Tool Search doesn't activate automatically despite tengu_mcp_tool_search flag - requires ENABLE_TOOL_SEARCH env var

Description

Tool Search for MCPs doesn't activate automatically even when:

• MCP tools consume >35% of context (~70k tokens)
• The tengu_mcp_tool_search: true flag is present in ~/.claude.json

The feature only works when explicitly setting ENABLE_TOOL_SEARCH=true environment variable.

Environment

• Claude Code version: 2.1.7
• Model: claude-opus-4-5-20251101
• Platform: macOS Darwin 25.2.0
• MCPs configured: 8 servers (gmail, google-calendar, google-drive, notion, notion-joy, context7, playwright, claude-in-chrome)

Steps to Reproduce

1. Configure multiple MCP servers in ~/.claude.json (total ~70k tokens)
2. Start Claude Code normally: claude
3. Run /context to check token usage
4. Observe: MCP tools show ~70k tokens (35%+ of context), NOT "loaded on-demand"

Expected Behavior

According to the official announcement, Tool Search should activate automatically when MCP tool descriptions exceed 10% of context:

"Claude Code detects when your MCP tool descriptions would use more than 10% of context. When triggered, tools are loaded via search instead of preloaded."

Actual Behavior

• MCP tools are fully loaded into context (~70k tokens)
• Tool Search doesn't activate despite being well above the 10% threshold
• The tengu_mcp_tool_search: true flag in config has no effect

Workaround

Explicitly set the environment variable:

ENABLE_TOOL_SEARCH=true claude

Or add to ~/.zshrc:

export ENABLE_TOOL_SEARCH=true

Results After Workaround

| Metric | Without env var | With ENABLE_TOOL_SEARCH=true |
|--------|-----------------|------------------------------|
| MCP tools | 70.5k tokens (35.3%) | 0 tokens (on-demand) |
| Total initial | 98k tokens (49%) | 23k tokens (11%) |
| Free space | 57k tokens | 132k tokens |

Questions

1. Is ENABLE_TOOL_SEARCH=true supposed to be required, or should it activate automatically based on the 10% threshold?
2. What is the purpose of tengu_mcp_tool_search flag if it doesn't enable the feature?
3. Should this be documented more prominently?

Thank you!