simulate: attribute tool calls and handoffs to the agent in TUI transcript

[u9g]

Tool calls, tool outputs, and handoffs follow the triggering user message in the chat history, so the TUI transcript rendered them under the You header. Open an Agent block for them instead; the agent's spoken reply merges into that block.

Before:

Agent
  gotcha, Monday at 10 it is. lemme just get that locked in for you.
  ƒ schedule_appointment()
  ⤳ front_desk_agent → get_email_task

Agent
  Could you please provide your email address?

You
  Do you really need that? It's a@b.com.
  ƒ update_email_address({"email":"a@b.com"})
  ⤳ get_email_task → front_desk_agent

Agent
  oh, yeah, sorry about that! you're all set for Monday at 10.

After:

Agent
  gotcha, Monday at 10 it is. lemme just get that locked in for you.
  ƒ schedule_appointment()
  ⤳ front_desk_agent → get_email_task

Agent
  Could you please provide your email address?

You
  Do you really need that? It's a@b.com.

Agent
  ƒ update_email_address({"email":"a@b.com"})
  ⤳ get_email_task → front_desk_agent
  oh, yeah, sorry about that! you're all set for Monday at 10.