[FEATURE] Pin/persist a single response for reference during follow-ups

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

Long responses scroll out of view quickly. When asking follow-up questions, I lose easy access to a key earlier answer. I currently work around this by copy-pasting output into Mac Notes — clunky and breaks flow.

Proposed Solution

A way to "pin" one or more individual assistant responses so they stay accessible while the conversation continues. Ideal behaviors:

• Pin a specific message (keystroke or /pin), unpin to release.
• Pinned content viewable on demand (e.g. a side panel, a /pinned view, or a sticky region) without re-scrolling.
• Optionally export pinned items to a file.

Alternative Solutions

Alternatives considered, all insufficient:

• Scrollback / --resume / /export — scrollback gets hidden mid-session (#41907); --resume reloads the whole session; /export dumps the entire conversation — none surface one chosen answer.
• Copy-paste into an external notes app (current workaround) — clunky, breaks flow, lives outside the tool.

Priority

Medium - Would be very helpful

Feature Category

Interactive mode (TUI)

Use Case Example

I ask Claude Code to explain a deployment process, and it returns a detailed 40-line answer with commands and caveats. I then ask several follow-up questions ("what about rollback?", "which flag for staging?"). Each new response pushes the original 40-line answer out of view, and mid-session redraws hide it entirely (#41907). To keep referring back to it, I copy-paste that answer into Mac Notes and alt-tab between windows.

With a pin: I'd press a key (or run /pin) on that one response to keep it accessible — in a side panel or via /pinned — and continue the conversation without losing it or leaving the terminal. When done, I'd unpin it.

Additional Context

• Related Claude Code issues:
• #13591 (sticky/fixed input)
• #41907 (previous output hidden during session)
• #42670/#41814 (conversation history not accessible)
• This request is distinct: pinning a specific chosen response, not fixing scrollback or sticky input.
• Frequency: Hits on most multi-step sessions (debugging, deployments, long explanations) where I reference an earlier answer repeatedly.