desc.write_fn(180, rep)
+    assert desc.write_fn is not None
+    result = desc.write_fn(180, rep)
+    assert result is not None
+    _path, body = result
     item = body["x.com.samsung.da.items"][0]
     assert item["x.com.samsung.da.desired"] == "180"
     assert item["x.com.samsung.da.current"] == "150"
 
 
 def test_microwave_setpoint_clamps_to_step():
-    desc = microwave.MICROWAVE_SETPOINT.entities[0]
+    desc = _microwave_setpoint_desc()
     rep = {"x.com.samsung.da.items": [{"x.com.samsung.da.desired": "0"}]}
-    _, body = desc.write_fn(182, rep)  # nearest 5 = 180
+    assert desc.write_fn is not None
+    result = desc.write_fn(182, rep)  # nearest 5 = 180
+    assert result is not None
+    _, body = result
     assert body["x.com.samsung.da.items"][0]["x.com.samsung.da.desired"] == "180"
 
 
 def test_microwave_setpoint_rejects_out_of_range():
-    desc = microwave.MICROWAVE_SETPOINT.entities[0]
+    desc = _microwave_setpoint_desc()
     rep = {"x.com.samsung.da.items": [{"x.com.samsung.da.desired": "100"}]}
+    assert desc.write_fn is not None
     assert desc.write_fn(20, rep) is None  # below min (40)
     assert desc.write_fn(210, rep) is None  # above max (200)
 
 
 def test_microwave_setpoint_rejects_missing_items():
-    desc = microwave.MICROWAVE_SETPOINT.entities[0]
+    desc = _microwave_setpoint_desc()
+    assert desc.write_fn is not None
     assert desc.write_fn(180, {}) is None
 
 
@@ -123,9 +139,10 @@ def test_microwave_setpoint_exists_only_for_celsius():
     """No Fahrenheit dump exists for this family (unlike oven.py's, verified
     against issue #44) -- the writable setpoint stays hidden rather than
     showing unverified bounds under the wrong unit."""
-    desc = microwave.MICROWAVE_SETPOINT.entities[0]
+    desc = _microwave_setpoint_desc()
     celsius_rep = {"x.com.samsung.da.items": [{"x.com.samsung.da.unit": "Celsius"}]}
     fahrenheit_rep = {"x.com.samsung.da.items": [{"x.com.samsung.da.unit": "Fahrenheit"}]}
+    assert desc.exists_fn is not None
     assert desc.exists_fn(celsius_rep, {}) is True
     assert desc.exists_fn(fahrenheit_rep, {}) is False
 
@@ -157,8 +174,12 @@ def test_power_level_handles_missing_value():
 # ---------------------------------------------------------------------------
 
 
+def _microwave_cooking_mode_desc():
+    return next(e for e in microwave.MICROWAVE_MODE.entities if isinstance(e, SelectDesc))
+
+
 def test_microwave_mode_options_nonempty():
-    desc = microwave.MICROWAVE_MODE.entities[0]
+    desc = _microwave_cooking_mode_desc()
     assert callable(desc.options)
     options = desc.options({})
     assert len(options) > 0
@@ -171,7 +192,7 @@ def test_microwave_mode_options_reads_live_supported_modes():
     _MICROWAVE_MODES -- the live supportedModes list is used verbatim when
     present, same live-first pattern as oven._oven_mode_options, instead of
     offering users modes their own unit doesn't have."""
-    desc = microwave.MICROWAVE_MODE.entities[0]
+    desc = _microwave_cooking_mode_desc()
     resources = {
         "/mode/vs/0": {
             "x.com.samsung.da.supportedModes": ["NoOperation", "MicroWave", "Autocook", "KeepWarm"],
@@ -181,14 +202,18 @@ def test_microwave_mode_options_reads_live_supported_modes():
 
 
 def test_microwave_mode_write_round_trips():
-    desc = microwave.MICROWAVE_MODE.entities[0]
-    path, body = desc.write_fn("MicroWave", {})
+    desc = _microwave_cooking_mode_desc()
+    assert desc.write_fn is not None
+    result = desc.write_fn("MicroWave", {})
+    assert result is not None
+    path, body = result
     assert path == ["mode", "vs", "0"]
     assert body["x.com.samsung.da.modes"] == ["MicroWave"]
 
 
 def test_microwave_mode_rejects_unknown():
-    desc = microwave.MICROWAVE_MODE.entities[0]
+    desc = _microwave_cooking_mode_desc()
+    assert desc.write_fn is not None
     assert desc.write_fn("SpaghettiMode", {}) is None
 
 
@@ -197,9 +222,12 @@ def test_microwave_mode_write_validates_against_live_supported_modes():
     list, not the static union-of-all-dumps fallback -- 'AirFryer' is a
     valid _MICROWAVE_MODES entry but must still be rejected for a unit
     whose own supportedModes doesn't include it."""
-    desc = microwave.MICROWAVE_MODE.entities[0]
+    desc = _microwave_cooking_mode_desc()
     rep = {"x.com.samsung.da.supportedModes": ["NoOperation", "MicroWave", "Autocook", "KeepWarm"]}
-    path, body = desc.write_fn("MicroWave", rep)
+    assert desc.write_fn is not None
+    result = desc.write_fn("MicroWave", rep)
+    assert result is not None
+    path, body = result
     assert path == ["mode", "vs", "0"]
     assert body["x.com.samsung.da.modes"] == ["MicroWave"]
     assert desc.write_fn("AirFryer", rep) is None
@@ -211,9 +239,16 @@ def test_microwave_mode_write_validates_against_live_supported_modes():
 
 
 def test_sound_write_is_single_token():
-    desc = next(e for e in microwave.MICROWAVE_MODE.entities if e.key == "sound")
+    desc = next(
+        e
+        for e in microwave.MICROWAVE_MODE.entities
+        if e.key == "sound" and isinstance(e, SwitchDesc)
+    )
     rep = {"x.com.samsung.da.options": ["Sound_On"]}
-    path, body = desc.write_fn("Off", rep)
+    assert desc.write_fn is not None
+    result = desc.write_fn("Off", rep)
+    assert result is not None
+    path, body = result
     assert path == ["mode", "vs", "0"]
     assert body == {"x.com.samsung.da.options": ["Sound_Off"]}
 
@@ -221,30 +256,52 @@ def test_sound_write_is_single_token():
 def test_lamp_gated_absent_when_no_lamp_option():
     """Issue #121's combi dump has no 'Lamp_*' token at all -- unlike
     oven.py's lamp switch (assumed universal), this one self-gates off."""
-    desc = next(e for e in microwave.MICROWAVE_MODE.entities if e.key == "lamp")
+    desc = next(
+        e
+        for e in microwave.MICROWAVE_MODE.entities
+        if e.key == "lamp" and isinstance(e, SwitchDesc)
+    )
     rep = {"x.com.samsung.da.options": ["DeviceType_MW7300B-/EU1", "Sound_Off"]}
+    assert desc.exists_fn is not None
     assert desc.exists_fn(rep, {}) is False
 
 
 def test_lamp_gated_present_when_lamp_option_reported():
     """Issue #137's plain microwave reports 'Lamp_Off'."""
-    desc = next(e for e in microwave.MICROWAVE_MODE.entities if e.key == "lamp")
+    desc = next(
+        e
+        for e in microwave.MICROWAVE_MODE.entities
+        if e.key == "lamp" and isinstance(e, SwitchDesc)
+    )
     rep = {"x.com.samsung.da.options": ["Lamp_Off", "Sound_On"]}
+    assert desc.exists_fn is not None
     assert desc.exists_fn(rep, {}) is True
 
 
 def test_lamp_write_is_single_token():
     """issue #152: the device has never been observed accepting 'On' --
     only 'High'/'Off' -- so the switch's "on" write uses 'High'."""
-    desc = next(e for e in microwave.MICROWAVE_MODE.entities if e.key == "lamp")
+    desc = next(
+        e
+        for e in microwave.MICROWAVE_MODE.entities
+        if e.key == "lamp" and isinstance(e, SwitchDesc)
+    )
     rep = {"x.com.samsung.da.options": ["Lamp_Off"]}
-    path, body = desc.write_fn("On", rep)
+    assert desc.write_fn is not None
+    result = desc.write_fn("On", rep)
+    assert result is not None
+    path, body = result
     assert path == ["mode", "vs", "0"]
     assert body == {"x.com.samsung.da.options": ["Lamp_High"]}
 
 
 def test_lamp_write_requires_existing_options():
-    desc = next(e for e in microwave.MICROWAVE_MODE.entities if e.key == "lamp")
+    desc = next(
+        e
+        for e in microwave.MICROWAVE_MODE.entities
+        if e.key == "lamp" and isinstance(e, SwitchDesc)
+    )
+    assert desc.write_fn is not None
     assert desc.write_fn("On", {}) is None
 
 
@@ -267,14 +324,24 @@ def test_lamp_reads_any_non_off_level_as_true():
 
 
 def test_filter_remind_gated_absent_when_no_option():
-    desc = next(e for e in microwave.MICROWAVE_MODE.entities if e.key == "filter_remind")
+    desc = next(
+        e
+        for e in microwave.MICROWAVE_MODE.entities
+        if e.key == "filter_remind" and isinstance(e, SwitchDesc)
+    )
     rep = {"x.com.samsung.da.options": ["DeviceType_MW7300B-/EU1", "Sound_Off"]}
+    assert desc.exists_fn is not None
     assert desc.exists_fn(rep, {}) is False
 
 
 def test_filter_remind_gated_present_when_option_reported():
-    desc = next(e for e in microwave.MICROWAVE_MODE.entities if e.key == "filter_remind")
+    desc = next(
+        e
+        for e in microwave.MICROWAVE_MODE.entities
+        if e.key == "filter_remind" and isinstance(e, SwitchDesc)
+    )
     rep = {"x.com.samsung.da.options": ["FilterRemind_Off"]}
+    assert desc.exists_fn is not None
     assert desc.exists_fn(rep, {}) is True
 
 
@@ -285,27 +352,49 @@ def test_filter_remind_reads_on_off():
 
 
 def test_filter_remind_write_is_single_token():
-    desc = next(e for e in microwave.MICROWAVE_MODE.entities if e.key == "filter_remind")
+    desc = next(
+        e
+        for e in microwave.MICROWAVE_MODE.entities
+        if e.key == "filter_remind" and isinstance(e, SwitchDesc)
+    )
     rep = {"x.com.samsung.da.options": ["FilterRemind_Off"]}
-    path, body = desc.write_fn("On", rep)
+    assert desc.write_fn is not None
+    result = desc.write_fn("On", rep)
+    assert result is not None
+    path, body = result
     assert path == ["mode", "vs", "0"]
     assert body == {"x.com.samsung.da.options": ["FilterRemind_On"]}
 
 
 def test_filter_remind_write_requires_existing_options():
-    desc = next(e for e in microwave.MICROWAVE_MODE.entities if e.key == "filter_remind")
+    desc = next(
+        e
+        for e in microwave.MICROWAVE_MODE.entities
+        if e.key == "filter_remind" and isinstance(e, SwitchDesc)
+    )
+    assert desc.write_fn is not None
     assert desc.write_fn("On", {}) is None
 
 
 def test_remind_beep_gated_absent_when_no_option():
-    desc = next(e for e in microwave.MICROWAVE_MODE.entities if e.key == "remind_beep")
+    desc = next(
+        e
+        for e in microwave.MICROWAVE_MODE.entities
+        if e.key == "remind_beep" and isinstance(e, SwitchDesc)
+    )
     rep = {"x.com.samsung.da.options": ["DeviceType_MW7300B-/EU1", "Sound_Off"]}
+    assert desc.exists_fn is not None
     assert desc.exists_fn(rep, {}) is False
 
 
 def test_remind_beep_gated_present_when_option_reported():
-    desc = next(e for e in microwave.MICROWAVE_MODE.entities if e.key == "remind_beep")
+    desc = next(
+        e
+        for e in microwave.MICROWAVE_MODE.entities
+        if e.key == "remind_beep" and isinstance(e, SwitchDesc)
+    )
     rep = {"x.com.samsung.da.options": ["RemindBeep_On"]}
+    assert desc.exists_fn is not None
     assert desc.exists_fn(rep, {}) is True
 
 
@@ -316,13 +405,25 @@ def test_remind_beep_reads_on_off():
 
 
 def test_remind_beep_write_is_single_token():
-    desc = next(e for e in microwave.MICROWAVE_MODE.entities if e.key == "remind_beep")
+    desc = next(
+        e
+        for e in microwave.MICROWAVE_MODE.entities
+        if e.key == "remind_beep" and isinstance(e, SwitchDesc)
+    )
     rep = {"x.com.samsung.da.options": ["RemindBeep_On"]}
-    path, body = desc.write_fn("Off", rep)
+    assert desc.write_fn is not None
+    result = desc.write_fn("Off", rep)
+    assert result is not None
+    path, body = result
     assert path == ["mode", "vs", "0"]
     assert body == {"x.com.samsung.da.options": ["RemindBeep_Off"]}
 
 
 def test_remind_beep_write_requires_existing_options():
-    desc = next(e for e in microwave.MICROWAVE_MODE.entities if e.key == "remind_beep")
+    desc = next(
+        e
+        for e in microwave.MICROWAVE_MODE.entities
+        if e.key == "remind_beep" and isinstance(e, SwitchDesc)
+    )
+    assert desc.write_fn is not None
     assert desc.write_fn("On", {}) is None
diff --git a/tests/test_oven_capabilities.py b/tests/test_oven_capabilities.py
index 800977e..f0981ee 100644
--- a/tests/test_oven_capabilities.py
+++ b/tests/test_oven_capabilities.py
@@ -3,6 +3,11 @@
 from custom_components.localthings.registry.by_type import for_device_by_model
 from custom_components.localthings.registry.capabilities import oven
 from custom_components.localthings.registry.discovery import discover
+from custom_components.localthings.registry.entities import (
+    NumberDesc,
+    SelectDesc,
+    SwitchDesc,
+)
 
 # ---------------------------------------------------------------------------
 # Device-type detection + full-dump coverage (issue #55)
@@ -33,15 +38,21 @@ def test_oven_fixture_resolves_and_has_no_unbound_hrefs():
 # ---------------------------------------------------------------------------
 
 
+def _oven_setpoint_desc():
+    return next(e for e in oven.OVEN_SETPOINT.entities if isinstance(e, NumberDesc))
+
+
 def test_oven_setpoint_write_is_read_modify_write():
-    cap = oven.OVEN_SETPOINT
-    desc = cap.entities[0]
+    desc = _oven_setpoint_desc()
     rep = {
         "x.com.samsung.da.items": [
             {"x.com.samsung.da.id": "Target", "x.com.samsung.da.temperature": 0}
         ]
     }
-    path, body = desc.write_fn(200, rep)
+    assert desc.write_fn is not None
+    result = desc.write_fn(200, rep)
+    assert result is not None
+    path, body = result
     assert path[-1] == "0"  # writes back to the resource
     # the produced body preserves the items-array shape the oven expects
     assert "x.com.samsung.da.items" in body or "x.com.samsung.da.temperature" in str(body)
@@ -49,7 +60,7 @@ def test_oven_setpoint_write_is_read_modify_write():
 
 def test_oven_setpoint_rmw_preserves_other_item_fields():
     """RMW must not drop sibling fields (e.g. x.com.samsung.da.current)."""
-    desc = oven.OVEN_SETPOINT.entities[0]
+    desc = _oven_setpoint_desc()
     rep = {
         "x.com.samsung.da.items": [
             {
@@ -58,7 +69,10 @@ def test_oven_setpoint_rmw_preserves_other_item_fields():
             }
         ]
     }
-    _path, body = desc.write_fn(200, rep)
+    assert desc.write_fn is not None
+    result = desc.write_fn(200, rep)
+    assert result is not None
+    _path, body = result
     item = body["x.com.samsung.da.items"][0]
     assert item["x.com.samsung.da.desired"] == "200"
     # sibling field preserved
@@ -67,22 +81,27 @@ def test_oven_setpoint_rmw_preserves_other_item_fields():
 
 def test_oven_setpoint_clamps_to_step():
     """Setpoint must be a multiple of SETPOINT_STEP_C."""
-    desc = oven.OVEN_SETPOINT.entities[0]
+    desc = _oven_setpoint_desc()
     rep = {"x.com.samsung.da.items": [{"x.com.samsung.da.desired": "0"}]}
-    _, body = desc.write_fn(202, rep)
+    assert desc.write_fn is not None
+    result = desc.write_fn(202, rep)
+    assert result is not None
+    _, body = result
     # 202 → nearest 5 = 200
     assert body["x.com.samsung.da.items"][0]["x.com.samsung.da.desired"] == "200"
 
 
 def test_oven_setpoint_rejects_out_of_range():
-    desc = oven.OVEN_SETPOINT.entities[0]
+    desc = _oven_setpoint_desc()
     rep = {"x.com.samsung.da.items": [{"x.com.samsung.da.desired": "100"}]}
+    assert desc.write_fn is not None
     assert desc.write_fn(10, rep) is None  # below min (30)
     assert desc.write_fn(300, rep) is None  # above max (270)
 
 
 def test_oven_setpoint_rejects_missing_items():
-    desc = oven.OVEN_SETPOINT.entities[0]
+    desc = _oven_setpoint_desc()
+    assert desc.write_fn is not None
     assert desc.write_fn(200, {}) is None
 
 
@@ -105,24 +124,31 @@ def _fahrenheit_rep(desired="0"):
 
 
 def test_oven_setpoint_write_uses_fahrenheit_bounds():
-    desc = oven.OVEN_SETPOINT.entities[0]
+    desc = _oven_setpoint_desc()
     rep = _fahrenheit_rep()
     # 350 is within F bounds (175-550) but above the C max (270) --
     # confirms the write path isn't silently still clamping to Celsius.
-    _, body = desc.write_fn(350, rep)
+    assert desc.write_fn is not None
+    result = desc.write_fn(350, rep)
+    assert result is not None
+    _, body = result
     assert body["x.com.samsung.da.items"][0]["x.com.samsung.da.desired"] == "350"
 
 
 def test_oven_setpoint_rejects_out_of_range_fahrenheit():
-    desc = oven.OVEN_SETPOINT.entities[0]
+    desc = _oven_setpoint_desc()
     rep = _fahrenheit_rep()
+    assert desc.write_fn is not None
     assert desc.write_fn(100, rep) is None  # below F min (175)
     assert desc.write_fn(600, rep) is None  # above F max (550)
 
 
 def test_oven_setpoint_native_bounds_track_live_unit():
-    desc = oven.OVEN_SETPOINT.entities[0]
+    desc = _oven_setpoint_desc()
     celsius_rep = {"x.com.samsung.da.items": [{"x.com.samsung.da.unit": "Celsius"}]}
+    assert desc.native_min_fn is not None
+    assert desc.native_max_fn is not None
+    assert desc.step_fn is not None
     assert desc.native_min_fn(celsius_rep) == 30.0
     assert desc.native_max_fn(celsius_rep) == 270.0
     fahrenheit_rep = _fahrenheit_rep()
@@ -136,21 +162,25 @@ def test_oven_setpoint_native_bounds_track_live_unit():
 # ---------------------------------------------------------------------------
 
 
+def _oven_mode_desc():
+    return next(e for e in oven.OVEN_MODE.entities if isinstance(e, SelectDesc))
+
+
 def test_oven_mode_options_nonempty():
-    desc = oven.OVEN_MODE.entities[0]
+    desc = _oven_mode_desc()
     assert callable(desc.options)
     assert len(desc.options({})) > 0
 
 
 def test_oven_mode_options_falls_back_when_no_live_supported_modes():
-    desc = oven.OVEN_MODE.entities[0]
+    desc = _oven_mode_desc()
     assert desc.options({}) == list(oven._OVEN_MODES)
 
 
 def test_oven_mode_options_reads_live_supported_modes():
     """issue #138: the device's own supportedModes list is used verbatim
     when present, instead of the static _OVEN_MODES guess."""
-    desc = oven.OVEN_MODE.entities[0]
+    desc = _oven_mode_desc()
     resources = {
         "/mode/vs/0": {
             "x.com.samsung.da.supportedModes": ["Bake", "AirFryer", "SelfClean"],
@@ -160,15 +190,19 @@ def test_oven_mode_options_reads_live_supported_modes():
 
 
 def test_oven_mode_write_round_trips():
-    desc = oven.OVEN_MODE.entities[0]
+    desc = _oven_mode_desc()
     valid_mode = desc.options({})[1]  # e.g. 'Bake'
-    path, body = desc.write_fn(valid_mode, {})
+    assert desc.write_fn is not None
+    result = desc.write_fn(valid_mode, {})
+    assert result is not None
+    path, body = result
     assert path == ["mode", "vs", "0"]
     assert body["x.com.samsung.da.modes"] == [valid_mode]
 
 
 def test_oven_mode_rejects_unknown():
-    desc = oven.OVEN_MODE.entities[0]
+    desc = _oven_mode_desc()
+    assert desc.write_fn is not None
     assert desc.write_fn("SpaghettiMode", {}) is None
 
 
@@ -177,9 +211,12 @@ def test_oven_mode_write_validates_against_live_supported_modes():
     list, not the static fallback -- issue #138's AirFryer/SelfClean/etc.
     are accepted, and a mode outside the device's own list is rejected even
     if some other model's static guess would have allowed it."""
-    desc = oven.OVEN_MODE.entities[0]
+    desc = _oven_mode_desc()
     rep = {"x.com.samsung.da.supportedModes": ["Bake", "AirFryer", "SelfClean"]}
-    path, body = desc.write_fn("AirFryer", rep)
+    assert desc.write_fn is not None
+    result = desc.write_fn("AirFryer", rep)
+    assert result is not None
+    path, body = result
     assert path == ["mode", "vs", "0"]
     assert body["x.com.samsung.da.modes"] == ["AirFryer"]
     assert desc.write_fn("FrozenPizzaPlus", rep) is None
@@ -205,20 +242,29 @@ def _mode_rep(*extra_opts):
 
 
 def test_lamp_write_is_single_token():
-    desc = next(e for e in oven.OVEN_MODE.entities if e.key == "lamp")
-    path, body = desc.write_fn("On", _mode_rep())
+    desc = next(e for e in oven.OVEN_MODE.entities if e.key == "lamp" and isinstance(e, SwitchDesc))
+    assert desc.write_fn is not None
+    result = desc.write_fn("On", _mode_rep())
+    assert result is not None
+    path, body = result
     assert path == ["mode", "vs", "0"]
     assert body == {"x.com.samsung.da.options": ["UpperLamp_On"]}
 
 
 def test_lamp_write_requires_existing_options():
-    desc = next(e for e in oven.OVEN_MODE.entities if e.key == "lamp")
+    desc = next(e for e in oven.OVEN_MODE.entities if e.key == "lamp" and isinstance(e, SwitchDesc))
+    assert desc.write_fn is not None
     assert desc.write_fn("On", {}) is None
 
 
 def test_sound_write_is_single_token():
-    desc = next(e for e in oven.OVEN_MODE.entities if e.key == "sound")
-    _path, body = desc.write_fn("Off", _mode_rep())
+    desc = next(
+        e for e in oven.OVEN_MODE.entities if e.key == "sound" and isinstance(e, SwitchDesc)
+    )
+    assert desc.write_fn is not None
+    result = desc.write_fn("Off", _mode_rep())
+    assert result is not None
+    _path, body = result
     assert body == {"x.com.samsung.da.options": ["Sound_Off"]}
 
 
@@ -226,8 +272,13 @@ def test_natural_steam_write_is_single_token():
     """NaturalSteam's slot may be absent from the live rep until first
     write -- the single-token write covers both the insert and replace case
     identically, since the device merges by prefix either way."""
-    desc = next(e for e in oven.OVEN_MODE.entities if e.key == "natural_steam")
-    _path, body = desc.write_fn("On", _mode_rep())  # no NaturalSteam_* in rep
+    desc = next(
+        e for e in oven.OVEN_MODE.entities if e.key == "natural_steam" and isinstance(e, SwitchDesc)
+    )
+    assert desc.write_fn is not None
+    result = desc.write_fn("On", _mode_rep())  # no NaturalSteam_* in rep
+    assert result is not None
+    _path, body = result
     assert body == {"x.com.samsung.da.options": ["NaturalSteam_On"]}
 
 
@@ -254,14 +305,26 @@ def test_cycle_active_false_when_idle():
 
 
 def test_cook_time_write_produces_hms():
-    desc = next(e for e in oven.OVEN_OPERATIONAL_STATE.entities if e.key == "cook_time")
-    path, body = desc.write_fn(90, {})
+    desc = next(
+        e
+        for e in oven.OVEN_OPERATIONAL_STATE.entities
+        if e.key == "cook_time" and isinstance(e, NumberDesc)
+    )
+    assert desc.write_fn is not None
+    result = desc.write_fn(90, {})
+    assert result is not None
+    path, body = result
     assert path == ["operational", "state", "vs", "0"]
     assert body["x.com.samsung.da.operationTime"] == "01:30:00"
     assert body["x.com.samsung.da.remainingTime"] == "01:30:00"
 
 
 def test_cook_time_rejects_out_of_range():
-    desc = next(e for e in oven.OVEN_OPERATIONAL_STATE.entities if e.key == "cook_time")
+    desc = next(
+        e
+        for e in oven.OVEN_OPERATIONAL_STATE.entities
+        if e.key == "cook_time" and isinstance(e, NumberDesc)
+    )
+    assert desc.write_fn is not None
     assert desc.write_fn(-1, {}) is None
     assert desc.write_fn(1440, {}) is None
diff --git a/tests/test_range_hood_fan.py b/tests/test_range_hood_fan.py
index 9043589..4eafe92 100644
--- a/tests/test_range_hood_fan.py
+++ b/tests/test_range_hood_fan.py
@@ -1,7 +1,8 @@
 """HA fan-entity mapping tests for the range hood."""
 
-from typing import ClassVar
+from typing import ClassVar, cast
 
+from custom_components.localthings.coordinator import LocalThingsCoordinator
 from custom_components.localthings.fan import LocalThingsRangeHoodFan
 from custom_components.localthings.registry.by_type import microwave, range_hood
 from custom_components.localthings.registry.discovery import discover
@@ -39,7 +40,7 @@ def _entity(resources, coordinator=None, registry=range_hood.REGISTRY):
     )
     fan_bound = next(item for item in bound if isinstance(item.desc, FanDesc))
     return LocalThingsRangeHoodFan(
-        coordinator or _FakeCoordinator(resources),
+        cast(LocalThingsCoordinator, coordinator or _FakeCoordinator(resources)),
         fan_bound,
     )
 
diff --git a/tests/test_range_ne63a6511_capabilities.py b/tests/test_range_ne63a6511_capabilities.py
index 436bf4e..fd4a4c4 100644
--- a/tests/test_range_ne63a6511_capabilities.py
+++ b/tests/test_range_ne63a6511_capabilities.py
@@ -5,10 +5,13 @@ hrefs, plus oven.OVEN_MODE reading this dump's ConvectionRoast/KeepWarm/
 BreadProof/AirFryer/Dehydrate/SelfClean/SteamClean modes live from its own
 /mode/vs/0 supportedModes rather than needing them hardcoded."""
 
+from typing import cast
+
 from custom_components.localthings.registry.adapter import flatten
 from custom_components.localthings.registry.by_type import for_device_by_resources
 from custom_components.localthings.registry.capabilities import oven
 from custom_components.localthings.registry.discovery import discover
+from custom_components.localthings.registry.entities import SelectDesc
 from tests.conftest import _load_device
 
 
@@ -64,7 +67,9 @@ def test_oven_mode_accepts_this_devices_supported_modes():
     those modes added to any Python list."""
     _, resources = _range()
     live_rep = resources["/mode/vs/0"]
-    desc = oven.OVEN_MODE.entities[0]
+    desc = cast(SelectDesc, oven.OVEN_MODE.entities[0])
+    assert desc.options is not None
+    assert desc.write_fn is not None
     assert desc.options(resources) == live_rep["x.com.samsung.da.supportedModes"]
     for mode in (
         "ConvectionRoast",
@@ -75,6 +80,8 @@ def test_oven_mode_accepts_this_devices_supported_modes():
         "SelfClean",
         "SteamClean",
     ):
-        path, body = desc.write_fn(mode, live_rep)
+        result = desc.write_fn(mode, live_rep)
+        assert result is not None
+        path, body = result
         assert path == ["mode", "vs", "0"]
         assert body["x.com.samsung.da.modes"] == [mode]
diff --git a/tests/test_unique_ids.py b/tests/test_unique_ids.py
index b4f9d6f..f679508 100644
--- a/tests/test_unique_ids.py
+++ b/tests/test_unique_ids.py
@@ -7,9 +7,11 @@ capable or not -- exercises it automatically.
 """
 
 from collections import Counter
+from typing import cast
 
 import pytest
 
+from custom_components.localthings.coordinator import LocalThingsCoordinator
 from custom_components.localthings.entity import _is_included
 from custom_components.localthings.registry.adapter import _key
 from custom_components.localthings.registry.entities import PLATFORM_OF
@@ -57,7 +59,7 @@ def test_key_is_unique_across_all_bound_entities(name):
         oic_res,
         seeds,
     )
-    coordinator = _FakeCoordinator(full_resources, materialized)
+    coordinator = cast(LocalThingsCoordinator, _FakeCoordinator(full_resources, materialized))
     included = [b for b in bound if _is_included(b, coordinator)]
     keys = [(PLATFORM_OF[type(b.desc)], _key(b)) for b in included]
     dupes = {k: n for k, n in Counter(keys).items() if n > 1}
diff --git a/tests/test_water_heater_ehs.py b/tests/test_water_heater_ehs.py
index d3a6b3c..d3dc935 100644
--- a/tests/test_water_heater_ehs.py
+++ b/tests/test_water_heater_ehs.py
@@ -1,6 +1,6 @@
 """HA water_heater-entity mapping tests for the EHS DHW loop."""
 
-from typing import ClassVar
+from typing import ClassVar, cast
 
 from homeassistant.components.water_heater import (
     STATE_ECO,
@@ -11,6 +11,7 @@ from homeassistant.components.water_heater import (
 )
 from homeassistant.const import STATE_OFF, UnitOfTemperature
 
+from custom_components.localthings.coordinator import LocalThingsCoordinator
 from custom_components.localthings.registry.by_type import ehs
 from custom_components.localthings.registry.discovery import discover
 from custom_components.localthings.registry.entities import WaterHeaterDesc
@@ -47,7 +48,9 @@ def _entity(resources, coordinator=None):
         ehs.REGISTRY.pattern_capabilities,
     )
     water_heater_bound = next(item for item in bound if isinstance(item.desc, WaterHeaterDesc))
-    return LocalThingsWaterHeater(coordinator or _FakeCoordinator(resources), water_heater_bound)
+    return LocalThingsWaterHeater(
+        cast(LocalThingsCoordinator, coordinator or _FakeCoordinator(resources)), water_heater_bound
+    )
 
 
 def test_current_operation_reads_eco_when_on():