Address review: gate the AddWash master write on a readable mask

The master alarm switch wrote AddWashSet_7/_0 without consulting
_add_wash_mask, so a device reporting a wider mask (AddWashSet_15) or a
non-numeric one had it truncated to three bits -- the write that mask's
own docstring rules out, while the per-moment switches already refused it.

Also corrects the washer_ww6500 golden docstring: the fixture carries no
/oic/d and the test passes no device_types, so the device is typed solely
by the WW consumer prefix in its description. A51 is not a board token,
which makes that the fragile route worth naming.

tests/test_golden_regression.py

@@ -390,9 +390,12 @@ def test_registry_reproduces_golden_state_keys_for_washer_dryer_combo():
 
 
 def test_registry_reproduces_golden_state_keys_for_washer_ww6500():
-    """DA_WM_A51_20 front-loader, routed by /oic/d's oic.d.washer rather
-    than a board token. Reports the AddWash tokens and an empty
-    /wm/editcourse/vs/0, so its cycle list comes from supportedOptions."""
+    """DA_WM_A51_20 front-loader, typed solely by the WW consumer prefix in
+    its /information/vs/0 description: A51 is not a board token, so with the
+    description blanked this device resolves to nothing and drops to the
+    unknown-device fallback. That is the fragile route this test pins.
+    Reports the AddWash tokens and an empty /wm/editcourse/vs/0, so its cycle
+    list comes from supportedOptions."""
     from tests.conftest import _load_device
 
     resources = _load_device("washer_ww6500")

tests/test_washer_add_wash.py

@@ -86,6 +86,17 @@ class TestAlarmMasterSwitch:
         desc = _desc("add_wash_alarm", SwitchDesc)
         assert _write(desc, "On", {}) is None
 
+    @pytest.mark.parametrize("raw", ["15", "On", "-1"])
+    def test_refuses_to_write_over_a_mask_it_cannot_read(self, raw):
+        """A device reporting a wider mask must not have it truncated to 7.
+        The master is gated exactly like the per-moment writes, so an
+        unrecognized mask leaves every AddWash switch read-only."""
+        desc = _desc("add_wash_alarm", SwitchDesc)
+        rep = _rep(f"AddWashSet_{raw}")
+        assert desc.rep_fn(rep) is None
+        assert _write(desc, "On", rep) is None
+        assert _write(desc, "Off", rep) is None
+
 
 class TestAlarmMomentSwitches:
     @pytest.mark.parametrize("key,bit", BITS.items())
@@ -197,6 +208,17 @@ class TestAgainstTheWW6500Dump:
     """DA_WM_A51_20_COMMON_WW6500, captured with the alarm off, the course
     permitting all three moments and the lamp dark."""
 
+    def test_types_only_by_the_description_consumer_prefix(self):
+        """A51 is not a board token, so the WW prefix in the description is
+        the only thing routing this device -- see the golden test's docstring.
+        Pinned here so the claim can't quietly stop being true."""
+        from custom_components.localthings.registry.by_type import for_device_by_model
+
+        info = _load_device("washer_ww6500")["/information/vs/0"]
+        model = info["x.com.samsung.da.modelNum"]
+        assert for_device_by_model(model, info["x.com.samsung.da.description"]).name == "washer"
+        assert for_device_by_model(model, "") is None
+
     def test_no_unbound_hrefs(self):
         resources = _load_device("washer_ww6500")
         reg = resolve(resources)