nx_skill_coach_dance.nx

nx_skill_coach_dance.nx -- SKILL-COACH vision/DANCE vertical, the COACH LOOP (parallel to audio R1). Given pose KEYPOINTS (joint x,y), compute JOINT ANGLES, grade vs a reference pose, diagnose WHICH joint is off (too bent / too straight) -> drill. This is the dance-coach core; the PERCEPTION (camera->keypoints = a sovereign bits-up pose-net) is the RESEARCHER-owned research arc CAP-COACH-POSE -- here keypoints are synthetic (the pose-net is the separate long-pole, exactly as nx_pitch was the separate perception for audio R1). Pure integer (cos via dot/|.|, isqrt; NO floats, NO acos -- compare cosines: larger cos = smaller angle = more bent). license_tier: ORIGINAL