Elbow: read the hand-suggested angle nearest the current one (fixes side-switching when pointing the controller down: 45 -> 0 switches); point-down spike phase

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

scripts/ArmSpike.cs

@@ -53,6 +53,8 @@ public partial class ArmSpike : Node3D
     private float _maxElbowStep;
     private Vector3 _lastElbow;
     private float _maxPinHandLag;
+    private float _downSide;
+    private int _downSideSwitches;
     private float _restBodyPen;
     private float _restDrawnPen;
     private float _restAnvilMove;
@@ -178,13 +180,31 @@ public partial class ArmSpike : Node3D
                 Vector3 axis = (handPos - _arms.Shoulder(1)).Normalized();
                 Vector3 perp = axis.Cross(Vector3.Up).Normalized();
                 Vector3 fwd = (axis * Mathf.Cos(1.22f) + perp.Rotated(axis, Mathf.Tau * _phaseT) * Mathf.Sin(1.22f)).Normalized();
-                _handTarget[1] = new Transform3D(Basis.LookingAt(fwd, Mathf.Abs(fwd.Y) > 0.95f ? Vector3.Forward : Vector3.Up), handPos);
+                if (_phaseT <= 3.5f)
+                    _handTarget[1] = new Transform3D(Basis.LookingAt(fwd, Mathf.Abs(fwd.Y) > 0.95f ? Vector3.Forward : Vector3.Up), handPos);
                 Vector3 elbow = _arms.ElbowTarget(1);
                 if (_phaseT > 0.5f)
                     _maxElbowStep = Mathf.Max(_maxElbowStep, elbow.DistanceTo(_lastElbow));
                 _lastElbow = elbow;
-                if (_phaseT > 3.5f)
+                if (_phaseT > 3.5f && _phaseT <= 5.5f)
                 {
+                    // Controller pointing straight down with tracker-like wobble: the elbow
+                    // must stay on one side.
+                    Vector3 wobble = new Vector3(Mathf.Sin(5f * _phaseT), 0f, Mathf.Cos(3.7f * _phaseT)) * 0.5f;
+                    Vector3 down = (Vector3.Down + wobble).Normalized();
+                    _handTarget[1] = new Transform3D(Basis.LookingAt(down, Vector3.Forward), handPos);
+                    float sideNow = Mathf.Sign((_arms.ElbowTarget(1) - _arms.Shoulder(1)).Dot(_torso.Body.GlobalTransform.Basis.X));
+                    if (_phaseT > 4f)
+                    {
+                        if (_downSide == 0f)
+                            _downSide = sideNow;
+                        else if (sideNow != _downSide)
+                            _downSideSwitches++;
+                    }
+                }
+                if (_phaseT > 5.5f)
+                {
+                    Record($"point-down: elbow keeps its side under wobble (switches {_downSideSwitches})", _downSideSwitches == 0);
                     Record($"flip: elbow never jumps (max step {_maxElbowStep:F4} m/tick, limit {FlipElbowStepLimit})", _maxElbowStep < FlipElbowStepLimit);
                     _handTarget[1] = new Transform3D(Basis.Identity, _handRest[1]);
                     _maxHoldPenetration = 0f;

scripts/PhysicsArms.cs

@@ -331,7 +331,14 @@ public partial class PhysicsArms : Node
             handElbow -= dir * handElbow.Dot(dir);
             float confidence = Mathf.Clamp(handElbow.Length() / (0.5f * radius + 1e-4f), 0f, 1f);
             if (handElbow.LengthSquared() > 1e-8f)
-                targetAngle = Mathf.Atan2(handElbow.Dot(refB), handElbow.Dot(refN)) * PoleHandWeight * confidence;
+            {
+                // Read the suggestion as the representation NEAREST the current elbow angle:
+                // pointing the controller down puts it at the ±180° seam, where jitter would
+                // otherwise flip the clamped elbow to the other side.
+                float raw = Mathf.Atan2(handElbow.Dot(refB), handElbow.Dot(refN));
+                raw = _poleAngle[index] + Mathf.Wrap(raw - _poleAngle[index], -Mathf.Pi, Mathf.Pi);
+                targetAngle = raw * PoleHandWeight * confidence;
+            }
         }
         targetAngle = Mathf.Clamp(targetAngle, -PoleMaxAngle, PoleMaxAngle);
         float step = (targetAngle - _poleAngle[index]) * (1f - Mathf.Exp(-delta * PoleSmoothRate));