bot: fix slow/unsteerable driving + controls tooltip

Diagnosis (agent + live values): tuning & tread geometry were fine, debugAutoDrive
off — the real drag was the box chassis sliding on default ~0.6 friction, which ate
forward speed AND resisted yaw (dead steering).
- Bot_LowFriction physics material (0.3, Minimum combine) on the chassis → slides +
  yaws freely.
- TreadPart yaw-assist (220 N·m, sign reinforces natural differential) so a throttle
  difference gives a clear turn; cancels to zero on equal throttle (straight kept).
- SeatManager: context-aware controls tooltip under the seat box (on-foot vs driving),
  with a 'turn: differ vs teammate' hint.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Assets/Physics/Bot_LowFriction.physicsMaterial

@@ -0,0 +1,15 @@
+%YAML 1.1
+%TAG !u! tag:unity3d.com,2011:
+--- !u!134 &13400000
+PhysicsMaterial:
+  m_ObjectHideFlags: 0
+  m_CorrespondingSourceObject: {fileID: 0}
+  m_PrefabInstance: {fileID: 0}
+  m_PrefabAsset: {fileID: 0}
+  m_Name: Bot_LowFriction
+  serializedVersion: 2
+  m_DynamicFriction: 0.3
+  m_StaticFriction: 0.3
+  m_Bounciness: 0
+  m_FrictionCombine: 2
+  m_BounceCombine: 2

Assets/Physics/Bot_LowFriction.physicsMaterial.meta

@@ -0,0 +1,7 @@
+fileFormatVersion: 2
+guid: 6c687d24b6f5fbb4783d28d635f71a29
+DefaultImporter:
+  externalObjects: {}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

Assets/Scenes/M1_Arena.unity

@@ -1639,12 +1639,18 @@ MonoBehaviour:
   m_Script: {fileID: 11500000, guid: cd21368c9a8b1064d913c375fb607c0b, type: 3}
   m_Name: 
   m_EditorClassIdentifier: Assembly-CSharp::Jankenbots.Prototype.CameraDirector
-  avatarOffset: {x: 0, y: 4, z: -6}
+  avatarDistance: 8
-  robotOffset: {x: 0, y: 8, z: -12}
+  robotDistance: 16
+  lookSensitivity: 0.18
+  zoomSensitivity: 4
+  minDistance: 3
+  maxDistance: 80
+  minPitch: -8
+  maxPitch: 78
+  lookHeight: 1.2
   orbitRadius: 20
   orbitHeight: 9
   orbitSpeed: 18
-  lookHeight: 1.2
 --- !u!1001 &579422633
 PrefabInstance:
   m_ObjectHideFlags: 0
@@ -3441,7 +3447,7 @@ BoxCollider:
   m_PrefabInstance: {fileID: 0}
   m_PrefabAsset: {fileID: 0}
   m_GameObject: {fileID: 781174154}
-  m_Material: {fileID: 0}
+  m_Material: {fileID: 13400000, guid: 6c687d24b6f5fbb4783d28d635f71a29, type: 2}
   m_IncludeLayers:
     serializedVersion: 2
     m_Bits: 0
@@ -5564,6 +5570,7 @@ MonoBehaviour:
   chassis: {fileID: 0}
   cruiseForce: 450
   throttleDeadzone: 0.08
+  yawAssistTorque: 220
   pivotAnchorStrength: 1500
   pivotAngularResistance: 400
   leanTorque: 500
@@ -5699,6 +5706,7 @@ MonoBehaviour:
   chassis: {fileID: 0}
   cruiseForce: 450
   throttleDeadzone: 0.08
+  yawAssistTorque: 220
   pivotAnchorStrength: 1500
   pivotAngularResistance: 400
   leanTorque: 500

Assets/Scripts/Bot/SeatManager.cs

@@ -179,6 +179,20 @@ namespace Jankenbots.Prototype
             {
                 ReleaseSeatRpc();
             }
+
+            // Controls hint under the seat box — context-aware (on foot vs driving).
+            int ty = y + h + 6, th = 54;
+            GUI.Box(new Rect(x, ty, w, th), "Controls");
+            if (mine.HasValue)
+            {
+                GUI.Label(new Rect(x + 10, ty + 20, w - 20, 18), "W throttle · LShift pivot · A/D lean");
+                GUI.Label(new Rect(x + 10, ty + 34, w - 20, 18), "Q leave · V camera · turn: differ vs teammate");
+            }
+            else
+            {
+                GUI.Label(new Rect(x + 10, ty + 20, w - 20, 18), "WASD move · Mouse look · Scroll zoom");
+                GUI.Label(new Rect(x + 10, ty + 34, w - 20, 18), "E claim tread · V camera · Esc free cursor");
+            }
         }
 
         static string SeatLabel(ulong pilot) => pilot == NoPilot ? "free" : $"#{pilot}";

Assets/Scripts/Bot/TreadPart.cs

@@ -63,6 +63,9 @@ namespace Jankenbots.Prototype
         [Range(0f, 0.5f)]
         public float throttleDeadzone = 0.08f;
 
+        [Tooltip("Extra yaw torque (N·m) at full throttle, REINFORCING the natural differential turn so steering reads clearly even with ground friction. Left/Right push opposite ways, so equal throttle cancels to zero → straight line preserved. Set 0 to rely on pure emergent differential. Flip sign in code if it ever fights the turn.")]
+        public float yawAssistTorque = 220f;
+
         // ---- (b) LOCK-PIVOT tuning -----------------------------------------------
         [Header("(b) Lock-pivot — plant this tread as an anchor")]
         [Tooltip("How hard the planted tread resists the chassis sliding at its position.")]
@@ -192,6 +195,13 @@ namespace Jankenbots.Prototype
             {
                 Vector3 drive = transform.forward * (_throttle * cruiseForce);
                 chassis.AddForceAtPosition(drive, treadPos, ForceMode.Force);
+
+                // Yaw assist: reinforce the differential turn (Left throttles → nose right,
+                // Right throttles → nose left). Cancels to zero when both throttle equally,
+                // so straight-line driving is untouched; the maxAngularVelocity clamp still
+                // caps total spin so this can't reintroduce an uncontrolled tip.
+                float yawSign = side == Side.Left ? 1f : -1f;
+                chassis.AddTorque(chassis.transform.up * (yawSign * _throttle * yawAssistTorque), ForceMode.Force);
             }
 
             // ---- (c) PASSIVE LEAN — anti-tip ballast ---------------------------