Accumulated pricing after model changes does not persist across session reload

[katzdave]

Describe the bug

There is some client side code to handle this but if I were to use:

cheap model

• talk to goose a bunch expensive model
• talk to goose a bunch

reload session

It has no recollection of what was part of cheap vs expensive model.

I think my ideal fix would be to attach some metadata to the session around what provider/model a session started with and when.switches occur. Something simpler could be to just store the accumulated cost, not just the accumulated tokens.