ABI 2. One body descriptor replaces add_sphere/add_static_box (kinds: sphere, capsule, box, static box).
Revolute, spherical and weld joints created from a world anchor and axis, with joint state lanes (angle,
frame A orientation, relative rotation, relative angular velocity). Per-body force and torque write lanes,
applied before the step then cleared; non-finite values refuse the step. Parent and limb index lanes.
Tests run serially: concurrent b3CreateWorld aborts the host.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
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