feat: ramp-up delay on lat engagement to prevent commIssue flash

Decouples "tell modeld to go fast" from "steering actually active":
- New LatRequested memory param — controlsd writes when lat would be active
- modeld reads LatRequested (not carControl.latActive) for FPS decision,
  so it switches to 20fps immediately on engage request
- controlsd delays CC.latActive becoming true by 250ms (5 frames @ 20fps)
  after LatRequested goes true, giving downstream services
  (longitudinalPlan, liveCalibration, etc.) time to stabilize at the new rate

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

selfdrive/controls/controlsd.py

@@ -172,6 +172,8 @@ class Controls:
     self.not_running_prev = None
     self.last_lat_engage_ts = 0  # CLEARPILOT: timestamp of most recent lat engage transition
     self.prev_lat_active = False
+    self.lat_requested_ts = 0  # CLEARPILOT: timestamp when lat was first requested (for ramp-up delay)
+    self.prev_lat_requested = False
     self.steer_limited = False
     self.desired_curvature = 0.0
     self.experimental_mode = False
@@ -695,8 +697,17 @@ class Controls:
 
     # Check which actuators can be enabled
     standstill = CS.vEgo <= max(self.CP.minSteerSpeed, MIN_LATERAL_CONTROL_SPEED) or CS.standstill
-    CC.latActive = (self.active or self.FPCC.alwaysOnLateral) and self.speed_check and not CS.steerFaultTemporary and not CS.steerFaultPermanent and \
-                   (not standstill or self.joystick_mode)
+    lat_requested = (self.active or self.FPCC.alwaysOnLateral) and self.speed_check and not CS.steerFaultTemporary and not CS.steerFaultPermanent and \
+                    (not standstill or self.joystick_mode)
+
+    # CLEARPILOT: tell modeld early so it can ramp to 20fps, then delay latActive by
+    # 250ms (5 frames at 20fps) so downstream services stabilize before steering engages.
+    self.params_memory.put_bool("LatRequested", lat_requested)
+    now_ts = time.monotonic()
+    if lat_requested and not self.prev_lat_requested:
+      self.lat_requested_ts = now_ts
+    self.prev_lat_requested = lat_requested
+    CC.latActive = lat_requested and (now_ts - self.lat_requested_ts) >= 0.25
     CC.longActive = self.enabled and not self.events.contains(ET.OVERRIDE_LONGITUDINAL) and self.CP.openpilotLongitudinalControl
 
     actuators = CC.actuators