[BUG] VSCode extension on WSL doesn't show MCP-provided slash commands (works in CLI)

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?

The Claude Code VSCode extension (latest, running against a WSL2 Ubuntu 24.04 workspace via Remote-WSL) does not show slash commands provided by an MCP server's prompts capability. The MCP server itself connects successfully and its tools are usable — only the prompts are missing from the / slash-command picker. Running claude in a WSL terminal opened in the exact same project directory shows all 21 prompts correctly, so the issue is specific to the extension's surface, not the MCP server or its registration.

Tested with iflow-mcp (a custom MCP server, Bun-compiled single binary) registered project-scope via .mcp.json. Exposes 21 prompts and 38 tools.

Environment:

Claude Code CLI: 2.1.143
VSCode: 1.120.0
Claude Code VSCode extension: 2.1.143
WSL2, Ubuntu 24.04.1 LTS, kernel 5.15.167.4-microsoft-standard-WSL2

What Should Happen?

All MCP-provided prompts should appear in the slash-command picker inside the VSCode extension, identical to the CLI behavior. Registering an MCP server via .mcp.json should surface both its tools and its prompts in any Claude Code client — CLI and extension alike.

Error Messages/Logs

Steps to Reproduce

1. On Windows host with WSL2 + Ubuntu 24.04, install Claude Code VSCode extension (latest) and Claude Code CLI 2.1.143 inside WSL.
2. In a project directory inside WSL, create .mcp.json registering an MCP server that exposes prompts (e.g. iflow-mcp):

{
"mcpServers": {
"iflow": {
"type": "stdio",
"command": "/absolute/path/to/iflow-mcp"
}
}
}

1. Open the project in VSCode via "WSL: Open Folder in WSL".
2. Launch Claude Code through the VSCode extension panel.
3. Type / in the input box — note that none of the MCP-provided prompts appear (only built-in skills/commands).
4. Open a WSL terminal in the same directory, run claude, type / — observe that all MCP-provided prompts appear correctly.

Workaround: use Claude Code CLI in WSL terminal instead of the VSCode extension.

Claude Model

Sonnet (default)

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.143

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

WSL (Windows Subsystem for Linux)

Additional Information

_No response_