[BUG] "Pin as chapter" / mark_chapter has no visible UI (chapter index/TOC missing)

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?

Description

The "Pin as chapter" context menu option and the mcp__ccd_session__mark_chapter
tool appear to work (no error), but no chapter index, divider, or table of contents
shows up anywhere in the UI after pinning.

Environment

• OS: Windows 11 Pro 10.0.26200
• Claude Code: [versión — Help → About]
• Model: Opus 4.7

Steps to reproduce

1. Right-click any message → "Pin as chapter" → enter title
2. Look for a chapter index, sidebar, or divider in the transcript
3. Nothing appears

Expected

A floating table of contents / divider / sidebar listing pinned chapters,
allowing navigation between them.

Actual

No visible indicator that the chapter was pinned. No panel toggle found
in View menu or sidebar.

What Should Happen?

After pinning a message with "Pin as chapter", the chapter should appear
somewhere visible in the UI — either as a divider in the transcript at
the pinned location, or as an entry in a chapters/outline sidebar or
floating table of contents that lets me jump between pinned chapters.

Currently nothing visible happens after pinning, so I cannot navigate
between chapters or confirm the pin was registered.

Error Messages/Logs

No error messages. The "Pin as chapter" action completes silently — 
no error dialog, no console error, no toast notification, and no visible 
UI change. The tool appears to succeed but produces no observable output.

Steps to Reproduce

1. Open Claude Code Desktop on Windows 11
2. Start any conversation (or open an existing session)
3. Right-click on any message in the transcript
4. From the context menu, select "Pin as chapter"
5. Enter a chapter title in the dialog and confirm
6. Observe the transcript and surrounding UI

Expected: a chapter divider appears in the transcript at the pinned
location, or a chapters panel/index becomes visible.

Actual: nothing visible changes. The dialog closes, no divider appears,
no sidebar or table of contents shows up, no toast notification confirms
the pin. There is no way to tell whether the pin was registered or
where to navigate to it.

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.87

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Windows Terminal

Additional Information

_No response_