feat: agent / vector_store as tool

[0xMochan]

• I have looked for existing issues (including closed) about this

Feature Request

Be able to attach an agent as a tool. This would allow agent-directed flow since the agent itself can choose what agents to refer to.

Motivation

• Studying the OpenAI Agent SDK led to this idea.

Proposal

• Implement Tool for Agent (and maybe VectorStore)

Alternatives

• Wrapper Tool

[linear]

RIG-727 feat: agent as tool