feat(sdk): add tool call extension

[pilartomas]

Signed-off-by: Tomas Pilar [email protected]

Summary

This PR adds a new MCP Tool Call Extension to AgentStack SDK.

This new extension should not be confused with existing MCP Service Extension. The purpose of the latter is to allow A2A clients provide MCP servers dynamically. The new extension is more akin to the oAuth extension, providing additional support to arbitrary MCP clients.

Linked Issues

Closes #1560

Documentation

• No Docs Needed:

If this PR adds new feature or changes existing. Make sure documentation is adjusted accordingly. If the docs is not needed, please explain why.

[matoushavlena]

I think calling this an MCP extension is confusing. We should consider different naming (eliciation, tool approval, etc.).

[pilartomas]

The idea was that it will cover more than just tool approvals but I was thinking of some "capabilities" to turn on and off, we should have a discussion also with @tomkis on the right approach.

[pilartomas]

Eventually, we may allow argument modification etc.

[pilartomas]

Supports Claude-like user experience:

Agent would like to call tool X of server Y with arguments A, do you approve?

Implementation of always allow is left upon the client.

[tomkis]

I started with the review by reading the docs - without any prior context.

My biggest concern currently is that i had to zoom in to the code to understand how it actually works; It's just a semantic layer on top of Input required that maps MCP tool metadata.

What i originally anticipated was an extension that would somehow automagically plug into the MCP client to handle the tool approval for me, which is not the case.

This is not necessarily a bad, however it is confusing because i think most users will be searching how to solve "real problem" - how do i let agenstack ui approve my MCP tools.

Couple suggestions:

1. Preface the docs with explanation that this does not solve the actual approval, but only provides a message protocol how to request the approval
2. Add real world example in beeai framework how you can actually intercept the tool calling
3. I'd completly refrain from using single word MCP and depending on MCP interfaces -> create custom layer (that can mimic the MCP) so that people don't get confused that this is some MCP magic.

[pilartomas]

@tomkis Changed, please have another look 👍