diff --git a/gateway/platforms/access_policy_mixin.py b/gateway/platforms/access_policy_mixin.py
index 5f1bff27aa..f73d27d139 100644
--- a/gateway/platforms/access_policy_mixin.py
+++ b/gateway/platforms/access_policy_mixin.py
@@ -24,6 +24,13 @@ OPTIN_TRUTHY = frozenset({"true", "1", "yes"})
 class OwnAccessPolicyMixin:
     ALLOW_ALL_ENV_PREFIX: str = ""
 
+    def __init_subclass__(cls, **kwargs):
+        super().__init_subclass__(**kwargs)
+        # A host that forgets its prefix would silently read ``_ALLOW_ALL_USERS`` and deny every
+        # open-DM deployment whose setup wrote ``<PLATFORM>_ALLOW_ALL_USERS`` — refuse at class creation.
+        if not str(cls.ALLOW_ALL_ENV_PREFIX or "").strip():
+            raise TypeError(f"{cls.__qualname__} mixes in OwnAccessPolicyMixin but sets no ALLOW_ALL_ENV_PREFIX")
+
     @property
     def enforces_own_access_policy(self) -> bool:
         return True
diff --git a/plugins/platforms/wecom/adapter.py b/plugins/platforms/wecom/adapter.py
index 572e5d0c92..98086b483d 100644
--- a/plugins/platforms/wecom/adapter.py
+++ b/plugins/platforms/wecom/adapter.py
@@ -101,6 +101,7 @@ def _content_of(container: Dict[str, Any], key: str) -> str:
 class WeComAdapter(WeComStreamMixin, WeComMediaMixin, ChatSendQueueMixin, OwnAccessPolicyMixin, BasePlatformAdapter):
     """WeCom AI Bot adapter backed by a persistent WebSocket connection."""
 
+    ALLOW_ALL_ENV_PREFIX = "WECOM"
     MAX_MESSAGE_LENGTH = MAX_MESSAGE_LENGTH
     SUPPORTS_MESSAGE_EDITING = False
     SUPPORTS_NATIVE_STREAMING = True  # msgtype "stream" via aibot_respond_msg, not edit-based
diff --git a/tests/gateway/test_access_policy_mixin.py b/tests/gateway/test_access_policy_mixin.py
index 54edaa7d40..292daae97b 100644
--- a/tests/gateway/test_access_policy_mixin.py
+++ b/tests/gateway/test_access_policy_mixin.py
@@ -60,21 +60,43 @@ def _verdicts(host, name, dm_policy, group_policy):
     return out
 
 
-@pytest.mark.parametrize("opt_in", [{}, {"GATEWAY_ALLOW_ALL_USERS": "true"}])
-def test_all_own_policy_adapters_agree(monkeypatch, opt_in):
-    for var in ("GATEWAY_ALLOW_ALL_USERS", "WEIXIN_ALLOW_ALL_USERS", "WECOM_ALLOW_ALL_USERS",
-                "QQ_ALLOW_ALL_USERS", "WHATSAPP_ALLOW_ALL_USERS", "YUANBAO_ALLOW_ALL_USERS"):
+# Per-host opt-in var (the one ``hermes gateway setup`` writes). Setting only GATEWAY_ALLOW_ALL_USERS
+# would pass with a host whose prefix is missing — that is exactly how WeCom regressed once.
+PLATFORM_OPT_IN = {"weixin": "WEIXIN_ALLOW_ALL_USERS", "wecom": "WECOM_ALLOW_ALL_USERS",
+                   "qqbot": "QQ_ALLOW_ALL_USERS", "whatsapp": "WHATSAPP_ALLOW_ALL_USERS",
+                   "yuanbao": "YUANBAO_ALLOW_ALL_USERS"}
+
+
+def _all_agree(hosts, opt_in_for, label):
+    for dm_policy, group_policy in itertools.product(POLICIES, POLICIES):
+        table = {}
+        for name, host in hosts.items():
+            with _scope(opt_in_for(name)):
+                table[name] = _verdicts(host, name, dm_policy, group_policy)
+        for name, verdicts in table.items():
+            assert verdicts == table["weixin"], (name, dm_policy, group_policy, label)
+        expected_open = bool(opt_in_for("weixin")) and dm_policy == "open"
+        assert table["weixin"][("dm", "stranger")] is expected_open
+        assert table["weixin"][("intake", "   ")] is False  # blank principal never admitted
+        assert table["weixin"][("intake", "stranger")] is (dm_policy == "pairing" or expected_open)
+
+
+@pytest.mark.parametrize("mode", ["none", "gateway", "platform"])
+def test_all_own_policy_adapters_agree(monkeypatch, mode):
+    for var in ("GATEWAY_ALLOW_ALL_USERS", *PLATFORM_OPT_IN.values()):
         monkeypatch.delenv(var, raising=False)
-    hosts = _hosts()
-    with _scope(opt_in):
-        for dm_policy, group_policy in itertools.product(POLICIES, POLICIES):
-            table = {name: _verdicts(host, name, dm_policy, group_policy) for name, host in hosts.items()}
-            for name, verdicts in table.items():
-                assert verdicts == table["weixin"], (name, dm_policy, group_policy, opt_in)
-            expected_open = bool(opt_in) and dm_policy == "open"
-            assert table["weixin"][("dm", "stranger")] is expected_open
-            assert table["weixin"][("intake", "   ")] is False  # blank principal never admitted
-            assert table["weixin"][("intake", "stranger")] is (dm_policy == "pairing" or expected_open)
+    opt_in_for = {
+        "none": lambda name: {},
+        "gateway": lambda name: {"GATEWAY_ALLOW_ALL_USERS": "true"},
+        "platform": lambda name: {PLATFORM_OPT_IN[name]: "true"},
+    }[mode]
+    _all_agree(_hosts(), opt_in_for, mode)
+
+
+def test_mixin_host_without_prefix_is_rejected_at_class_creation():
+    with pytest.raises(TypeError, match="ALLOW_ALL_ENV_PREFIX"):
+        class Host(OwnAccessPolicyMixin):  # noqa: F841
+            _dm_policy = "open"
 
 
 def test_platform_prefix_env_name_is_scoped_and_fail_closed(monkeypatch):