[BUG]

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?

MCP tools are consistently unavailable on the very first user prompt of a new Claude Code session, but work correctly on all subsequent prompts.

• claude mcp list shows servers "✓ Connected"
• First MCP tool call fails: Error: No such tool available: mcp__<server>__<tool>
• Any follow-up message, then retry same tool → works perfectly

This appears to be a race condition where the MCP tool registry isn't fully populated until after the first response cycle completes.

What Should Happen?

MCP tools should be available immediately when session starts, since claude mcp list confirms they're connected.

Error Messages/Logs

Error: No such tool available: mcp__ucis-kafka-mcp__get_recent_memories_temporal

Steps to Reproduce

Error: No such tool available: mcp__ucis-kafka-mcp__get_recent_memories_temporal
Steps to Reproduce:

1. Configure multiple MCP servers via claude mcp add
2. Verify connection: claude mcp list shows "✓ Connected" for all
3. Start fresh Claude Code session
4. First message: request that requires MCP tool
5. Observe: "No such tool available" error
6. Send any follow-up message
7. Retry exact same MCP tool call
8. Observe: Tool now works correctly

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.0.75

Platform

Anthropic API

Operating System

Ubuntu/Debian Linux

Terminal/Shell

Terminal.app (macOS)

Additional Information

Related issues that may be duplicates or related:

• #12164 - MCP servers connect but tools not exposed
• #2682 - MCP Tools Not Available in Conversation Interface
• #11175 - Tools visible but unavailable to assistant
• #14496 - Subagents fail to access MCP tools

Environment: 10+ custom Python MCP servers via stdio transport, Ubuntu Linux.

The pattern suggests MCP tool registration happens asynchronously and isn't complete before Claude begins processing the first user prompt.