Body step 2: the player is a muscle-driven ragdoll (Project TX)

PlayerRagdoll: 9 bodies, spine/neck ball joints, shoulder drives (girdle + muscle),
elbow hinges, torque-capped motor PDs toward the True Body, chest->hand guides,
implicit balance motor, mass-scaled ground control. PlayerRig: XR driver with
stick move / snap turn and Bonelab-style push-back (eye->camera sphere sweep).
Replaces the chase bodies in main.tscn; RagdollSpike regression (14 phases).

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

scripts/ArmSolver.cs

@@ -20,6 +20,9 @@ public sealed class ArmSolver
 
     public Vector3 Elbow { get; private set; }
     public Vector3 Wrist { get; private set; }
+    // Unit vector from the arm axis toward the elbow (defined even for a straight arm); the
+    // elbow hinge axis is Pole × (shoulder→wrist).
+    public Vector3 Pole { get; private set; } = Vector3.Back;
 
     // side = the arm's outward direction (−torso X for the left arm, +X for the right).
     // handBasis = the controller's basis (null → torso-frame reference only).
@@ -78,7 +81,8 @@ public sealed class ArmSolver
         _poleAngle += Mathf.Clamp(step, -PoleMaxSpeed * delta, PoleMaxSpeed * delta);
         Vector3 pole = refN.Rotated(dir, _poleAngle);
 
-        Elbow = center + CapElbowHeight(pole, dir, center, radius, Mathf.Max(shoulder.Y, wrist.Y) + ElbowRiseAllowance) * radius;
+        Pole = CapElbowHeight(pole, dir, center, radius, Mathf.Max(shoulder.Y, wrist.Y) + ElbowRiseAllowance);
+        Elbow = center + Pole * radius;
         Wrist = Elbow + (wrist - Elbow).Normalized() * foreLen;
     }