[BUG] MCP tools not available in VS Code extension due to tool search experiment (tengu_tst_kx7)

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

MCP tools work correctly in the terminal CLI but are not exposed to Claude in the VS Code extension. Debug logs show all three MCP servers connect successfully, but the tools are being hidden by an A/B test experiment.

Environment

• Claude Code VS Code Extension: 2.1.31
• Claude Code CLI: 2.1.29
• OS: Linux (Ubuntu)
• Node: v20.19.0

What Should Happen?

Fix the VS Code extension to properly expose MCP tools regardless of the tool search experiment
Provide a way for users to opt-out of this experiment
Exclude MCP tools from the "deferred tools" behavior

Error Messages/Logs

Steps to Reproduce

MCP Configuration (.mcp.json)

{
  "mcpServers": {
    "support_indexer": {
      "command": "npx",
      "args": ["-y", "@modelcontextprotocol/server-postgres", "postgresql://..."]
    },
    "clickup": {
      "command": "npx", 
      "args": ["-y", "mcp-remote", "https://mcp.clickup.com/mcp"]
    },
    "slack": {
      "command": "npx",
      "args": ["-y", "mcp-remote", "https://mcp.slack.com/sse"]
    }
  }
}

Evidence from Debug Logs
MCP servers connect successfully:

MCP server "slack": Successfully connected to stdio server in 1375ms
MCP server "support_indexer": Successfully connected to stdio server in 1435ms
MCP server "clickup": Successfully connected to stdio server in 2527ms
But tools are hidden by experiment:

Tool search disabled via experiment (tengu_tst_kx7): below threshold, deferred tools present [source: analyzeMcp]
Reproduction
Configure MCP servers in .mcp.json
Open project in VS Code with Claude Code extension
Ask Claude to use an MCP tool (e.g., "query the database")
Claude reports "No such tool available"
CLI workaround confirms servers work:

claude -p "Use mcp__support_indexer__query to run SELECT COUNT() FROM users" --allowedTools 'mcp__'

Works - returns 572 users

claude -p "Use mcp__clickup__clickup_get_workspace_hierarchy" --allowedTools 'mcp__*'

Works - returns workspace structure

claude -p "Use mcp__slack__slack_list_channels" --allowedTools 'mcp__*'

Works - returns 25 channels

Attempted Fix
Tried setting ENABLE_TOOL_SEARCH=false via VS Code settings based on this log line:

[ToolSearch:optimistic] mode=tst-auto, ENABLE_TOOL_SEARCH=undefined, result=true
Added to VS Code settings.json:

"claudeCode.environmentVariables": {
"ENABLE_TOOL_SEARCH": "false"
}
Result: Did not fix the issue. MCP tools still hidden after VS Code restart.

Expected Behavior
MCP tools should be available to Claude in VS Code extension, same as in the CLI.

Impact
This completely breaks MCP functionality in VS Code. Users must either:

Use the terminal CLI instead of VS Code extension
Use clunky workaround: claude -p "..." --allowedTools 'mcp__*' via Bash tool
Request
Please either:

Fix the VS Code extension to properly expose MCP tools regardless of the tool search experiment
Provide a way for users to opt-out of this experiment
Exclude MCP tools from the "deferred tools" behavior

Claude Model

Not sure / Multiple models

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.32

Platform

Anthropic API

Operating System

Ubuntu/Debian Linux

Terminal/Shell

VS Code integrated terminal

Additional Information

_No response_