fixed: Implement urgency-based rate limiting for longitudinal control

Modified the acceleration and deceleration smoothing logic in longcontrol.py to dynamically adjust the rate of acceleration change based on deceleration urgency. This enhances responsiveness during urgent braking scenarios while maintaining smooth acceleration.

Generated by Copilot

(cherry picked from commit f6cbb584a3420b2f27af3c911106f34f43aa3549)
(cherry picked from commit ccf722452e61bb62869d2d6885c0679d9ffa2c8f)

selfdrive/controls/lib/longcontrol.py

@@ -179,6 +179,26 @@ class LongControl:
       else:
         output_accel = raw_output_accel
 
+    if self.long_control_state == LongCtrlState.pid:
+      # Smooth acceleration and deceleration with urgency-based rate limiting
+      base_rate = 1.0
+      
+      if output_accel < self.last_output_accel:  # Deceleration requested
+          decel_needed = self.last_output_accel - output_accel
+          # Use a safe default for ACCEL_MIN if not available, to prevent division by zero
+          max_decel = abs(CarControllerParams.ACCEL_MIN) if CarControllerParams.ACCEL_MIN != 0 else 4.0
+          urgency = min(1.0, decel_needed / max_decel)
+          
+          # Adjust rate based on urgency (1.0 m/s^3 for low urgency, up to 4.0 m/s^3 for high urgency)
+          max_rate = 1.0 + 3.0 * urgency
+      else:
+          max_rate = base_rate  # Acceleration is always smooth
+      
+      max_accel_change = max_rate * DT_CTRL
+      output_accel = clip(output_accel,
+                          self.last_output_accel - max_accel_change,
+                          self.last_output_accel + max_accel_change)
+
     self.last_output_accel = clip(output_accel, accel_limits[0], accel_limits[1])
     return self.last_output_accel