add `experimental_context` parameter to `prepareStep` callback

[rogercbe]

Description

Any change to reconsider this PR?
#10171

It was closed in favour of this (#9682) however I think that it is not really an alternative since the options cannot be changed (as far as I know) in the tools execution and, options are not available (yet?) on the prepareStep either.

I think it would be very convenient to have the context available on the prepareStep arguments. In our use case, we have a tool that delegates/handoffs to an agent and setting the agentId on the context and the prepareStep would retrieve the necesary tools for that agent and set the system/activeTools for the specific agent.

Can we reconsider this? Or is there a recommended alternative to achieve this?

AI SDK Version

• "ai": "6.0.0-beta.105",

Code of Conduct

• I agree to follow this project's Code of Conduct

[lgrammel]

I think this would be useful to have.

[gdaybrice]

Great, let me know if I need to change anything.

[rogercbe]

I think both options and experimental_context would be really useful to have as arguments. The way I see it, options is where I define "global" session variables such as userId, teamId, etc that are passed once... While experimental_context can hold data derived from other tools and steps and can mutate between steps.