Fix wipeout bail teleport NaN physics abort.

Reset biped controller on checkpoint teleport and fall back to identity when skeleton root orthonormalization sees a degenerate axis, preventing poisoned COM frames and deck torque before the shared solve.

Co-authored-by: Cursor <[email protected]>

crates/skate-core/src/physics/skeleton_root.rs

@@ -123,8 +123,16 @@ pub(crate) fn orthonormalize(source: AnimationPartTransform) -> AnimationPartTra
                 *value -= result[prior][lane] * projection;
             }
         }
-        let reciprocal = inverse_length_squared(dot3(vector, vector), 2);
-        result[axis] = vector.map(|v| v * reciprocal);
+        let squared = dot3(vector, vector);
+        if squared <= f32::from_bits(0x3586_37bd) {
+            // Degenerate axes appear after wipeout bail teleports when heading
+            // initialization and ragdoll frames disagree. NaN here poisons COM
+            // frames and deck torque before the shared solve.
+            result[axis] = IDENTITY[axis];
+        } else {
+            let reciprocal = inverse_length_squared(squared, 2);
+            result[axis] = vector.map(|v| v * reciprocal);
+        }
     }
     result
 }
@@ -171,4 +179,16 @@ mod tests {
             }
         }
     }
+
+    #[test]
+    fn degenerate_axis_falls_back_to_identity() {
+        let mut source = IDENTITY;
+        source[0] = [0.; 4];
+        source[1] = [0.; 4];
+        source[2] = [0.; 4];
+        let result = orthonormalize(source);
+        for axis in 0..3 {
+            assert_eq!(result[axis], IDENTITY[axis]);
+        }
+    }
 }

crates/skate-game/src/physics/frame.rs

@@ -86,6 +86,9 @@ pub(super) fn advance(
         super::offboard_root_trace::trace(tick, "teleport", skater);
         //82DB93B0..CC: complete pending queries and clear contact history.
         skater.offboard_contact.reset_history();
+        // Biped cadence survives ordinary Ground reset, but a checkpoint teleport
+        // must not retain an off-board placement from a prior wipeout recovery.
+        skater.biped_ground.controller.reset();
         skater.player_state.reset_for_teleport();
         skater.centre_of_mass_filter.reset();
         skater.animation_feedback.reset();