Body step 2.2: fix the 2.1 headset instabilities

Spike now runs real input (90 Hz sample-and-hold tracking + jitter under 144 Hz
physics), which reproduced the playtest. Root causes fixed:
- PoseFilter/RagdollDriver: timestamped extrapolation of tracking, one tick
  pipeline shared by PlayerRig and the spike
- low-pass all feed-forwards (ground control amplified jitter by body mass)
- arm muscles back to local targets (physical-frame aim fed chest rotation back)
- structural hand strength only when braced or holding
- no free-path view chasing while grounded (8 m crouch slide); stick hold-back
- explicit inertia for the Legs body (shape-less tuck tumbled the pelvis)
- world grab: Box3D shape queries return a null collider, use collider_id
- new crouch-hold phases; world-grab detection asserted

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

scripts/PropGrabber.cs

@@ -11,7 +11,7 @@ public partial class PropGrabber : Node
     private const float BreakTime = 0.25f;
     private const float BreakDistanceBoth = 0.4f;
     private const float GripRipDistance = 0.8f;
-    private const float WorldGrabRadius = 0.05f;   // palm sphere for grabbing static world (ledges, bars, holds)
+    private const float WorldGrabRadius = 0.07f;   // palm sphere for grabbing static world (ledges, bars, holds)
     public const string NoGrabGroup = "no_grab";   // static bodies that can't be grabbed (the floor)
 
     private static PropGrabber _instance;
@@ -197,7 +197,7 @@ public partial class PropGrabber : Node
         _breakTimer[hand] = 0f;
     }
 
-    private static Vector3 PalmPoint(RigidBody3D handBody, int hand) =>
+    public static Vector3 PalmPoint(RigidBody3D handBody, int hand) =>
         handBody.GlobalPosition + handBody.GlobalTransform.Basis * new Vector3(PalmOffset(hand), 0f, 0f);
 
     private static float PalmOffset(int hand) => hand == 0 ? PalmGrabOffset : -PalmGrabOffset;
@@ -214,11 +214,12 @@ public partial class PropGrabber : Node
         nearest = NearestProp(handBody.GlobalPosition, CenterGrabRadius);
         if (nearest != null)
             return nearest;
-        return WorldUnderPalm(palm, handBody.GetWorld3D());
+        return WorldUnderPalm(palm, handBody.GetWorld3D()) ?? WorldUnderPalm(handBody.GlobalPosition, handBody.GetWorld3D());
     }
 
-    // Climbing: any static body touching the palm (except the "no_grab" group) can be held.
-    private static StaticBody3D WorldUnderPalm(Vector3 palm, World3D world)
+    // Climbing: any static body near the palm (except the "no_grab" group) can be held.
+    // NOTE (Box3D wrapper): shape-query results carry a null "collider" — resolve "collider_id".
+    public static StaticBody3D WorldUnderPalm(Vector3 palm, World3D world)
     {
         PhysicsShapeQueryParameters3D query = new()
         {
@@ -228,7 +229,7 @@ public partial class PropGrabber : Node
         };
         foreach (Godot.Collections.Dictionary hit in world.DirectSpaceState.IntersectShape(query, 8))
         {
-            if (hit["collider"].AsGodotObject() is StaticBody3D body && !body.IsInGroup(NoGrabGroup))
+            if (GodotObject.InstanceFromId((ulong)hit["collider_id"]) is StaticBody3D body && !body.IsInGroup(NoGrabGroup))
                 return body;
         }
         return null;