[Feature Request] Separate cached token tracking for brainstorming sessions from main session

Question

**Bug Description**
It would be good to have brainstorming (user intiated from the main session) as a seperate cached token detached from the main session uncached count. This would avoid a large uncached token running on the main session when we start to work on a feature (which at the start might be like a quick session) but might grow into a big session with lots of uncached token and we have write expcitly to a plan file before clearing context and start from the plan file again.

**Environm