Feature Request: Support switch interactions when busy

[liaowang11]

Checklist

• I agree to communicate with the author myself (not AI-generated).
• I've read the README's Filing issues section.
• I'm running the latest versions (fill in below).
  • agent-shell version: v0.45.1
  • acp.el version: 0.11.3
  • ACP package (e.g. claude-agent-acp) version: latest
  • Agent CLI (e.g. claude, gemini) version: latest
• For requesting new agent support, I'm including a link to the ACP-capable agent or related ACP package.
• For issues, I'm including ACP traffic (as per README).

New Feature

When a user switches the viewport to view previous interactions while a response is actively streaming, we should support navigating the history without interrupting the stream.

Rational

• We can review previous interaction for next action while the agent is busy working.
• Currently there is a bug that allows this: just return to agent-shell-mode then C-c C-o on previous interaction to view that interaction. (And it actually streaming to that page)

[rudolf-adamkovic]

This would be 🥇 to have.