[BUG] When Claude Code receives HTTP 404 with a session ID error from an MCP server it should start a new session but it doesn'ty.

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?

Claude Code V2.0.17

Using an MCP server that works fine with GitHub Co-pilot I get error with Claude Code.

MCP server is HTTP only. It works for a bit then I get: Error: Error POSTing to endpoint (HTTP 404): {"error":{"code":-32001,"message":"Session not found"},"id":"","jsonrpc":"2.0"}

Claude Code diagnosis is:
According to the MCP spec: When a server terminates a session, it responds with HTTP 404. When Claude Code receives HTTP 404 with a session ID error, it should start a new session by sending a new InitializeRequest without a session ID, but it's not doing that properly.

Your MCP server is likely returning 404 "Session not found" (correctly per spec), but Claude Code isn't re-initializing the session like it should. Other clients handle this correctly, which is why it works elsewhere.

Solutions

1. Update Claude Code - Check if you're on the latest version
2. File a bug report at https://github.com/anthropics/claude-code/issues with your specific Forrit CMS server details
3. Ask Forrit CMS if they can add stdio transport support as a workaround

This is definitely a Claude Code bug, not your configuration. (Claude's opinion not mine)

What Should Happen?

It should start a new session by sending a new InitializeRequest without a session ID

Error Messages/Logs

Error: Error POSTing to endpoint (HTTP 404): {"error":{"code":-32001,"message":"Session not found"},"id":"","jsonrpc":"2.0"}

Steps to Reproduce

Give the agent a task to do that requires extensive use of the MCP server and at some point it will hit this error and not recover

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.0.17

Platform

Anthropic API

Operating System

Ubuntu/Debian Linux

Terminal/Shell

VS Code integrated terminal

Additional Information

this issue occurs in either the Claude Code running on WSL2 or the integrated VSCode plugin for Claude Code