Select the bmspy-ups device from the configured devices

bmspy-ups selected its device from the devices that had data at startup, and exited with status 0 if the selection failed. One failed first read ended the monitor or made it select the wrong device.

The server has a new DEVICES command that lists the configured names, and client.list_devices calls it. bmspy-ups selects from that list and then waits for the first data of its device. A wrong or missing --device now exits with status 2. The service file does not restart on that status, because a restart cannot correct it.

An older server ends on the unknown DEVICES command, so update the server first.

tests/test_server.py

@@ -445,6 +445,20 @@ class TestServerMain:
         finally:
             self._stop_server(sock_path, t)
 
+    def test_devices_command_lists_configured_devices(self, tmp_path):
+        """DEVICES names every configured device, through the real client."""
+        from bmspy import client
+
+        sock_path = str(tmp_path / "server_devices.sock")
+        ready = threading.Event()
+        t = self._make_server_thread(sock_path, ready, threading.Event())
+        t.start()
+        ready.wait(timeout=2)
+        try:
+            assert client.list_devices(sock_path, "test") == ["ttyUSB0"]
+        finally:
+            self._stop_server(sock_path, t)
+
     def test_deregister_command(self, tmp_path):
         """Test DEREGISTER command via server main()."""
         sock_path = str(tmp_path / "server_dereg.sock")