Give cross-body bars a true 3D axis and fix the goblet squat hold

The orbit was always a real camera orbit — figure and props share one
rigid rotation — but a bar's screen-space angle authored the wrong 3D
rod: the default horizontal encoded a rod along the body axis, so
barbells hovered fixed on screen and vanished at the head-on view
where they should span widest. Line props now take "axis": "z" (both
renderers in lockstep, fixture-pinned): the world left-right direction
projects through the camera pitch like the floor quad — end-on plates
in profile, full span face-on, swinging with the hands in between.
Applied to the ten cross-body bars; vertical handles were already
orbit-invariant.

Goblet Squat's hand pins sat so close to the shoulders that the
two-bone IK was degenerate, flipping between a chicken-wing and an
elbow-behind solve; re-pinned level with the shoulders so the elbows
tuck straight down through the whole rep.

Claude-Session: https://claude.ai/code/session_01HJDQQDA9QdP8zByg43H5v3

Workouts/ExerciseFigure/ExerciseMotion.swift

@@ -178,6 +178,10 @@ struct MotionProp: Codable {
     /// Fixed world angle (degrees, y-up). Default: bars are horizontal;
     /// dumbbells/pads sit perpendicular to the lower bone.
     let angle: Double?
+    /// True 3D axis, superseding `angle`: `"z"` marks a cross-body rod
+    /// (barbell, pull-up bar) whose projection foreshortens naturally —
+    /// end-on in a profile view, full span face-on.
+    let axis: String?
     let halfLen: Double?
     let w: Double?
     /// End-disc radius (dumbbell plates default 4.5; bars none).

Workouts/ExerciseFigure/MotionSolver.swift

@@ -576,10 +576,13 @@ enum MotionSolver {
     /// `anchor` the frame's root canvas anchor, and `rotation` the `propRotation`
     /// between them. Joint positions come from `geo`; everything authored — scene
     /// points, cable anchors, bar angles, pad perpendiculars, roller offsets —
-    /// resolves against `authored` and rotates. Kept 1:1 with the reference
-    /// renderer's `resolve_props` — change them in lockstep.
+    /// resolves against `authored` and rotates. `pitch` is the camera elevation,
+    /// needed by `axis` props whose world-space direction projects through it
+    /// (like the floor quad). Kept 1:1 with the reference renderer's
+    /// `resolve_props` — change them in lockstep.
     static func resolveProps(_ props: [MotionProp], geo: FigureGeometry, authored: FigureGeometry,
-                             anchor: CGPoint, rotation: Mat3?) -> (bg: [PropPrimitive], fg: [PropPrimitive]) {
+                             anchor: CGPoint, rotation: Mat3?,
+                             pitch: Double = MotionSolver.defaultPitch) -> (bg: [PropPrimitive], fg: [PropPrimitive]) {
         /// Authored canvas point (+ depth toward the camera) → drawn canvas.
         func place(_ x: Double, _ y: Double, _ z: Double) -> CGPoint {
             guard let rotation else { return CGPoint(x: x, y: y) }
@@ -654,13 +657,23 @@ enum MotionSolver {
                 }
                 guard let at = prop.at, let now = jointAnchor(geo, at),
                       let auth = jointAnchor(authored, at) else { continue }
-                let axis: CGVector
-                if prop.type == "bar" || prop.angle != nil {
-                    axis = direction(prop.angle ?? 0)          // fixed authored-view angle
+                let u: CGVector
+                if prop.axis == "z" {
+                    // A cross-body rod (barbell, pull-up bar): its true 3D axis
+                    // is the world left-right axis, projected through the camera
+                    // elevation like the floor quad — a small vertical sliver
+                    // end-on in a profile view (the plates read nearly
+                    // concentric, seen from slightly above), full span face-on,
+                    // swinging with the figure in between, symmetric at 0 and 180.
+                    let pr = pitch * .pi / 180
+                    let axis = Vec3(0, -sin(pr), cos(pr))
+                    let v = rotation?.apply(axis) ?? axis
+                    u = CGVector(dx: v.x, dy: -v.y)
+                } else if prop.type == "bar" || prop.angle != nil {
+                    u = swing(direction(prop.angle ?? 0))      // fixed authored-view angle, foreshortens under orbit
                 } else {
-                    axis = CGVector(dx: -auth.direction.dy, dy: auth.direction.dx)
+                    u = swing(CGVector(dx: -auth.direction.dy, dy: auth.direction.dx))
                 }
-                let u = swing(axis)                            // foreshortens under orbit
                 let h = prop.halfLen ?? defaults.halfLen
                 let a = CGPoint(x: now.point.x - u.dx * h, y: now.point.y - u.dy * h)
                 let b = CGPoint(x: now.point.x + u.dx * h, y: now.point.y + u.dy * h)
@@ -764,7 +777,8 @@ struct MotionTimeline {
         guard !props.isEmpty else { return geo }
         let rotation = MotionSolver.propRotation(pitch: pitch, yawOffset: yawOffset)
         (geo.propsBackground, geo.propsForeground) = MotionSolver.resolveProps(
-            props, geo: geo, authored: authored, anchor: frame.rootPos, rotation: rotation)
+            props, geo: geo, authored: authored, anchor: frame.rootPos, rotation: rotation,
+            pitch: pitch)
         return geo
     }
 }

Workouts/Resources/ExerciseMotions/Barbell Squat.motion.json

@@ -4,7 +4,7 @@
   "camera": {"zoom": 0.7},
   "working": ["leg_r", "leg_l"],
   "props": [
-    {"type": "bar", "at": ["hand_r", "hand_l"], "halfLen": 26, "plateR": 14}
+    {"type": "bar", "axis": "z", "at": ["hand_r", "hand_l"], "halfLen": 26, "plateR": 14}
   ],
   "frames": [
     {

Workouts/Resources/ExerciseMotions/Bench Press.motion.json

@@ -8,7 +8,7 @@
       {"kind": "line", "pts": [[78, 129], [78, 150]], "w": 4},
       {"kind": "line", "pts": [[144, 129], [144, 150]], "w": 4}
     ]},
-    {"type": "bar", "at": ["hand_r", "hand_l"], "halfLen": 26, "plateR": 12}
+    {"type": "bar", "axis": "z", "at": ["hand_r", "hand_l"], "halfLen": 26, "plateR": 12}
   ],
   "frames": [
     {

Workouts/Resources/ExerciseMotions/Deadlift.motion.json

@@ -4,7 +4,7 @@
   "camera": {"zoom": 0.7},
   "working": ["leg_r", "leg_l", "spine"],
   "props": [
-    {"type": "bar", "at": ["hand_r", "hand_l"], "halfLen": 26, "plateR": 16}
+    {"type": "bar", "axis": "z", "at": ["hand_r", "hand_l"], "halfLen": 26, "plateR": 16}
   ],
   "frames": [
     {

Workouts/Resources/ExerciseMotions/Goblet Squat.motion.json

@@ -12,24 +12,24 @@
       "root": {"pos": [160, 66], "pitch": 5},
       "spine": [0, 0],
       "neck": 2, "head": -6,
-      "shoulder_r": 38, "elbow_r": 125,
-      "shoulder_l": 38, "elbow_l": 125,
+      "shoulder_r": 5, "elbow_r": 140,
+      "shoulder_l": 5, "elbow_l": 140,
       "hip_r": 5, "knee_r": 4, "ankle_r": 0,
       "hip_l": 5, "knee_l": 4, "ankle_l": 0,
       "pins": {"foot_r": [162, 148], "foot_l": [166, 150],
-               "hand_r": [176, -2], "hand_l": [180, 0]}
+               "hand_r": [185, -8], "hand_l": [189, -6]}
     },
     {
       "hold": 0.4, "tween": 1.0,
       "root": {"pos": [150, 104], "pitch": 22},
       "spine": [0, -4],
       "neck": 4, "head": -18,
-      "shoulder_r": 46, "elbow_r": 120,
-      "shoulder_l": 46, "elbow_l": 120,
+      "shoulder_r": 15, "elbow_r": 135,
+      "shoulder_l": 15, "elbow_l": 135,
       "hip_r": 96, "knee_r": 116, "ankle_r": 20,
       "hip_l": 96, "knee_l": 116, "ankle_l": 20,
       "pins": {"foot_r": [162, 148], "foot_l": [166, 150],
-               "hand_r": [190, 40], "hand_l": [194, 42]}
+               "hand_r": [196, 36], "hand_l": [200, 38]}
     }
   ]
 }

Workouts/Resources/ExerciseMotions/Hip Thrust.motion.json

@@ -7,7 +7,7 @@
       {"kind": "line", "pts": [[50, 122], [88, 122]], "w": 9, "depth": 8},
       {"kind": "line", "pts": [[68, 127], [68, 150]], "w": 5}
     ]},
-    {"type": "bar", "at": ["hand_r", "hand_l"], "halfLen": 26, "plateR": 13}
+    {"type": "bar", "axis": "z", "at": ["hand_r", "hand_l"], "halfLen": 26, "plateR": 13}
   ],
   "frames": [
     {

Workouts/Resources/ExerciseMotions/Incline Bench Press.motion.json

@@ -9,7 +9,7 @@
       {"kind": "line", "pts": [[140, 130], [166, 127]], "w": 8, "depth": 8},
       {"kind": "line", "pts": [[152, 133], [152, 150]], "w": 5}
     ]},
-    {"type": "bar", "at": ["hand_r", "hand_l"], "halfLen": 26, "plateR": 12}
+    {"type": "bar", "axis": "z", "at": ["hand_r", "hand_l"], "halfLen": 26, "plateR": 12}
   ],
   "frames": [
     {

Workouts/Resources/ExerciseMotions/Lat Pull Down.motion.json

@@ -9,7 +9,7 @@
       {"kind": "circle", "c": [272, 19], "r": 4, "fill": true, "color": "prop"}
     ]},
     {"type": "cable", "from": [272, 19], "to": ["hand_r", "hand_l"], "w": 4},
-    {"type": "bar", "at": ["hand_r", "hand_l"], "halfLen": 24}
+    {"type": "bar", "axis": "z", "at": ["hand_r", "hand_l"], "halfLen": 24}
   ],
   "frames": [
     {

Workouts/Resources/ExerciseMotions/Pull-Up.motion.json

@@ -4,7 +4,7 @@
   "camera": {"zoom": 0.7},
   "working": ["arm_r", "arm_l"],
   "props": [
-    {"type": "bar", "at": ["hand_r", "hand_l"], "halfLen": 24}
+    {"type": "bar", "axis": "z", "at": ["hand_r", "hand_l"], "halfLen": 24}
   ],
   "frames": [
     {

Workouts/Resources/ExerciseMotions/Romanian Deadlift.motion.json

@@ -4,7 +4,7 @@
   "camera": {"zoom": 0.7},
   "working": ["leg_r", "leg_l", "spine"],
   "props": [
-    {"type": "bar", "at": ["hand_r", "hand_l"], "halfLen": 26, "plateR": 13}
+    {"type": "bar", "axis": "z", "at": ["hand_r", "hand_l"], "halfLen": 26, "plateR": 13}
   ],
   "frames": [
     {

Workouts/Resources/ExerciseMotions/Shoulder Press.motion.json

@@ -9,7 +9,7 @@
       {"kind": "line", "pts": [[126, 143], [126, 151]], "w": 5},
       {"kind": "line", "pts": [[110, 151], [142, 151]], "w": 4, "depth": 5}
     ]},
-    {"type": "bar", "at": ["hand_r", "hand_l"], "halfLen": 10}
+    {"type": "bar", "axis": "z", "at": ["hand_r", "hand_l"], "halfLen": 10}
   ],
   "frames": [
     {

Workouts/Resources/ExerciseMotions/Triceps Pushdown.motion.json

@@ -8,7 +8,7 @@
       {"kind": "circle", "c": [186, -58], "r": 4, "fill": true, "color": "prop"}
     ]},
     {"type": "cable", "from": [186, -58], "to": ["hand_r", "hand_l"], "w": 3},
-    {"type": "bar", "at": ["hand_r", "hand_l"], "halfLen": 10}
+    {"type": "bar", "axis": "z", "at": ["hand_r", "hand_l"], "halfLen": 10}
   ],
   "frames": [
     {