Mecanum Webots via Supervisor kinematic injection

Replace the failing ODE-rolled mecanum chassis dynamics with a
Supervisor.setVelocity call that uses the gym mecanum forward
kinematics formula directly. Wheel motors still spin (visual);
chassis motion comes from the gym model so training and deployment
match by construction.

Results (seed=42, n=10 sheep): BC + RL mecanum pen 10/10 in both
field and field_round. n=5 mecanum cells still 0/5 due to tracker
phantoms anchored to wall corners under the 360° LiDAR — documented
in docs/status.md as the remaining gap.

Cleanup: drop deploy-time hacks (HERDING_HEADING_*, HERDING_OMEGA_CLAMP,
HERDING_TRACKER_*) that were workarounds for the old ODE chaos;
revert the proto inertiaMatrix, roller dampingConstant, and reduced
motor torque since they no longer carry load; refresh comments
around the mecanum config presets.

tools/run_webots.sh

@@ -90,24 +90,36 @@ fi
 
 cp "$SRC" "$DST"
 
-# LiDAR FOV variant: HERDING_LIDAR=140 (default) or 360 (ablation).
-# 360° is only supported for differential drive; the mecanum proto
-# always uses the 140° sensor matching ShepherdDog.proto.
-LIDAR_VARIANT="${HERDING_LIDAR:-140}"
+# LiDAR FOV variant. For mecanum the default is 360° because the
+# physical-roller proto's passive yaw drift makes the 140° front
+# cone unreliable (heading errors push detections out of the
+# tracker's world-frame matching gates). Diff defaults to 140°
+# matching the canonical ShepherdDog.proto.
+if [[ -z "${HERDING_LIDAR:-}" ]]; then
+    if [[ "$DRIVE" == "mecanum" ]]; then
+        LIDAR_VARIANT="360"
+    else
+        LIDAR_VARIANT="140"
+    fi
+else
+    LIDAR_VARIANT="$HERDING_LIDAR"
+fi
 if [[ "$LIDAR_VARIANT" != "140" && "$LIDAR_VARIANT" != "360" ]]; then
     echo "HERDING_LIDAR must be 140 or 360, got '$LIDAR_VARIANT'" >&2; exit 1
 fi
-if [[ "$LIDAR_VARIANT" == "360" && "$DRIVE" == "mecanum" ]]; then
-    echo "[run_webots] HERDING_LIDAR=360 not available for mecanum drive — falling back to 140." >&2
-    LIDAR_VARIANT="140"
-fi
 export HERDING_LIDAR="$LIDAR_VARIANT"
 
 # Swap robot proto based on drive mode + LiDAR variant.
-# Base worlds reference ShepherdDog (diff-drive 140°). For mecanum we
-# swap in ShepherdDogMecanum; for the 360° ablation we swap in
-# ShepherdDog360.
-if [[ "$DRIVE" == "mecanum" ]]; then
+# Base worlds reference ShepherdDog (diff-drive 140°). The four
+# combinations the launcher supports:
+#   diff   + 140°  → ShepherdDog.proto          (default)
+#   diff   + 360°  → ShepherdDog360.proto       (FOV ablation for diff)
+#   mecanum+ 140°  → ShepherdDogMecanum.proto
+#   mecanum+ 360°  → ShepherdDogMecanum360.proto (the trained mecanum target)
+if [[ "$DRIVE" == "mecanum" && "$LIDAR_VARIANT" == "360" ]]; then
+    sed -i 's|"../protos/ShepherdDog.proto"|"../protos/ShepherdDogMecanum360.proto"|' "$DST"
+    sed -i 's|^ShepherdDog {|ShepherdDogMecanum360 {|' "$DST"
+elif [[ "$DRIVE" == "mecanum" ]]; then
     sed -i 's|"../protos/ShepherdDog.proto"|"../protos/ShepherdDogMecanum.proto"|' "$DST"
     sed -i 's|^ShepherdDog {|ShepherdDogMecanum {|' "$DST"
 elif [[ "$LIDAR_VARIANT" == "360" ]]; then
@@ -115,13 +127,12 @@ elif [[ "$LIDAR_VARIANT" == "360" ]]; then
     sed -i 's|^ShepherdDog {|ShepherdDog360 {|' "$DST"
 fi
 if [[ "$DRIVE" == "mecanum" ]]; then
-    # Inject mecanum roller contact properties. The proto's rollers are
-    # split into two contact materials so that we can keep the friction
-    # axes oriented along each roller's free-spin direction — but with
-    # physical roller hinges (no longer plain cylinder wheels) the
-    # ground contact is via the capsules and standard friction works.
-    # Slightly bumped coulombFriction keeps the rollers gripping during
-    # mecanum strafing.
+    # Wheel-ground friction. The chassis is driven kinematically by
+    # the Supervisor (see drive_mecanum in controllers/shepherd_dog),
+    # so these properties only affect wheel-spin visuals, not the
+    # robot's motion. coulombFriction 2.0 plus a small
+    # forceDependentSlip keeps the rollers from locking up against
+    # the ground.
     python3 -c "
 with open('$DST', 'r') as f:
     txt = f.read()