1. Session completion: column is 'session_date' not 'date'
2. Trainer workload: TrainingGroup has no assignments() — use TrainingSession.trainer_id via employee→user link, count groups via head_trainer_id
3. Wallet balances: Wallet uses polymorphic owner() not participant() — use owner with owner_type filter
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>