Put token limits on sessions

### Feature summary

Allow users to place token limits on their sessions to prevent overspending

### What problem are you trying to solve?

Long-running agent sessions can easily use up an entire month of AI credits when unsupervised. This would be solved by placing token limits on sessions allowing users to put a cap on the maximum amount of _non-cached_ tokens used.

### Proposed solution

_No response_

### Workflow impact

_No response_

### Installation context

_No response_

### Additional context

_No response_

The issue names no files, tests, or entry points; first locate the session and non-cached token-usage paths. Define how users configure a session cap, when usage is measured, and what happens at the limit. Done means the scope and enforcement behavior are specified and covered by appropriate tests.

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