A coding agent re-sends its whole conversation every turn, so the frightening line item is input tokens — except that 98.6% of them were served from the provider’s prefix cache, which makes a flat input price overstate the real bill about sevenfold. Fit cost against what actually varies across 600 trajectories and turn count explains 84% of it; the average size of what the tools printed back explains 4%. The lever is the loop, not the logs.