Ability to get full conversation history from a session

[domenic]

Right now it's expected that the web developer keep track of previous inputs and outputs themselves; they can only get the "next" output from the model.

However, it might be useful to allow retrieving the full session-so-far from the model. An example API:

const history = await session.history();

// returns an array of { role, content } pairs

This overlaps as a feature request with #50, so if there are independent use cases besides saving to disk or transferring across contexts, please comment with them here.

[domenic]

This could be important for providing better solutions to context window overflow than our built-in strategy of "keep the system prompt, evict in FIFO order otherwise". Exposing the history would then let developers edit it and spawn a new session with the edited history.

However, that approach to editing history might lose some benefits. Consider the case where you want to delete a single message pair from the middle of the conversation. Because you create a whole new session from scratch, the model will likely re-process all the prompts, which is inefficient. If instead we provided some surgical method to remove a specific message pair, I suspect we'd get better efficiency by retaining all the other processed prompts.

(Or maybe, a sufficiently smart cache could keep the efficiency gains, without the need for a surgical method?)