[BUG] VS Code extension: no "show more/less" collapse for expanded custom slash command content

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?

When invoking a custom slash command (e.g. /gstack-review) in the Claude Code VS Code extension, the full expanded content of the command file is displayed in the chat transcript as plain, non-collapsible text — even when it is very long (100+ lines). By contrast, a regular typed user message of similar or even shorter length gets a "Show more / Show less" collapse toggle.

This makes the chat panel very cluttered and hard to scroll through when using custom slash commands with long definitions.

What Should Happen?

Expanded custom slash command content should be wrapped in the same collapsible "Show more / Show less" component used for long typed messages, so long command definitions don't dominate the scroll view.

Steps to Reproduce

Create a custom command file with 100+ lines in .claude/commands/ (e.g. gstack-review.md)
Open the Claude Code VS Code extension chat panel
Type /gstack-review and send it
Observe the full file content is rendered in the transcript with no collapse/expand control, unlike a normal long typed message

Expected Behavior
The command block should be collapsible like standard long messages.

Actual Behavior
The command block renders in full with no truncation or "show more/less" toggle.

Environment

Claude Code extension version: [check via Extensions panel → Claude Code → version number]
VS Code version: [Help → About]
OS: [Windows/macOS/Linux + version]
Claude model: [e.g. Sonnet 5]

Error Messages/Logs

Steps to Reproduce

In a project folder, create the directory .claude/commands/ if it doesn't exist.
Create a file .claude/commands/long-test.md with long content, for example:
markdown

Long test command

This is a test command with many lines to reproduce a UI issue.

Line 1 of filler content for testing purposes.
Line 2 of filler content for testing purposes.
Line 3 of filler content for testing purposes.
[... repeat similar lines up to ~150 lines total ...]
Line 150 of filler content for testing purposes.

Final instruction: acknowledge this command was received.

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.138

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Other

Additional Information

_No response_