fix(transport): disable UART ESP-NOW bridge by default

Require serial_enabled true in settings to open serial_port; default false in
set_defaults for Wi-Fi-only and dev machines.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/models/transport.py

@@ -33,6 +33,13 @@ async def _to_thread(func, *args):
     return await loop.run_in_executor(None, func, *args)
 
 
+class NullSender:
+    """Used when no ESP-NOW UART bridge is configured or the port cannot be opened."""
+
+    async def send(self, data, addr=None):
+        return True
+
+
 class SerialSender:
     def __init__(self, port, baudrate, default_addr=None):
         import serial
@@ -62,7 +69,22 @@ def get_current_sender():
 
 
 def get_sender(settings):
+    # Serial ESP-NOW bridge is opt-in (serial_enabled true); default off for dev / Wi-Fi-only.
+    if not settings.get("serial_enabled"):
+        print("[startup] serial bridge disabled (set serial_enabled true in settings.json to enable)")
+        return NullSender()
     port = settings.get("serial_port", "/dev/ttyS0")
+    raw_port = str(port).strip() if port is not None else ""
+    if not raw_port or raw_port.lower() in ("none", "off"):
+        print("[startup] serial bridge disabled (empty serial_port)")
+        return NullSender()
     baudrate = settings.get("serial_baudrate", 912000)
     default_addr = settings.get("serial_destination_mac", "ffffffffffff")
-    return SerialSender(port, baudrate, default_addr=default_addr)
+    try:
+        return SerialSender(raw_port, baudrate, default_addr=default_addr)
+    except Exception as e:
+        print(
+            f"[startup] serial open failed ({raw_port!r}): {e}; "
+            "continuing without ESP-NOW bridge (Wi-Fi drivers unchanged)"
+        )
+        return NullSender()

src/settings.py

@@ -57,6 +57,9 @@ class Settings(dict):
         # down (0 disables). Helps drivers that reconnect after seeing traffic on 8766.
         if 'wifi_driver_hello_interval_s' not in self:
             self['wifi_driver_hello_interval_s'] = 10.0
+        # UART to ESP32 ESP-NOW bridge; default off (Wi-Fi drivers need no serial).
+        if 'serial_enabled' not in self:
+            self['serial_enabled'] = False
 
     def save(self):
         try: