Lodur.Core: engine-free PD law with per-muscle strength. Lodur.Body.Ymir: 13-body, 12-joint ragdoll
driven through the world's torque lanes from caller-owned strength and target arrays. Tests: stand, fall,
rest, per-muscle strength, torque conservation, no allocation, same seed gives the same state hash.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>