Cap agent steps, time and spend per task

Agents can loop: retrying a failing tool, re-reading the same document, or calling each other. Unbounded consumption is on the OWASP list for a reason.

Set a limit on every dimension a task can grow along:

• a maximum number of model calls and tool calls per task;
• a wall-clock timeout;
• a token or cost budget.

When any one is hit, stop cleanly with a useful message and record which limit stopped the task.