fix: Yaris 2013 OBD compatibility hardening

- _decode_odometer: catch all exceptions and return None instead of raising.
  PID 0xA6 (odometer) is not guaranteed on 2013 Toyota Yaris — a garbage
  response or unsupported PID previously raised ValueError through python-obd's
  decoder, which app_obd._query() caught and treated as a lost connection,
  killing the entire OBD session. Now it gracefully returns None.

- connect_obd: reset all sensor globals (rpm, coolant_temp, fuel_level,
  throttle_position, mil_on, dtc_codes, odometer, timestamps) on each new
  connection so the UI doesn't display stale readings from the previous
  ignition cycle while fresh polls are completing.

- yaris-obd.service: add commented OBD_PROTOCOL=6 hint for post-confirmation
  pinning (eliminates 3-5s auto-probe delay after first confirmed connection).

Co-authored-by: Copilot <[email protected]>

modules/app_obd.py

@@ -52,10 +52,13 @@ connection = None
 
 
 def _decode_odometer(messages):
-    data = messages[0].data[2:]
-    if len(data) != 4:
-        raise ValueError(f"expected 4 odometer bytes, received {len(data)}")
-    return int.from_bytes(bytes(data), byteorder="big") / 10
+    try:
+        data = messages[0].data[2:]
+        if len(data) != 4:
+            return None
+        return int.from_bytes(bytes(data), byteorder="big") / 10
+    except Exception:
+        return None
 
 
 ODOMETER_COMMAND = obd.OBDCommand(
@@ -225,6 +228,21 @@ def connect_obd():
             _emit_disconnected()
             return None
 
+        # Reset stale sensor values from the previous ignition cycle so the
+        # UI doesn't briefly display outdated readings before the first polls.
+        global rpm, coolant_temp, fuel_level, throttle_position, mil_on, dtc_codes, odometer
+        global mil_updated_at, dtc_updated_at, speed_updated_at
+        rpm = None
+        coolant_temp = None
+        fuel_level = None
+        throttle_position = None
+        mil_on = None
+        dtc_codes = []
+        odometer = None
+        mil_updated_at = None
+        dtc_updated_at = None
+        speed_updated_at = None
+
         _log_connection_diagnostics(candidate)
         app_events.socketio.emit("obd_status", obd_status[1])
         _start_polling_threads()