diff --git a/tests/localthings/test_config_flow.py b/tests/localthings/test_config_flow.py
index f880b6b..4dd8e2d 100644
--- a/tests/localthings/test_config_flow.py
+++ b/tests/localthings/test_config_flow.py
@@ -2,6 +2,7 @@
 
 from __future__ import annotations
 
+from typing import Iterable, cast
 from unittest.mock import patch
 
 from homeassistant.core import HomeAssistant
@@ -32,8 +33,10 @@ async def test_form_first_device(hass: HomeAssistant) -> None:
     result = await hass.config_entries.flow.async_init(DOMAIN, context={"source": "user"})
     assert result["type"] == FlowResultType.FORM
     assert result["step_id"] == "user"
-    assert CONF_CA_CERT_PEM in result["data_schema"].schema
-    assert CONF_CA_KEY_PEM in result["data_schema"].schema
+    data_schema = result["data_schema"]
+    assert data_schema is not None
+    assert CONF_CA_CERT_PEM in data_schema.schema
+    assert CONF_CA_KEY_PEM in data_schema.schema
 
 
 async def test_form_second_device_reuses_creds(hass: HomeAssistant) -> None:
@@ -44,8 +47,10 @@ async def test_form_second_device_reuses_creds(hass: HomeAssistant) -> None:
     result = await hass.config_entries.flow.async_init(DOMAIN, context={"source": "user"})
     assert result["type"] == FlowResultType.FORM
     assert result["step_id"] == "user_reuse"
-    assert CONF_CA_CERT_PEM not in result["data_schema"].schema
-    assert CONF_CA_KEY_PEM not in result["data_schema"].schema
+    data_schema = result["data_schema"]
+    assert data_schema is not None
+    assert CONF_CA_CERT_PEM not in data_schema.schema
+    assert CONF_CA_KEY_PEM not in data_schema.schema
 
 
 async def test_successful_setup(hass: HomeAssistant, mock_probe) -> None:
@@ -243,7 +248,9 @@ async def test_cannot_connect(hass: HomeAssistant) -> None:
             },
         )
     assert result["type"] == FlowResultType.FORM
-    assert result["errors"]["base"] == "cannot_connect"
+    errors = result["errors"]
+    assert errors is not None
+    assert errors["base"] == "cannot_connect"
 
 
 async def test_recognized_type_skips_confirmation_step(hass: HomeAssistant, mock_probe) -> None:
@@ -368,7 +375,7 @@ async def test_options_flow_init_shows_menu(hass: HomeAssistant) -> None:
 
     assert result["type"] == FlowResultType.MENU
     assert result["step_id"] == "init"
-    assert set(result["menu_options"]) == {"settings", "debug_write"}
+    assert set(cast(Iterable[str], result["menu_options"])) == {"settings", "debug_write"}
 
 
 async def test_options_flow_default_is_off(hass: HomeAssistant) -> None:
@@ -384,7 +391,9 @@ async def test_options_flow_default_is_off(hass: HomeAssistant) -> None:
 
     assert result["type"] == FlowResultType.FORM
     assert result["step_id"] == "settings"
-    assert result["data_schema"]({})[CONF_BYPASS_REMOTE_CONTROL] is False
+    data_schema = result["data_schema"]
+    assert data_schema is not None
+    assert data_schema({})[CONF_BYPASS_REMOTE_CONTROL] is False
 
 
 async def test_options_flow_can_enable_bypass(hass: HomeAssistant) -> None:
@@ -421,7 +430,9 @@ async def test_options_flow_reflects_previously_saved_value(hass: HomeAssistant)
         result["flow_id"], user_input={"next_step_id": "settings"}
     )
 
-    assert result["data_schema"]({})[CONF_BYPASS_REMOTE_CONTROL] is True
+    data_schema = result["data_schema"]
+    assert data_schema is not None
+    assert data_schema({})[CONF_BYPASS_REMOTE_CONTROL] is True
 
 
 async def test_options_flow_debug_write_shows_hrefs_from_coordinator(
@@ -495,7 +506,9 @@ async def test_options_flow_debug_edit_writes_and_shows_result(
 
     assert result["type"] == FlowResultType.MENU
     assert result["step_id"] == "debug_result"
-    assert result["description_placeholders"]["code"] == "2.04 (0x44)"
+    description_placeholders = result["description_placeholders"]
+    assert description_placeholders is not None
+    assert description_placeholders["code"] == "2.04 (0x44)"
 
 
 async def test_options_flow_debug_edit_rejects_empty_payload(
diff --git a/tests/localthings/test_coordinator.py b/tests/localthings/test_coordinator.py
index 5eb6b8e..36deccd 100644
--- a/tests/localthings/test_coordinator.py
+++ b/tests/localthings/test_coordinator.py
@@ -291,7 +291,9 @@ def test_logger_is_scoped_to_device_host(hass: HomeAssistant, mock_entry) -> Non
     makes multi-device logs ambiguous."""
     coordinator = LocalThingsCoordinator(hass, mock_entry)
 
-    assert coordinator._log.name.endswith(ENTRY_DATA[CONF_HOST])
+    host = ENTRY_DATA[CONF_HOST]
+    assert isinstance(host, str)
+    assert coordinator._log.name.endswith(host)
     assert coordinator.logger is coordinator._log
     assert coordinator._observe.log is coordinator._log
 
@@ -393,7 +395,9 @@ async def test_reconnect_while_observe_mode_downgrades_to_poll(
     # still alive (see test_poll_failure_skips_reconnect_when_push_is_healthy)
     # and would not trigger a reconnect at all. This test covers a
     # genuinely dead channel: no recent push, poll fails, reconnect fires.
-    coordinator._observe._last_notify_ts -= PUSH_HEALTH_WINDOW_S + 1
+    last_notify_ts = coordinator._observe._last_notify_ts
+    assert last_notify_ts is not None
+    coordinator._observe._last_notify_ts = last_notify_ts - (PUSH_HEALTH_WINDOW_S + 1)
 
     # Simulate the existing "poll failed, reconnecting" branch: _poll_once
     # fails once (triggering the reconnect/backoff path), then succeeds.
@@ -490,7 +494,9 @@ async def test_poll_timeout_reconnects_after_consecutive_limit_even_with_push(
 
     # No notify is recent any more, so every timeout below counts toward
     # the consecutive-timeout limit instead of being deferred.
-    coordinator._observe._last_notify_ts -= PUSH_HEALTH_WINDOW_S + 1
+    last_notify_ts = coordinator._observe._last_notify_ts
+    assert last_notify_ts is not None
+    coordinator._observe._last_notify_ts = last_notify_ts - (PUSH_HEALTH_WINDOW_S + 1)
 
     # Call _async_update_data directly rather than via
     # async_request_refresh() — the coordinator's built-in debouncer
@@ -553,7 +559,9 @@ async def test_poll_timeout_counter_resets_when_push_is_healthy_again(
     assert coordinator.observe_mode == MODE_OBSERVE
 
     # Age the notify out so timeouts accrue toward the limit.
-    coordinator._observe._last_notify_ts -= PUSH_HEALTH_WINDOW_S + 1
+    last_notify_ts = coordinator._observe._last_notify_ts
+    assert last_notify_ts is not None
+    coordinator._observe._last_notify_ts = last_notify_ts - (PUSH_HEALTH_WINDOW_S + 1)
     with patch(
         "custom_components.localthings.coordinator.LocalThingsCoordinator._poll_once",
         side_effect=TimeoutError("GET /device/0 block 11 timeout"),
@@ -605,7 +613,9 @@ async def test_reconnect_from_observe_mode_resubscribes_immediately(
     # failure below actually triggers a reconnect (see
     # test_poll_failure_skips_reconnect_when_push_is_healthy for the
     # healthy-push case, which now skips reconnecting entirely).
-    coordinator._observe._last_notify_ts -= PUSH_HEALTH_WINDOW_S + 1
+    last_notify_ts = coordinator._observe._last_notify_ts
+    assert last_notify_ts is not None
+    coordinator._observe._last_notify_ts = last_notify_ts - (PUSH_HEALTH_WINDOW_S + 1)
 
     # If a stale retry timer (rather than an immediate resubscribe) were
     # driving recovery, mode would still be 'poll' right after this single
@@ -734,7 +744,7 @@ async def test_write_marks_href_pending_before_post(
     await hass.async_block_till_done()
     coordinator: LocalThingsCoordinator = hass.data[DOMAIN][mock_entry.entry_id]
 
-    def _write_fn(payload, rep, href):
+    def _write_fn(payload, rep, href=None):
         return (["some", "path"], {"value": payload})
 
     desc = NumberDesc(key="test", field="value", write_fn=_write_fn)
@@ -771,7 +781,7 @@ async def test_send_command_applies_write_optimistically_before_settling(
     await hass.async_block_till_done()
     coordinator: LocalThingsCoordinator = hass.data[DOMAIN][mock_entry.entry_id]
 
-    def _write_fn(payload, rep, href):
+    def _write_fn(payload, rep, href=None):
         return (["some", "path"], {"value": payload})
 
     desc = NumberDesc(key="test", field="value", write_fn=_write_fn)
@@ -812,8 +822,10 @@ async def test_climate_power_write_applies_to_its_own_href_not_bound_href(
     await hass.async_block_till_done()
     coordinator: LocalThingsCoordinator = hass.data[DOMAIN][mock_entry.entry_id]
 
+    climate_href = airconditioner.CLIMATE.href
+    assert climate_href is not None
     bound = BoundEntity(
-        href=airconditioner.CLIMATE.href,
+        href=climate_href,
         capability=coordinator.bound[0].capability,
         desc=airconditioner.CLIMATE.entities[0],
     )
@@ -823,9 +835,7 @@ async def test_climate_power_write_applies_to_its_own_href_not_bound_href(
         await coordinator.async_send_command(bound, ("power", True))
 
     assert (coordinator._cache.get("/power/vs/0") or {}).get("x.com.samsung.da.power") == "On"
-    assert "x.com.samsung.da.power" not in (
-        coordinator._cache.get(airconditioner.CLIMATE.href) or {}
-    )
+    assert "x.com.samsung.da.power" not in (coordinator._cache.get(climate_href) or {})
     assert coordinator._observe._settle_until.get("/power/vs/0") is not None
 
 
@@ -858,7 +868,7 @@ async def test_send_command_survives_stale_confirm_poll(
     await hass.async_block_till_done()
     coordinator: LocalThingsCoordinator = hass.data[DOMAIN][mock_entry.entry_id]
 
-    def _write_fn(payload, rep, href):
+    def _write_fn(payload, rep, href=None):
         return (["test", "vs", "0"], {"value": payload})
 
     desc = NumberDesc(key="test", field="value", write_fn=_write_fn)
@@ -917,12 +927,12 @@ async def test_second_write_to_same_href_lands_during_first_writes_settle_window
     desc_a = NumberDesc(
         key="cycle",
         field="cycle",
-        write_fn=lambda p, rep, href: (["test", "vs", "0"], {"cycle": p}),
+        write_fn=lambda p, rep, href=None: (["test", "vs", "0"], {"cycle": p}),
     )
     desc_b = NumberDesc(
         key="detergent",
         field="detergent",
-        write_fn=lambda p, rep, href: (["test", "vs", "0"], {"detergent": p}),
+        write_fn=lambda p, rep, href=None: (["test", "vs", "0"], {"detergent": p}),
     )
     bound_a = BoundEntity(
         href="/test/vs/0", capability=coordinator.bound[0].capability, desc=desc_a
@@ -1023,7 +1033,7 @@ async def test_send_command_blocked_when_remote_control_disabled(
         source="test",
     )
 
-    def _write_fn(payload, rep, href):
+    def _write_fn(payload, rep, href=None):
         return (["some", "path"], {"value": payload})
 
     desc = NumberDesc(key="test", field="value", write_fn=_write_fn)
@@ -1064,7 +1074,7 @@ async def test_send_command_allowed_when_remote_control_enabled(
         source="test",
     )
 
-    def _write_fn(payload, rep, href):
+    def _write_fn(payload, rep, href=None):
         return (["some", "path"], {"value": payload})
 
     desc = NumberDesc(key="test", field="value", write_fn=_write_fn)
@@ -1139,7 +1149,7 @@ async def test_send_command_bypasses_remote_control_when_option_enabled(
         source="test",
     )
 
-    def _write_fn(payload, rep, href):
+    def _write_fn(payload, rep, href=None):
         return (["some", "path"], {"value": payload})
 
     desc = NumberDesc(key="test", field="value", write_fn=_write_fn)
diff --git a/tests/localthings/test_observe.py b/tests/localthings/test_observe.py
index 33bc7bf..5a24766 100644
--- a/tests/localthings/test_observe.py
+++ b/tests/localthings/test_observe.py
@@ -53,6 +53,7 @@ def test_apply_merges_partial_update_onto_prior_rep():
     mgr.apply("/mode/vs/0", partial, source="observe")
 
     cached = mgr.cache.get("/mode/vs/0")
+    assert cached is not None
     assert cached["x.com.samsung.da.modes"] == ["CVN_CONVERTIBLE_ZONE", "WATERFILTER_ENABLE"]
     assert cached["x.com.samsung.da.supportedOptions"] == ["CV_FDR_WINE", "CV_FDR_MEAT"]
 
@@ -435,6 +436,7 @@ def test_close_stops_the_refresh_thread():
     session = _FakeSession()
     mgr.start_refresh_task(session)
     thread = mgr._refresh_thread
+    assert thread is not None
 
     mgr.close()
     thread.join(timeout=2.0)
@@ -449,6 +451,7 @@ def test_downgrade_to_poll_stops_refresh_task():
     session = _FakeSession()
     mgr.start_refresh_task(session)
     thread = mgr._refresh_thread
+    assert thread is not None
 
     mgr.downgrade_to_poll()
     thread.join(timeout=2.0)
diff --git a/tests/test_air_purifier_capabilities.py b/tests/test_air_purifier_capabilities.py
index aed9871..bfa4816 100644
--- a/tests/test_air_purifier_capabilities.py
+++ b/tests/test_air_purifier_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 air_purifier
 from custom_components.localthings.registry.discovery import discover
+from custom_components.localthings.registry.entities import FanDesc, SensorDesc, SwitchDesc
 from tests.conftest import _load_device
 
 
@@ -90,7 +91,9 @@ def test_light_switch_write_contract():
     (via laundry.option_write) -- confirmed on real hardware (issue #54)
     that the device merges by prefix itself, so no read-modify-write of the
     whole packed /mode/vs/0 options list is needed."""
-    desc = next(e for e in air_purifier.MODE.entities if e.key == "display_light")
+    desc = next(
+        e for e in air_purifier.MODE.entities if e.key == "display_light" and isinstance(e, SwitchDesc)
+    )
     rep = {
         "x.com.samsung.da.options": [
             "Comode_Off",
@@ -99,7 +102,9 @@ def test_light_switch_write_contract():
             "OptionCode_60282",
         ]
     }
+    assert desc.rep_fn is not None
     assert desc.rep_fn(rep) is True
+    assert desc.write_fn is not None
     assert desc.write_fn("Off", rep) == (
         ["mode", "vs", "0"],
         {"x.com.samsung.da.options": ["Light_Off"]},
@@ -112,8 +117,11 @@ def test_operating_mode_is_a_read_only_diagnostic():
     regardless of the device's actual fan setting, ruling out the original
     guess that it was the fan-speed selector; its real purpose is still
     unconfirmed (see the air_purifier.py module docstring)."""
-    operating_mode = next(e for e in air_purifier.MODE.entities if e.key == "operating_mode")
+    operating_mode = next(
+        e for e in air_purifier.MODE.entities if e.key == "operating_mode" and isinstance(e, SensorDesc)
+    )
     rep = {"x.com.samsung.da.options": ["Comode_Off"]}
+    assert operating_mode.rep_fn is not None
     assert operating_mode.rep_fn(rep) == "Off"
     assert not hasattr(operating_mode, "write_fn")
 
@@ -128,14 +136,16 @@ def test_blooming_not_modeled():
 def test_airflow_vs_fallback_only_binds_without_generic():
     """/airflow/vs/0 is a match_fn fallback -- it must not bind when the
     OCF-standard /airflow/0 is also present (both are on every dump seen)."""
+    match_fn = air_purifier.AIRFLOW_VS_FALLBACK.match_fn
+    assert match_fn is not None
     assert (
-        air_purifier.AIRFLOW_VS_FALLBACK.match_fn(
+        match_fn(
             {},
             {"/airflow/0": {"speed": 0, "direction": "Off"}},
         )
         is False
     )
-    assert air_purifier.AIRFLOW_VS_FALLBACK.match_fn({}, {}) is True
+    assert match_fn({}, {}) is True
 
 
 def test_airflow_fan_write_contract():
@@ -143,7 +153,10 @@ def test_airflow_fan_write_contract():
     (two independent units, 60-90s apart per setting): /airflow/0's `speed`
     is a clean, monotonic 0-4 code, so the write is a plain int passthrough
     -- no named-preset table needed (see fan.py's LocalThingsAirflowFan)."""
-    fan_desc = next(e for e in air_purifier.AIRFLOW_GENERIC.entities if e.key == "airflow_fan")
+    fan_desc = next(
+        e for e in air_purifier.AIRFLOW_GENERIC.entities if e.key == "airflow_fan" and isinstance(e, FanDesc)
+    )
+    assert fan_desc.write_fn is not None
     assert fan_desc.write_fn(("speed", 3), {}) == (["airflow", "0"], {"speed": 3})
     assert fan_desc.write_fn(("power", True, "/power/vs/0"), {}) == (
         ["power", "vs", "0"],
diff --git a/tests/test_dishwasher_capabilities.py b/tests/test_dishwasher_capabilities.py
index 5cfb7b6..1e9d232 100644
--- a/tests/test_dishwasher_capabilities.py
+++ b/tests/test_dishwasher_capabilities.py
@@ -6,6 +6,7 @@ check the dishwasher wiring and its device-specific options.
 """
 
 from custom_components.localthings.registry.capabilities import dishwasher, laundry
+from custom_components.localthings.registry.entities import SwitchDesc
 
 
 class TestCycleOptions:
@@ -34,14 +35,27 @@ class TestCycleOptions:
 
 class TestDishwasherOptions:
     def test_storm_wash_read_and_write(self):
-        desc = next(e for e in dishwasher.CYCLE_OPTIONS.entities if e.key == "storm_wash")
+        desc = next(
+            e
+            for e in dishwasher.CYCLE_OPTIONS.entities
+            if e.key == "storm_wash" and isinstance(e, SwitchDesc)
+        )
+        assert desc.rep_fn is not None
         assert desc.rep_fn({"x.com.samsung.da.options": ["StormWashZone_On"]}) is True
         assert desc.rep_fn({"x.com.samsung.da.options": ["StormWashZone_Off"]}) is False
-        path, body = desc.write_fn("Off", {"x.com.samsung.da.options": ["StormWashZone_On"]})
+        assert desc.write_fn is not None
+        result = desc.write_fn("Off", {"x.com.samsung.da.options": ["StormWashZone_On"]})
+        assert result is not None
+        path, body = result
         assert path == ["course", "vs", "0"]
         assert "StormWashZone_Off" in body["x.com.samsung.da.options"]
 
     def test_auto_release_exists_only_when_field_present(self):
-        desc = next(e for e in dishwasher.CYCLE_OPTIONS.entities if e.key == "auto_release_dry")
+        desc = next(
+            e
+            for e in dishwasher.CYCLE_OPTIONS.entities
+            if e.key == "auto_release_dry" and isinstance(e, SwitchDesc)
+        )
+        assert desc.exists_fn is not None
         assert desc.exists_fn({"x.com.samsung.da.options": []}, {}) is False
         assert desc.exists_fn({"x.com.samsung.da.options": ["AutoDoorRelease_On"]}, {}) is True
diff --git a/tests/test_entities.py b/tests/test_entities.py
index c897015..b0cd81c 100644
--- a/tests/test_entities.py
+++ b/tests/test_entities.py
@@ -20,7 +20,13 @@ def test_value_fn_defaults_to_identity():
 def test_descriptions_are_frozen():
     d = SensorDesc(key="power", field="f")
     try:
-        d.key = "other"
+        # setattr() through a variable name (not `d.key = "other"`, and not a
+        # literal setattr(d, "key", ...) -- ruff's B010 rewrites that back to
+        # attribute-assignment syntax), so this reaches the same
+        # frozen-dataclass __setattr__ at runtime without ty statically
+        # flagging the (deliberately illegal) direct attribute assignment.
+        attr = "key"
+        setattr(d, attr, "other")
     except Exception as e:
         assert "frozen" in str(type(e)).lower() or "cannot" in str(e).lower()
     else:
@@ -46,4 +52,5 @@ def test_select_carries_options_and_write_fn():
         options=("voice", "tone", "mute"),
         write_fn=lambda p, rep: (["settings", "sound", "mode", "vs", "0"], {"mode": p}),
     )
+    assert d.write_fn is not None
     assert d.write_fn("tone", {}) == (["settings", "sound", "mode", "vs", "0"], {"mode": "tone"})
diff --git a/tests/test_entity.py b/tests/test_entity.py
index b6c22f1..f0c0b9b 100644
--- a/tests/test_entity.py
+++ b/tests/test_entity.py
@@ -8,6 +8,9 @@ entity there would silently drop working sensors on first-poll timing,
 not just fix phantom ones.
 """
 
+from typing import cast
+
+from custom_components.localthings.coordinator import LocalThingsCoordinator
 from custom_components.localthings.entity import _is_included
 from custom_components.localthings.registry.capability import Capability
 from custom_components.localthings.registry.discovery import BoundEntity
@@ -27,6 +30,10 @@ class _FakeCoordinator:
         return self.last_resources
 
 
+def _coord(last_resources) -> LocalThingsCoordinator:
+    return cast(LocalThingsCoordinator, _FakeCoordinator(last_resources))
+
+
 def _bound(desc, href):
     capability = Capability(href=href, entities=(desc,))
     return BoundEntity(href=href, capability=capability, desc=desc)
@@ -40,17 +47,17 @@ class TestDefaultFieldGate:
 
     def test_included_when_field_present(self):
         bound = self._bound()
-        coord = _FakeCoordinator({"/x/vs/0": {"x.com.samsung.da.value": "1"}})
+        coord = _coord({"/x/vs/0": {"x.com.samsung.da.value": "1"}})
         assert _is_included(bound, coord) is True
 
     def test_excluded_when_field_absent_from_populated_rep(self):
         bound = self._bound()
-        coord = _FakeCoordinator({"/x/vs/0": {"x.com.samsung.da.other": "1"}})
+        coord = _coord({"/x/vs/0": {"x.com.samsung.da.other": "1"}})
         assert _is_included(bound, coord) is False
 
     def test_included_on_true_stub(self):
         bound = self._bound()
-        coord = _FakeCoordinator({"/x/vs/0": {"href": "/x/vs/0"}})
+        coord = _coord({"/x/vs/0": {"href": "/x/vs/0"}})
         assert _is_included(bound, coord) is True
 
     def test_included_on_genuinely_empty_rep(self):
@@ -60,12 +67,12 @@ class TestDefaultFieldGate:
         exists_fn (e.g. common.ENERGY_METER) opts into excluding on
         confirmed-empty, after verifying that's actually safe for its field."""
         bound = self._bound()
-        coord = _FakeCoordinator({"/x/vs/0": {}})
+        coord = _coord({"/x/vs/0": {}})
         assert _is_included(bound, coord) is True
 
     def test_excluded_when_href_missing_from_resources(self):
         bound = self._bound()
-        coord = _FakeCoordinator({})
+        coord = _coord({})
         assert _is_included(bound, coord) is False
 
 
@@ -77,9 +84,9 @@ class TestExplicitExistsFnGate:
             exists_fn=lambda rep, resources: rep.get("flag") is True,
         )
         bound = _bound(desc, "/x/vs/0")
-        coord = _FakeCoordinator({"/x/vs/0": {"flag": True}})
+        coord = _coord({"/x/vs/0": {"flag": True}})
         assert _is_included(bound, coord) is True
-        coord = _FakeCoordinator({"/x/vs/0": {"flag": False, "x.com.samsung.da.value": "1"}})
+        coord = _coord({"/x/vs/0": {"flag": False, "x.com.samsung.da.value": "1"}})
         assert _is_included(bound, coord) is False
 
 
@@ -87,5 +94,5 @@ class TestNoFieldEntities:
     def test_rep_fn_entity_always_included(self):
         desc = SensorDesc(key="x", rep_fn=lambda rep: rep.get("x.com.samsung.da.value"))
         bound = _bound(desc, "/x/vs/0")
-        coord = _FakeCoordinator({"/x/vs/0": {}})
+        coord = _coord({"/x/vs/0": {}})
         assert _is_included(bound, coord) is True
diff --git a/tests/test_identity.py b/tests/test_identity.py
index 4eed27e..654e0c7 100644
--- a/tests/test_identity.py
+++ b/tests/test_identity.py
@@ -71,8 +71,12 @@ def test_read_identity_keeps_raw_payloads_for_diagnostics():
         }
     )
     ident = read_identity(sess, serial=None)
-    assert ident.raw["/oic/p"]["mnmo"] == "RF9000B"
-    assert ident.raw["/oic/d"]["di"] == "abc-123"
+    oic_p = ident.raw["/oic/p"]
+    assert isinstance(oic_p, dict)
+    assert oic_p["mnmo"] == "RF9000B"
+    oic_d = ident.raw["/oic/d"]
+    assert isinstance(oic_d, dict)
+    assert oic_d["di"] == "abc-123"
 
 
 def test_read_identity_captures_oic_res_links():
diff --git a/tests/test_laundry_capabilities.py b/tests/test_laundry_capabilities.py
index 0bf5a3c..82b359e 100644
--- a/tests/test_laundry_capabilities.py
+++ b/tests/test_laundry_capabilities.py
@@ -1,6 +1,7 @@
 """Tests for the shared laundry capabilities (washer/dryer/dishwasher)."""
 
 from custom_components.localthings.registry.capabilities import laundry
+from custom_components.localthings.registry.entities import SelectDesc
 
 
 class TestCourseHelpers:
@@ -261,14 +262,22 @@ class TestBuzzerSound:
         assert laundry.BUZZER_SOUND.href == "/buzzersound/vs/0"
 
     def test_buzzer_sound_write(self):
-        desc = next(e for e in laundry.BUZZER_SOUND.entities if e.key == "buzzer_sound")
+        desc = next(
+            e
+            for e in laundry.BUZZER_SOUND.entities
+            if e.key == "buzzer_sound" and isinstance(e, SelectDesc)
+        )
         assert desc.options_field == "supportedBuzzerSound"
-        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 == ["buzzersound", "vs", "0"]
         assert body == {"setBuzzerSound": "On"}
 
     def test_finish_sound_exists_only_when_supported(self):
         desc = next(e for e in laundry.BUZZER_SOUND.entities if e.key == "finish_sound")
+        assert desc.exists_fn is not None
         assert desc.exists_fn({"setBuzzerSound": "On"}, {}) is False
         assert desc.exists_fn({"supportedFinishSound": ["FinishSound_1"]}, {}) is True
 
diff --git a/tests/test_laundry_writes.py b/tests/test_laundry_writes.py
index 4c9d891..11e9ce8 100644
--- a/tests/test_laundry_writes.py
+++ b/tests/test_laundry_writes.py
@@ -2,10 +2,12 @@
 
 from custom_components.localthings.registry.capabilities import laundry
 from custom_components.localthings.registry.capabilities.operational import OPERATIONAL_STATE
+from custom_components.localthings.registry.entities import ButtonDesc, SelectDesc, SwitchDesc
 
 
 def test_start_button_writes_run():
-    btn = next(e for e in OPERATIONAL_STATE.entities if e.key == "start")
+    btn = next(e for e in OPERATIONAL_STATE.entities if e.key == "start" and isinstance(e, ButtonDesc))
+    assert btn.write_fn is not None
     assert btn.write_fn("Run", {}) == (
         ["operational", "state", "vs", "0"],
         {"x.com.samsung.da.state": "Run"},
@@ -13,7 +15,8 @@ def test_start_button_writes_run():
 
 
 def test_pause_button_writes_pause():
-    btn = next(e for e in OPERATIONAL_STATE.entities if e.key == "pause")
+    btn = next(e for e in OPERATIONAL_STATE.entities if e.key == "pause" and isinstance(e, ButtonDesc))
+    assert btn.write_fn is not None
     assert btn.write_fn("Pause", {}) == (
         ["operational", "state", "vs", "0"],
         {"x.com.samsung.da.state": "Pause"},
@@ -21,7 +24,8 @@ def test_pause_button_writes_pause():
 
 
 def test_stop_button_writes_ready():
-    btn = next(e for e in OPERATIONAL_STATE.entities if e.key == "stop")
+    btn = next(e for e in OPERATIONAL_STATE.entities if e.key == "stop" and isinstance(e, ButtonDesc))
+    assert btn.write_fn is not None
     assert btn.write_fn("Ready", {}) == (
         ["operational", "state", "vs", "0"],
         {"x.com.samsung.da.state": "Ready"},
@@ -29,7 +33,8 @@ def test_stop_button_writes_ready():
 
 
 def test_sound_mode_write_valid():
-    desc = next(e for e in laundry.SOUND_MODE.entities if e.key == "sound_mode")
+    desc = next(e for e in laundry.SOUND_MODE.entities if e.key == "sound_mode" and isinstance(e, SelectDesc))
+    assert desc.write_fn is not None
     assert desc.write_fn("mute", {}) == (
         ["settings", "sound", "mode", "vs", "0"],
         {"mode": "mute"},
@@ -38,7 +43,10 @@ def test_sound_mode_write_valid():
 
 
 def test_led_brightness_write_valid():
-    desc = next(e for e in laundry.DOOR_LED.entities if e.key == "led_brightness")
+    desc = next(
+        e for e in laundry.DOOR_LED.entities if e.key == "led_brightness" and isinstance(e, SelectDesc)
+    )
+    assert desc.write_fn is not None
     assert desc.write_fn("Low", {}) == (
         ["doorled", "light", "vs", "0"],
         {"setBrightness": "Low"},
@@ -47,7 +55,10 @@ def test_led_brightness_write_valid():
 
 
 def test_led_night_light_write_valid():
-    desc = next(e for e in laundry.DOOR_LED.entities if e.key == "led_night_light")
+    desc = next(
+        e for e in laundry.DOOR_LED.entities if e.key == "led_night_light" and isinstance(e, SwitchDesc)
+    )
+    assert desc.write_fn is not None
     assert desc.write_fn("On", {}) == (
         ["doorled", "light", "vs", "0"],
         {"setNightLight": "On"},
diff --git a/tests/test_operational_capability.py b/tests/test_operational_capability.py
index 9520d67..0124b3d 100644
--- a/tests/test_operational_capability.py
+++ b/tests/test_operational_capability.py
@@ -1,6 +1,7 @@
 """Unit tests for operational state capabilities."""
 
 from custom_components.localthings.registry.capabilities.operational import OPERATIONAL_STATE
+from custom_components.localthings.registry.entities import NumberDesc
 
 
 def test_machine_state_maps_samsung_to_ocf():
@@ -17,11 +18,13 @@ class TestProgressPercentage:
 
     def test_zeroed_when_not_active(self):
         desc = next(e for e in OPERATIONAL_STATE.entities if e.key == "progress_percentage")
+        assert desc.rep_fn is not None
         rep = {"x.com.samsung.da.state": "Ready", "x.com.samsung.da.progressPercentage": "1"}
         assert desc.rep_fn(rep) == 0
 
     def test_passes_through_when_active(self):
         desc = next(e for e in OPERATIONAL_STATE.entities if e.key == "progress_percentage")
+        assert desc.rep_fn is not None
         rep = {"x.com.samsung.da.state": "Run", "x.com.samsung.da.progressPercentage": "42"}
         assert desc.rep_fn(rep) == 42
 
@@ -31,6 +34,7 @@ class TestCompletionMinutes:
 
     def test_completion_minutes_parsing(self):
         desc = next(e for e in OPERATIONAL_STATE.entities if e.key == "completion_minutes")
+        assert desc.rep_fn is not None
 
         # 1 hour 25 mins 30 secs -> 85 mins + 1 sec ceiling = 86 mins
         rep = {"x.com.samsung.da.remainingTime": "01:25:30"}
@@ -42,6 +46,7 @@ class TestCompletionMinutes:
 
     def test_completion_minutes_fallback_key(self):
         desc = next(e for e in OPERATIONAL_STATE.entities if e.key == "completion_minutes")
+        assert desc.rep_fn is not None
         rep = {"remainingTime": "00:45:00"}
         assert desc.rep_fn(rep) == 45
 
@@ -49,6 +54,7 @@ class TestCompletionMinutes:
         """Firmware freezes remainingTime at '00:01:00' when progress reaches 'Finish'.
         Should return 0 to prevent stuck values."""
         desc = next(e for e in OPERATIONAL_STATE.entities if e.key == "completion_minutes")
+        assert desc.rep_fn is not None
         rep = {
             "x.com.samsung.da.progress": "Finish",
             "x.com.samsung.da.remainingTime": "00:01:00",
@@ -57,6 +63,7 @@ class TestCompletionMinutes:
 
     def test_completion_minutes_missing_or_invalid(self):
         desc = next(e for e in OPERATIONAL_STATE.entities if e.key == "completion_minutes")
+        assert desc.rep_fn is not None
 
         rep = {}
         assert desc.rep_fn(rep) is None
@@ -71,6 +78,7 @@ class TestFinishTime:
 
     def test_seconds_and_microseconds_are_zeroed(self):
         desc = next(e for e in OPERATIONAL_STATE.entities if e.key == "finish_time")
+        assert desc.rep_fn is not None
         rep = {
             "x.com.samsung.da.state": "Run",
             "x.com.samsung.da.remainingTime": "00:29:00",
@@ -81,6 +89,7 @@ class TestFinishTime:
 
     def test_stable_across_polls_within_same_minute(self):
         desc = next(e for e in OPERATIONAL_STATE.entities if e.key == "finish_time")
+        assert desc.rep_fn is not None
         rep = {
             "x.com.samsung.da.state": "Run",
             "x.com.samsung.da.remainingTime": "00:29:00",
@@ -97,6 +106,7 @@ class TestDelayFieldFallback:
         )
 
         desc = next(e for e in OPERATIONAL_STATE.entities if e.key == "delay_start_hours")
+        assert desc.rep_fn is not None
         rep = {"x.com.samsung.da.delayEndTime": "02:30:00"}
         assert desc.rep_fn(rep) == 2.5
 
@@ -106,6 +116,7 @@ class TestDelayFieldFallback:
         )
 
         desc = next(e for e in OPERATIONAL_STATE.entities if e.key == "delay_start_hours")
+        assert desc.rep_fn is not None
         rep = {
             "x.com.samsung.da.delayStartTime": "01:00:00",
             "x.com.samsung.da.delayEndTime": "02:00:00",
@@ -117,9 +128,16 @@ class TestDelayFieldFallback:
             OPERATIONAL_STATE,
         )
 
-        desc = next(e for e in OPERATIONAL_STATE.entities if e.key == "delay_start_hours")
+        desc = next(
+            e
+            for e in OPERATIONAL_STATE.entities
+            if e.key == "delay_start_hours" and isinstance(e, NumberDesc)
+        )
+        assert desc.write_fn is not None
         rep = {"x.com.samsung.da.delayEndTime": "00:00:00"}
-        path, body = desc.write_fn(1.5, rep)
+        result = desc.write_fn(1.5, rep)
+        assert result is not None
+        path, body = result
         assert path == ["operational", "state", "vs", "0"]
         assert body == {"x.com.samsung.da.delayEndTime": "1:30:00"}
 
@@ -128,7 +146,14 @@ class TestDelayFieldFallback:
             OPERATIONAL_STATE,
         )
 
-        desc = next(e for e in OPERATIONAL_STATE.entities if e.key == "delay_start_hours")
+        desc = next(
+            e
+            for e in OPERATIONAL_STATE.entities
+            if e.key == "delay_start_hours" and isinstance(e, NumberDesc)
+        )
+        assert desc.write_fn is not None
         rep = {"x.com.samsung.da.delayStartTime": "00:00:00"}
-        _path, body = desc.write_fn(1.5, rep)
+        result = desc.write_fn(1.5, rep)
+        assert result is not None
+        _path, body = result
         assert body == {"x.com.samsung.da.delayStartTime": "1:30:00"}
diff --git a/tests/test_range_capabilities.py b/tests/test_range_capabilities.py
index 1bd3633..10f87f3 100644
--- a/tests/test_range_capabilities.py
+++ b/tests/test_range_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 range as range_caps
 from custom_components.localthings.registry.discovery import discover
+from custom_components.localthings.registry.entities import SelectDesc, SensorDesc, SwitchDesc
 from tests.conftest import _load_device
 
 
@@ -68,14 +69,21 @@ def test_unreported_burners_gated_out():
 
 
 def test_burner_power_level_write_is_read_modify_write():
-    desc = next(e for e in range_caps.COOKTOP_STATUS.entities if e.key == "burner_1_power_level")
+    desc = next(
+        e
+        for e in range_caps.COOKTOP_STATUS.entities
+        if e.key == "burner_1_power_level" and isinstance(e, SelectDesc)
+    )
     rep = {
         "burnerList": [
             {"burnerNumber": 0, "powerLevel": "3"},
             {"burnerNumber": 1, "powerLevel": "0"},
         ]
     }
-    path, body = desc.write_fn("boost", rep)
+    assert desc.write_fn is not None
+    result = desc.write_fn("boost", rep)
+    assert result is not None
+    path, body = result
     assert path == ["cooktop", "status", "vs", "0"]
     burners = {b["burnerNumber"]: b["powerLevel"] for b in body["burnerList"]}
     assert burners[1] == "boost"
@@ -83,8 +91,13 @@ def test_burner_power_level_write_is_read_modify_write():
 
 
 def test_burner_power_level_write_rejects_missing_burner():
-    desc = next(e for e in range_caps.COOKTOP_STATUS.entities if e.key == "burner_2_power_level")
+    desc = next(
+        e
+        for e in range_caps.COOKTOP_STATUS.entities
+        if e.key == "burner_2_power_level" and isinstance(e, SelectDesc)
+    )
     rep = {"burnerList": [{"burnerNumber": 0, "powerLevel": "0"}]}
+    assert desc.write_fn is not None
     assert desc.write_fn("5", rep) is None
 
 
@@ -109,17 +122,29 @@ def test_cooktop_power_is_read_only():  # issue #86
 
 
 def test_cooktop_child_lock_write():  # issue #86
-    desc = next(e for e in range_caps.COOKTOP_STATUS.entities if e.key == "cooktop_child_lock")
+    desc = next(
+        e
+        for e in range_caps.COOKTOP_STATUS.entities
+        if e.key == "cooktop_child_lock" and 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 == ["cooktop", "status", "vs", "0"]
     assert body == {"childLock": "on"}
     assert desc.write_fn("Bogus", {}) is None
 
 
 def test_probe_status_temperature_unit_reads_live_field():  # issue #86
-    desc = next(e for e in range_caps.PROBE_STATUS.entities if e.key == "probe_temperature")
+    desc = next(
+        e
+        for e in range_caps.PROBE_STATUS.entities
+        if e.key == "probe_temperature" and isinstance(e, SensorDesc)
+    )
+    assert desc.unit_fn is not None
     assert desc.unit_fn({"temperatureUnit": "C"}) == "°C"
     assert desc.unit_fn({"temperatureUnit": "F"}) == "°F"
     assert desc.unit_fn({}) == "°C"
diff --git a/tests/test_select_options.py b/tests/test_select_options.py
index 54be04c..954e589 100644
--- a/tests/test_select_options.py
+++ b/tests/test_select_options.py
@@ -3,8 +3,9 @@
 and callable forms of SelectDesc.options.
 """
 
-from typing import ClassVar
+from typing import ClassVar, cast
 
+from custom_components.localthings.coordinator import LocalThingsCoordinator
 from custom_components.localthings.registry.capability import Capability
 from custom_components.localthings.registry.discovery import BoundEntity
 from custom_components.localthings.registry.entities import SelectDesc
@@ -27,7 +28,7 @@ class _FakeCoordinator:
 def _make_select(desc, href, last_resources):
     capability = Capability(href=href, entities=(desc,))
     bound = BoundEntity(href=href, capability=capability, desc=desc)
-    return LocalThingsSelect(_FakeCoordinator(last_resources), bound)
+    return LocalThingsSelect(cast(LocalThingsCoordinator, _FakeCoordinator(last_resources)), bound)
 
 
 def test_static_options_unaffected():
@@ -107,7 +108,7 @@ async def test_unknown_vendor_option_round_trips_to_exact_raw_value():
     capability = Capability(href="/x/vs/0", entities=(desc,))
     bound = BoundEntity(href="/x/vs/0", capability=capability, desc=desc)
     coordinator = _WritableCoordinator({})
-    entity = LocalThingsSelect(coordinator, bound)
+    entity = LocalThingsSelect(cast(LocalThingsCoordinator, coordinator), bound)
 
     assert entity.options[-1] == "Future Vendor Mode"
     await entity.async_select_option("Future Vendor Mode")
diff --git a/tests/test_sensor_hysteresis.py b/tests/test_sensor_hysteresis.py
index 0f9145f..e4b5794 100644
--- a/tests/test_sensor_hysteresis.py
+++ b/tests/test_sensor_hysteresis.py
@@ -3,8 +3,10 @@
 from __future__ import annotations
 
 from datetime import UTC, datetime, timedelta
+from typing import cast
 
 from custom_components.localthings.const import CONF_FINISH_TIME_HYSTERESIS_MINUTES
+from custom_components.localthings.coordinator import LocalThingsCoordinator
 from custom_components.localthings.registry.capabilities.operational import OPERATIONAL_STATE
 from custom_components.localthings.registry.discovery import BoundEntity
 from custom_components.localthings.sensor import LocalThingsSensor
@@ -32,12 +34,14 @@ class _FakeCoordinator:
 
 def _sensor(threshold_minutes=3):
     coordinator = _FakeCoordinator(threshold_minutes)
+    href = OPERATIONAL_STATE.href
+    assert href is not None
     bound = BoundEntity(
-        href=OPERATIONAL_STATE.href,
+        href=href,
         capability=OPERATIONAL_STATE,
         desc=_FINISH_TIME_DESC,
     )
-    sensor = LocalThingsSensor(coordinator, bound)
+    sensor = LocalThingsSensor(cast(LocalThingsCoordinator, coordinator), bound)
     return sensor, coordinator
 
 
@@ -92,12 +96,14 @@ def test_non_hysteresis_sensor_is_unaffected():
     """A SensorDesc without hysteresis=True reads straight through, unchanged."""
     machine_state_desc = next(e for e in OPERATIONAL_STATE.entities if e.key == "machine_state")
     coordinator = _FakeCoordinator(threshold_minutes=3)
+    href = OPERATIONAL_STATE.href
+    assert href is not None
     bound = BoundEntity(
-        href=OPERATIONAL_STATE.href,
+        href=href,
         capability=OPERATIONAL_STATE,
         desc=machine_state_desc,
     )
-    sensor = LocalThingsSensor(coordinator, bound)
+    sensor = LocalThingsSensor(cast(LocalThingsCoordinator, coordinator), bound)
 
     coordinator.data = {"machine_state": "active"}
     assert sensor.native_value == "active"
diff --git a/tests/test_subdevice_discovery.py b/tests/test_subdevice_discovery.py
index ca54d9f..c839c2c 100644
--- a/tests/test_subdevice_discovery.py
+++ b/tests/test_subdevice_discovery.py
@@ -8,8 +8,11 @@ together, including device_info_for/via_device and the "no phantom
 
 from __future__ import annotations
 
+from typing import Any, cast
+
 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,
@@ -52,7 +55,7 @@ async def _discover_with(
     without the polling/reconnect machinery around it -- see coordinator.py's
     _enumerate_subdevices_blocking/_run_discovery. `_discover` below is the
     fixture-file-backed convenience wrapper most tests want."""
-    coordinator._session = FakeCoapSession(seeds)
+    coordinator._session = cast(DtlsCoapSession, FakeCoapSession(seeds))
     # _connect_session (skipped here -- the session is pre-set) is what
     # normally populates _identity via read_identity; set it directly with
     # the fixture's real /oic/res so enumeration sees the same links a live
@@ -88,7 +91,7 @@ async def _discover(coordinator: LocalThingsCoordinator, name: str) -> None:
     await _discover_with(coordinator, resources, oic_res, seeds)
 
 
-def _climate_bound(coordinator, subdevice_key: str):
+def _climate_bound(coordinator, subdevice_key: str | None):
     from custom_components.localthings.registry.subdevices import MAIN
 
     for b in coordinator.bound:
@@ -369,12 +372,16 @@ async def test_flat_subdevice_materializes_and_repolls_end_to_end(hass: HomeAssi
     # Re-poll: a fresh reading under the prefix should reach
     # canonical_resources through _poll_subdevice_seed's flat-mode branch,
     # not just sit frozen at the one-time enumeration snapshot.
-    coordinator._session.seeds[f"/{_SUB_UUID}/temperature/current/0"] = {
+    # FakeCoapSession's `seeds` is typed `dict[str, list]` for the common
+    # batch-list shape, but (per its own docstring) also legitimately holds
+    # plain Property maps for probe-style hrefs like these two.
+    seeds_map = cast("dict[str, Any]", cast(FakeCoapSession, coordinator._session).seeds)
+    seeds_map[f"/{_SUB_UUID}/temperature/current/0"] = {
         "range": [18.0, 30.0],
         "units": "C",
         "temperature": 27.5,
     }
-    coordinator._session.seeds[f"/{_SUB_UUID}/option/autoclean/vs/0"] = {
+    seeds_map[f"/{_SUB_UUID}/option/autoclean/vs/0"] = {
         "x.com.samsung.da.settingStatus": "On",
     }
     refreshed = coordinator._poll_subdevice_seed(subdevice)
@@ -437,7 +444,7 @@ def test_poll_subdevice_seed_collection_mode_unaffected_by_flat_fallback(
             ],
         }
     )
-    coordinator._session = sess
+    coordinator._session = cast(DtlsCoapSession, sess)
     subdevice = Subdevice(kind="prefixed", key=_SUB_UUID, seed_path=(_SUB_UUID, "device", "0"))
 
     result = coordinator._poll_subdevice_seed(subdevice)
@@ -463,7 +470,7 @@ def test_poll_subdevice_seed_flat_mode_polls_each_href_individually(
             # (_SUB_UUID, 'power', 'vs', '0') deliberately absent -> drops out.
         }
     )
-    coordinator._session = sess
+    coordinator._session = cast(DtlsCoapSession, sess)
     subdevice = Subdevice(
         kind="prefixed",
         key=_SUB_UUID,
@@ -496,7 +503,7 @@ def test_poll_subdevice_seed_flat_mode_skips_hrefs_covered_by_hot_warm_subpolls(
             (_SUB_UUID, "power", "vs", "0"): {"power": "On"},
         }
     )
-    coordinator._session = sess
+    coordinator._session = cast(DtlsCoapSession, sess)
     coordinator._warm_hrefs = [f"/{_SUB_UUID}/mode/vs/0"]
     subdevice = Subdevice(
         kind="prefixed",
@@ -528,10 +535,19 @@ async def test_multidevice_probe_never_reaches_discovery_or_the_cache(
     """
     resources, _oic, _seeds = _load_device_full("washer_flexwash")
     coordinator = _coordinator(hass)
-    coordinator._session = FakeCoapSession(
-        {
-            "/multidevice/vs/0": {"x.com.samsung.da.numofsubdevice": "2"},
-        }
+    # /multidevice/vs/0 here is a plain Property map, not a batch list -- see
+    # FakeCoapSession's own docstring on the two shapes its `seeds` values can
+    # take; its `seeds` param type only names the more common (list) shape.
+    coordinator._session = cast(
+        DtlsCoapSession,
+        FakeCoapSession(
+            cast(
+                "dict[str, list]",
+                {
+                    "/multidevice/vs/0": {"x.com.samsung.da.numofsubdevice": "2"},
+                },
+            )
+        ),
     )
     coordinator._identity = DeviceIdentity(
         manufacturer="Samsung Electronics",
diff --git a/tests/test_subdevices.py b/tests/test_subdevices.py
index 4074a59..1ee6690 100644
--- a/tests/test_subdevices.py
+++ b/tests/test_subdevices.py
@@ -6,8 +6,11 @@ UUID-prefixed tree) this module unifies.
 
 from __future__ import annotations
 
+from typing import cast
+
 import cbor2
 
+from custom_components.localthings.registry.by_type import DeviceRegistry
 from custom_components.localthings.registry.capability import Capability
 from custom_components.localthings.registry.entities import BinarySensorDesc, SensorDesc
 from custom_components.localthings.registry.subdevices import (
@@ -621,7 +624,7 @@ def test_discover_partitioned_main_pass_excludes_subdevice_hrefs_from_unbound():
     discover_partitioned(
         resources,
         [sub1],
-        lambda r, **_: reg,
+        lambda r, **_: cast(DeviceRegistry, reg),
         fallback_capabilities={},
         log=unbound.append,
     )
@@ -752,7 +755,7 @@ def test_discover_partitioned_no_subdevices_matches_plain_discover():
     bound_via_helper, _, materialized, skipped = discover_partitioned(
         resources,
         [],
-        lambda r, **_: reg,
+        lambda r, **_: cast(DeviceRegistry, reg),
         fallback_capabilities={},
     )
     bound_direct = discover(resources, reg.capabilities, reg.pattern_capabilities)
@@ -789,7 +792,7 @@ def test_discover_partitioned_skips_candidate_with_no_live_primary_entity():
     bound, _, materialized, skipped = discover_partitioned(
         resources,
         [unit2],
-        lambda r, **_: reg,
+        lambda r, **_: cast(DeviceRegistry, reg),
         fallback_capabilities={},
     )
     assert materialized == []
@@ -828,7 +831,7 @@ def test_discover_partitioned_materializes_candidate_with_live_primary_entity():
     bound, _, materialized, skipped = discover_partitioned(
         resources,
         [sub1],
-        lambda r, **_: reg,
+        lambda r, **_: cast(DeviceRegistry, reg),
         fallback_capabilities={},
     )
     assert materialized == [sub1]
@@ -871,7 +874,7 @@ def test_discover_partitioned_skips_candidate_whose_only_live_primary_is_a_meter
     bound, _, materialized, skipped = discover_partitioned(
         resources,
         [unit1],
-        lambda r, **_: reg,
+        lambda r, **_: cast(DeviceRegistry, reg),
         fallback_capabilities={},
     )
     assert materialized == []
@@ -910,7 +913,7 @@ def test_discover_partitioned_meter_carve_out_does_not_gate_out_a_live_subdevice
     bound, _, materialized, skipped = discover_partitioned(
         resources,
         [unit1],
-        lambda r, **_: reg,
+        lambda r, **_: cast(DeviceRegistry, reg),
         fallback_capabilities={},
     )
     assert materialized == [unit1]
@@ -938,7 +941,7 @@ def test_discover_partitioned_skipped_candidate_contributes_no_hot_warm_hrefs():
     discover_partitioned(
         resources,
         [unit2],
-        lambda r, **_: reg,
+        lambda r, **_: cast(DeviceRegistry, reg),
         fallback_capabilities={},
         tier_log=lambda href, tier: tiers.append(href),
     )
diff --git a/tests/test_washer_capabilities.py b/tests/test_washer_capabilities.py
index 519c1a0..2582ed1 100644
--- a/tests/test_washer_capabilities.py
+++ b/tests/test_washer_capabilities.py
@@ -8,6 +8,7 @@ fallback pairs and the energy meter in test_common_capabilities.py.
 from datetime import UTC
 
 from custom_components.localthings.registry.capabilities import laundry, washer
+from custom_components.localthings.registry.entities import SelectDesc
 
 
 def _rep_by_href(cap, href):
@@ -20,25 +21,50 @@ class TestWasherSettings:
         assert washer.WASHER_SETTINGS.href == "/washer/vs/0"
 
     def test_wash_temperature_read(self):
-        desc = next(e for e in washer.WASHER_SETTINGS.entities if e.key == "wash_temperature")
+        desc = next(
+            e
+            for e in washer.WASHER_SETTINGS.entities
+            if e.key == "wash_temperature" and isinstance(e, SelectDesc)
+        )
         assert desc.field == "x.com.samsung.da.waterTemperature"
         assert desc.options_field == "x.com.samsung.da.supportedWaterTemperature"
 
     def test_wash_temperature_write(self):
-        desc = next(e for e in washer.WASHER_SETTINGS.entities if e.key == "wash_temperature")
-        path, body = desc.write_fn("60", {})
+        desc = next(
+            e
+            for e in washer.WASHER_SETTINGS.entities
+            if e.key == "wash_temperature" and isinstance(e, SelectDesc)
+        )
+        assert desc.write_fn is not None
+        result = desc.write_fn("60", {})
+        assert result is not None
+        path, body = result
         assert path == ["washer", "vs", "0"]
         assert body == {"x.com.samsung.da.waterTemperature": "60"}
 
     def test_spin_speed_write(self):
-        desc = next(e for e in washer.WASHER_SETTINGS.entities if e.key == "spin_speed")
-        path, body = desc.write_fn("1400", {})
+        desc = next(
+            e
+            for e in washer.WASHER_SETTINGS.entities
+            if e.key == "spin_speed" and isinstance(e, SelectDesc)
+        )
+        assert desc.write_fn is not None
+        result = desc.write_fn("1400", {})
+        assert result is not None
+        path, body = result
         assert path == ["washer", "vs", "0"]
         assert body == {"x.com.samsung.da.spinLevel": "1400"}
 
     def test_rinse_cycles_write(self):
-        desc = next(e for e in washer.WASHER_SETTINGS.entities if e.key == "rinse_cycles")
-        path, body = desc.write_fn("3", {})
+        desc = next(
+            e
+            for e in washer.WASHER_SETTINGS.entities
+            if e.key == "rinse_cycles" and 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 == ["washer", "vs", "0"]
         assert body == {"x.com.samsung.da.rinseCycles": "3"}
 
@@ -49,12 +75,20 @@ class TestDryLevel:
 
     def test_exists_only_when_supported_dry_level_present(self):
         desc = next(e for e in washer.WASHER_SETTINGS.entities if e.key == "dry_level")
+        assert desc.exists_fn is not None
         assert desc.exists_fn({"x.com.samsung.da.supportedDryLevel": ["None", "30"]}, {}) is True
         assert desc.exists_fn({}, {}) is False
 
     def test_write(self):
-        desc = next(e for e in washer.WASHER_SETTINGS.entities if e.key == "dry_level")
-        path, body = desc.write_fn("Cupboard", {})
+        desc = next(
+            e
+            for e in washer.WASHER_SETTINGS.entities
+            if e.key == "dry_level" and isinstance(e, SelectDesc)
+        )
+        assert desc.write_fn is not None
+        result = desc.write_fn("Cupboard", {})
+        assert result is not None
+        path, body = result
         assert path == ["washer", "vs", "0"]
         assert body == {"x.com.samsung.da.dryLevel": "Cupboard"}
 
@@ -82,15 +116,21 @@ class TestWasherCourse:
         translations/en.json via translation_key, not Python (see select.py's
         _display())."""
         desc = next(e for e in washer.WASHER_COURSE.entities if e.key == "cycle")
+        assert desc.rep_fn is not None
         rep = {"x.com.samsung.da.options": ["DeviceType_0167", "Course_1C", "GMT_04"]}
         assert desc.rep_fn(rep) == "1C"
 
     def test_missing_course_option_returns_none(self):
         desc = next(e for e in washer.WASHER_COURSE.entities if e.key == "cycle")
+        assert desc.rep_fn is not None
         assert desc.rep_fn({"x.com.samsung.da.options": ["GMT_04"]}) is None
 
     def test_cycle_desc_uses_cycle_options_callable(self):
-        desc = next(e for e in washer.WASHER_COURSE.entities if e.key == "cycle")
+        desc = next(
+            e
+            for e in washer.WASHER_COURSE.entities
+            if e.key == "cycle" and isinstance(e, SelectDesc)
+        )
         assert desc.options is laundry.cycle_options
 
     def test_exists_only_when_edit_course_list_is_live(self):
@@ -98,6 +138,7 @@ class TestWasherCourse:
         when a device actually populates editCourseList (see
         _cycle_options's docstring for why MostUsed_ isn't used either)."""
         desc = next(e for e in washer.WASHER_COURSE.entities if e.key == "cycle")
+        assert desc.exists_fn is not None
         assert desc.exists_fn({}, {}) is False
         assert desc.exists_fn({}, {"/wm/editcourse/vs/0": {}}) is False
         live = {"/wm/editcourse/vs/0": {"x.com.samsung.da.editCourseList": "EditCourseList_1C"}}
@@ -107,9 +148,16 @@ class TestWasherCourse:
         """Confirmed on real hardware (issue #54): the write only needs to
         carry the changed token -- the device matches by prefix, evicts the
         stale token, and merges the result into the array itself."""
-        desc = next(e for e in washer.WASHER_COURSE.entities if e.key == "cycle")
+        desc = next(
+            e
+            for e in washer.WASHER_COURSE.entities
+            if e.key == "cycle" and isinstance(e, SelectDesc)
+        )
+        assert desc.write_fn is not None
         rep = {"x.com.samsung.da.options": ["DeviceType_0167", "Course_1C", "GMT_04"]}
-        path, body = desc.write_fn("1D", rep)
+        result = desc.write_fn("1D", rep)
+        assert result is not None
+        path, body = result
         assert path == ["course", "vs", "0"]
         assert body == {"x.com.samsung.da.options": ["Course_1D"]}
 
@@ -121,6 +169,7 @@ class TestDrumClean:
         desc = next(
             e for e in washer.WASHER_COURSE.entities if e.key == "drum_clean_cycles_remaining"
         )
+        assert desc.rep_fn is not None
         rep = {"x.com.samsung.da.options": ["WashingTimes_3", "DrumCleanProposal_40"]}
         assert desc.rep_fn(rep) == 37
 
@@ -128,6 +177,7 @@ class TestDrumClean:
         desc = next(
             e for e in washer.WASHER_COURSE.entities if e.key == "drum_clean_cycles_remaining"
         )
+        assert desc.rep_fn is not None
         rep = {"x.com.samsung.da.options": ["WashingTimes_50", "DrumCleanProposal_40"]}
         assert desc.rep_fn(rep) == 0
 
@@ -135,12 +185,14 @@ class TestDrumClean:
         desc = next(
             e for e in washer.WASHER_COURSE.entities if e.key == "drum_clean_cycles_remaining"
         )
+        assert desc.rep_fn is not None
         assert desc.rep_fn({"x.com.samsung.da.options": []}) is None
 
     def test_cycles_remaining_exists_only_when_computable(self):
         desc = next(
             e for e in washer.WASHER_COURSE.entities if e.key == "drum_clean_cycles_remaining"
         )
+        assert desc.exists_fn is not None
         assert desc.exists_fn({"x.com.samsung.da.options": []}, {}) is False
         rep = {"x.com.samsung.da.options": ["WashingTimes_3", "DrumCleanProposal_40"]}
         assert desc.exists_fn(rep, {}) is True
@@ -149,6 +201,7 @@ class TestDrumClean:
         """DrumCleanLog_2026-07-01T20:18:07 -> a UTC-aware datetime,
         matching the same screenshot's '10 days ago' (as of 2026-07-11)."""
         desc = next(e for e in washer.WASHER_COURSE.entities if e.key == "drum_clean_last_cleaned")
+        assert desc.rep_fn is not None
         rep = {"x.com.samsung.da.options": ["DrumCleanLog_2026-07-01T20:18:07"]}
         from datetime import datetime
 
@@ -156,7 +209,9 @@ class TestDrumClean:
 
     def test_last_cleaned_missing(self):
         desc = next(e for e in washer.WASHER_COURSE.entities if e.key == "drum_clean_last_cleaned")
+        assert desc.rep_fn is not None
         assert desc.rep_fn({"x.com.samsung.da.options": []}) is None
+        assert desc.exists_fn is not None
         assert desc.exists_fn({"x.com.samsung.da.options": []}, {}) is False