Raise a clear client error for a refused request

socket_comms now raises DaemonError with the server message if the reply has the status ERROR. Before, the reply reached code that expects device data, and that code raised KeyError.

tests/test_client.py

@@ -91,6 +91,28 @@ class TestReadData:
             call_args = mock_comms.call_args[0][1]
             assert call_args.get("ups") == "myups"
 
+    @pytest.mark.parametrize("call", [
+        lambda client: client.list_devices("/fake/socket", "test"),
+        lambda client: client.read_data("/fake/socket", "test"),
+    ], ids=["list_devices", "read_data"])
+    def test_error_reply_raises_the_daemon_message(self, call):
+        """An ERROR reply must not reach the code that expects device data."""
+        from bmspy import client
+        reply = json.dumps({"status": "ERROR", "message": "unknown command: 'DEVICES'"}).encode()
+        sock = MagicMock()
+        sock.recv.side_effect = [struct.pack("!I", len(reply)), reply]
+        with patch("bmspy.client.socket.socket", return_value=sock):
+            with pytest.raises(client.DaemonError, match="unknown command: 'DEVICES'"):
+                call(client)
+        sock.close.assert_called()
+
+    def test_registration_logs_an_error_reply(self, capsys):
+        from bmspy import client
+        with patch("bmspy.client.socket_comms", side_effect=client.DaemonError("daemon refused 'REGISTER': no")), \
+             patch("bmspy.client.is_registered", False):
+            client.handle_registration("/fake/socket", "test")
+        assert "daemon refused 'REGISTER': no" in capsys.readouterr().out
+
     def test_list_devices_returns_configured_names(self):
         from bmspy.client import list_devices
         with patch("bmspy.client.socket_comms", return_value={"devices": ["network", "nas"]}) as mock_comms: