[BUG] VS Code "Manage Plugins" shows "No plugins available" after adding second marketplace (e.g. anthropic-agent-skills)

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 adding two marketplaces in the VS Code extension, the "Manage Plugins" panel stops showing available plugins entirely — it shows "No plugins available. Add a marketplace to discover plugins." even though marketplaces are correctly configured.

The CLI is unaffected.

What Should Happen?

Expected behavior

The "Manage Plugins" panel should update correctly after adding a new marketplace and continue showing available plugins.

Error Messages/Logs

SyntaxError: Unterminated string in JSON at position 65496 (line 1490 column 101)

Steps to Reproduce

Environment

Claude Code VS Code extension: 2.1.101
Platform: macOS arm64 (Darwin 25.0.0)
Minimal steps to reproduce

Start with the default claude-plugins-official marketplace (plugins panel shows available plugins correctly)
Add anthropic-agent-skills marketplace via the VS Code extension UI
The plugin panel UI does not update after the second marketplace is added
From this point on, "Manage Plugins" shows "No plugins available. Add a marketplace to discover plugins."
Error logs (~/.../exthost/Anthropic.claude-code/Claude VSCode.log)

Received message from webview: {"type":"request","request":{"type":"list_plugins","includeAvailable":true}}
Error processing client request: SyntaxError: Unexpected end of JSON input
After removing anthropic-agent-skills, the error changes to:

Error processing client request: SyntaxError: Unterminated string in JSON at position 65496 (line 1490 column 101)
Root cause analysis

Position 65496 ≈ 65536 bytes (64 KB) — the list_plugins includeAvailable:true subprocess output is being truncated at the OS pipe buffer limit.

claude-plugins-official alone: ~59 KB → works fine
claude-plugins-official + anthropic-agent-skills: the anthropic-agent-skills marketplace directory is 14 MB with 17 skill subdirectories. The plugin lister appears to scan these skill files and include their content in the response, pushing the total well past 64 KB → truncated JSON → parse failure

Suggested fix

Use a temp file or streaming output instead of a single stdout write for list_plugins includeAvailable:true, to avoid the OS pipe buffer limit with large marketplace datasets.

Claude Model

None

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.104

Platform

Other

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_