byd: fix canError ("Unknown Vehicle Variant") from strict parser alive checks

Explicit parser frequencies made canValid=False when state-dependent
messages are absent (PCM_BUTTONS is event-driven; MPC_LKAS_CMD/ACC_CMD
only flow when stock ADAS is active), tripping EventName.canError.

- Alive-check only control-critical messages, at a conservative 10Hz
  (1s timeout): ESC, BRAKE_APPLIED, PEDAL, STEER_MODULE, STEERING_TORQUE,
  DRIVE_STATE, ACC_HUD_ADAS
- Parse-but-don't-alive-check (nan) the rest: STALKS, METER_CLUSTER,
  MPC_LKAS_CMD, ACC_CMD
- PCM_BUTTONS is parsed on both pt and cam parsers (bus assignment is
  harness dependent); MADS reads LKAS_ON_BTN from whichever bus sees it

Verified: canValid=True with idle stock ADAS, LKAS button events work
from either bus, canValid stays True throughout.

opendbc_repo/opendbc/car/byd/carstate.py

@@ -100,23 +100,30 @@ class CarState(CarStateBase, MadsCarState):
 
   @staticmethod
   def get_can_parsers(CP, CP_SP):
+    # Frequencies are deliberately conservative (10x timeout forgiveness):
+    # only messages required for control are alive-checked, everything
+    # optional/state-dependent is parsed but not alive-checked (nan).
     pt_messages = [
       # sig_address, frequency
-      ("ESC", 50),
-      ("BRAKE_APPLIED", 50),
-      ("PEDAL", 50),
-      ("STEER_MODULE", 100),
-      ("STEERING_TORQUE", 50),
-      ("DRIVE_STATE", 50),
-      ("STALKS", 20),
-      ("METER_CLUSTER", 20),
-      ("PCM_BUTTONS", 20),
+      ("ESC", 10),
+      ("BRAKE_APPLIED", 10),
+      ("PEDAL", 10),
+      ("STEER_MODULE", 10),
+      ("STEERING_TORQUE", 10),
+      ("DRIVE_STATE", 10),
+      ("STALKS", float('nan')),
+      ("METER_CLUSTER", float('nan')),
+      # steering wheel buttons; bus assignment is harness dependent
+      ("PCM_BUTTONS", float('nan')),
     ]
 
     cam_messages = [
-      ("ACC_HUD_ADAS", 50),
-      ("MPC_LKAS_CMD", 50),
-      ("ACC_CMD", 25),
+      ("ACC_HUD_ADAS", 10),
+      # stock camera command echoes, only present when stock ADAS is active
+      ("MPC_LKAS_CMD", float('nan')),
+      ("ACC_CMD", float('nan')),
+      # PCM_BUTTONS may be forwarded on the camera bus on some harnesses
+      ("PCM_BUTTONS", float('nan')),
     ]
 
     return {

opendbc_repo/opendbc/sunnypilot/car/byd/mads.py

@@ -19,6 +19,12 @@ class MadsCarState(MadsCarStateBase):
 
   def update_mads(self, ret: structs.CarState, can_parsers: dict[StrEnum, CANParser]) -> None:
     cp = can_parsers[Bus.pt]
+    cp_cam = can_parsers[Bus.cam]
+
+    # PCM_BUTTONS bus assignment is harness dependent; read from whichever bus sees it
+    lkas_button = cp.vl["PCM_BUTTONS"]["LKAS_ON_BTN"]
+    if not cp.vl_all["PCM_BUTTONS"]["LKAS_ON_BTN"] and cp_cam.vl_all["PCM_BUTTONS"]["LKAS_ON_BTN"]:
+      lkas_button = cp_cam.vl["PCM_BUTTONS"]["LKAS_ON_BTN"]
 
     self.prev_lkas_button = self.lkas_button
-    self.lkas_button = cp.vl["PCM_BUTTONS"]["LKAS_ON_BTN"]
+    self.lkas_button = lkas_button