refactor: normalize data directory naming, and consolidate serial connection handling

src/pygui/serialcomm/serial_port.py

@@ -45,6 +45,33 @@ class SerialPort:
     def __init__(self, port_name: str) -> None:
         self._port_name = port_name
 
+    # ------------------------------------------------------------------
+    # Port opening (shared between scoped and long-lived use)
+    # ------------------------------------------------------------------
+
+    @staticmethod
+    def open_port(port_name: str, timeout: float | None = None) -> pyserial.Serial:
+        """Open a serial port with baud-rate fallback.
+
+        Tries SerialPort.BAUDRATE first, falls back to 115200 on failure.
+        The caller owns the lifecycle of the returned Serial object."""
+        kwargs = dict(
+            parity=pyserial.PARITY_NONE,
+            bytesize=8,
+            stopbits=pyserial.STOPBITS_ONE,
+            xonxoff=False,
+            rtscts=False,
+            dsrdtr=False,
+        )
+        if timeout is not None:
+            kwargs["timeout"] = timeout
+
+        try:
+            return pyserial.Serial(port_name, SerialPort.BAUDRATE, **kwargs)
+        except Exception as exc:
+            log.warning("Baud rate %d failed on %s, falling back to 115200: %s", SerialPort.BAUDRATE, port_name, exc)
+            return pyserial.Serial(port_name, 115200, **kwargs)
+
     # ------------------------------------------------------------------
     # Context manager for scoped port access
     # ------------------------------------------------------------------
@@ -52,31 +79,7 @@ class SerialPort:
     @contextmanager
     def _open(self, timeout: float | None = None) -> Iterator[pyserial.Serial]:
         """Open the serial port, yield it, then close on exit."""
-        try:
-            port = pyserial.Serial(
-                self._port_name,
-                self.BAUDRATE,
-                parity=pyserial.PARITY_NONE,
-                bytesize=8,
-                stopbits=pyserial.STOPBITS_ONE,
-                xonxoff=False,
-                rtscts=False,
-                dsrdtr=False,
-            )
-        except Exception as exc:
-            log.warning("Baud rate %d failed on %s, falling back to 115200: %s", self.BAUDRATE, self._port_name, exc)
-            port = pyserial.Serial(
-                self._port_name,
-                115200,
-                parity=pyserial.PARITY_NONE,
-                bytesize=8,
-                stopbits=pyserial.STOPBITS_ONE,
-                xonxoff=False,
-                rtscts=False,
-                dsrdtr=False,
-            )
-        if timeout is not None:
-            port.timeout = timeout
+        port = self.open_port(self._port_name, timeout=timeout)
         try:
             yield port
         finally: