Usage warnings should appear before the long run

A frontend-lab note about placing usage warnings before expensive agent or review runs begin.

The worst place for a usage warning is after the run has already started. For short chat, a small meter in the corner is probably enough. For agent mode, code review, or a repo-wide edit, the warning needs to sit at the launch point: - estimated range - why the range is high - what will happen at the budget limit - one cheaper option I would rather click through one clear pre-run confirmation than discover a vague usage spike in billing later. The placement changes whether the warning feels like control or blame.