diff --git a/agent_assembly/core/runtime_interceptor.py b/agent_assembly/core/runtime_interceptor.py
index 4eb7ded..f3d3259 100644
--- a/agent_assembly/core/runtime_interceptor.py
+++ b/agent_assembly/core/runtime_interceptor.py
@@ -279,6 +279,13 @@ def check_tool_start(
             # proceed (fail open).
             return self._on_query_failure("runtime query failed")
 
+        # A non-dict result (e.g. ``None`` from a malformed/partial runtime
+        # response) is not an authoritative verdict; route it through the
+        # fail-closed path rather than raising ``AttributeError`` on ``.get``
+        # (AAASM-4167).
+        if not isinstance(result, dict):
+            return self._on_query_failure("runtime returned non-dict result")
+
         # No ``"allow"`` default: a missing / empty ``decision`` is not an
         # authoritative allow and must route through the fail-closed path below
         # under ``enforce`` (AAASM-4014).
diff --git a/test/unit/core/test_runtime_interceptor.py b/test/unit/core/test_runtime_interceptor.py
index d2c7603..9a1cb83 100644
--- a/test/unit/core/test_runtime_interceptor.py
+++ b/test/unit/core/test_runtime_interceptor.py
@@ -322,6 +322,40 @@ def test_observe_error_decision_still_fails_open(decision: str) -> None:
     assert result == {"status": "allow"}
 
 
+class _NonDictRuntimeClient:
+    """A runtime whose query_policy returns a non-dict (e.g. ``None``)."""
+
+    def __init__(self, result: Any) -> None:
+        self._result = result
+
+    def query_policy(self, *_args: Any, **_kwargs: Any) -> Any:
+        return self._result
+
+
+@pytest.mark.parametrize("bad_result", [None, "deny", 42, ["deny"]])
+def test_enforce_non_dict_return_fails_closed(bad_result: Any) -> None:
+    """AAASM-4167: a non-dict query_policy return denies under enforce rather
+    than raising AttributeError on ``result.get``."""
+    interceptor = RuntimeQueryInterceptor(
+        _FakeGatewayClient(), _NonDictRuntimeClient(bad_result), "agent-001", enforce=True
+    )
+
+    result = interceptor.check_tool_start(serialized={"name": "t"}, input_str="i")
+
+    assert result["status"] == "deny"
+
+
+@pytest.mark.parametrize("bad_result", [None, "deny", 42, ["deny"]])
+def test_observe_non_dict_return_fails_open(bad_result: Any) -> None:
+    """AAASM-4167: without enforce a non-dict return degrades to a clean allow,
+    not an AttributeError."""
+    interceptor = RuntimeQueryInterceptor(_FakeGatewayClient(), _NonDictRuntimeClient(bad_result), "agent-001")
+
+    result = interceptor.check_tool_start(serialized={"name": "t"}, input_str="i")
+
+    assert result == {"status": "allow"}
+
+
 def test_enforce_unreachable_runtime_denies_all(monkeypatch: pytest.MonkeyPatch) -> None:
     """AAASM-3106: native present but runtime unreachable yields a deny-all
     interceptor under enforce, not the fail-open bare client."""