train-w2z55 rewound to epoch 0 (improvement_rate=17.3, val_Sharpe=17.3)
instead of epoch 20 (improvement_rate=0.4, val_Sharpe=45.4). The model
lost ALL learned behavior and couldn't re-learn at low cosine LR.
Fix: sort checkpoints by val_Sharpe (highest first). Rewind targets the
BEST state (val_Sharpe=45), not the fastest-climbing moment (epoch 0).
Added val_sharpe field to TrajectoryCheckpoint for proper ranking.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>