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.

Written by the indexing model from the issue text.