[BUG] [Desktop] Pinned messages ("chapters") have no visible index/TOC after update

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

After updating Claude Desktop, pinned messages ("chapters") can still be created, but there is no place in the UI to view or navigate them.

Before the update, pinned messages were shown as a table of contents in the side panel and allowed jumping between key points in long sessions.

Now:

• Pinning works: hovering an already-pinned message shows the "Unpin chapter" tooltip.
• No chapter list exists anywhere:
• not in the right-panel menu (Artifacts / Side chat / Background tasks / Plan),
• not in the sidebar session context menu (Open in / Pin / Mark as unread / Rename / Fork / Move to / Archive / Delete),
• not in the session title dropdown.

Previously reported as #57628 (closed as stale), still reproducible.

What Should Happen?

Expected behavior: A chapter index (e.g. a "Chapters" view in the right panel) listing pinned messages, each clickable to scroll to that message — as before the update.

Actual behavior: Chapters can be created but are invisible and cannot be used for navigation.

Error Messages/Logs

Steps to Reproduce

1. Open a long session in the Code tab.
2. Hover a message → click the pin icon ("Pin as chapter").
3. Hover the same message → tooltip now shows "Unpin chapter".
4. Look for a chapter list / TOC anywhere in the UI → none found.

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

Claude Desktop build before 2026-10-15 update

Claude Code Version

2.37337.1

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Other

Additional Information

Reproduced in the Claude Desktop app (Code tab), not in a terminal — Terminal/Shell field is not applicable.
Previously reported as #57628 (closed as stale).
Screenshots attached: "Unpin chapter" tooltip on a pinned message; right-panel menu and session context menu showing no chapter/TOC entry.